| 1. |
- Ghasemi, Rohollah, 1983-, et al.
(författare)
-
Abrasion resistance of lamellar graphite iron : Interaction between microstructure and abrasive particles
- 2018
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 120, s. 465-475
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on abrasion resistance of Lamellar Graphite Iron (LGI) using microscratch test under constant and progressive load conditions. The interactions between a semi-spherical abrasive particle, cast iron matrix and graphite lamellas were physically simulated using a sphero-conical indenter. The produced scratches were analysed using LOM and SEM to scrutinise the effect of normal load on resulting scratch depth, width, frictional force, friction coefficient and deformation mechanism of matrix during scratching. Results showed a significant matrix deformation, and change both in frictional force and friction coefficient by increase of scratch load. Furthermore, it was shown how abrasive particles might produce deep scratches with severe matrix deformation which could result in graphite lamella's coverage and thereby deteriorate LGI's abrasion resistance.
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| 2. |
- Akhavan Attar, Ali, et al.
(författare)
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High Strength-Elongation Balance in Warm Accumulative Roll Bonded AA1050 Sheets
- 2022
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Ingår i: Metals and Materials International. - : Springer. - 1598-9623 .- 2005-4149. ; 28, s. 346-360
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Tidskriftsartikel (refereegranskat)abstract
- Several studies had been performed on accumulative roll bonding (ARB) for AA1050; however, most of them were conducted at room temperature. Here, the ARB process was performed on AA1050 plates through nine cycles at elevated temperature. An innovation introduced a new parameter (UTS×El.ε) to compare the strength-elongation balance between the present study and previous works. Also, as another parameter, the toughness was compared. Comparing these parameters with previous works showed that the considered samples in the present study performed 14 to 63% better than the other samples, so they were more industrially favorable in terms of mechanical behavior and performance. ARB process at elevated temperature may slightly lead to grain growth compared to room/cryogenic temperature, but creates a better elongation, which ultimately leads to a better balance of the strength-elongation parameter. The results showed that the effect of inter-cycle heating was found significant on microstructural evolution and mechanical behavior. Upon five cycles of the process, the grain size was decreased from 35 to 1.8 μm. The yield strength and ultimate strength increased up to 305% and 94%, respectively. Microhardness test showed that warm ARB reduces inhomogeneity factor in the thickness after 3 cycles. Fractography by SEM showed that the sample failed through shear ductile rupture and that the dimples became smaller, more elongated, and shallower onto the failure surface as the number of ARB cycles increased. In short, the warm process is preferred to the cold process to achieve better mechanical performance and toughness.
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| 3. |
- Akhavan Attar, Ali, et al.
(författare)
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Improving the fracture toughness of multi-layered commercial pure aluminum via warm accumulative roll bonding
- 2021
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 116, s. 3603-3617
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the fracture toughness of the multi-layered commercial pure aluminum samples (AA1050) prepared by warm accumulative roll bonding (WARB) was investigated for the first time. Based on the ASTM E561 standard, the R-curve method was utilized to measure the plane stress fracture toughness. Compact tension (CT) samples were prepared from the sheets that were processed by different ARB cycles. Mechanical properties, microstructure, and fracture surfaces of the CT samples were studied by uniaxial tensile test, electron backscatter diffraction (EBSD), and scanning electron microscopy (SEM), respectively. By increasing the number of WARB cycles, fracture toughness increased; after five cycles, 78% enhancement was observed compared to the pre-processed state. A correlation was seen between the fracture toughness variations and ultimate tensile strength (UTS). WARB enhanced UTS up to 95%, while the grain size showed a reduction from 35 to 1.8 μm. Measured fracture toughness values were compared with the room temperature ARB outcomes, and the effective parameters were analyzed. Fractography results indicated that the presence of tiny cliffs and furrows and hollow under fatigue loading zones and shear ductile rupture in the Quasi-static tensile loading zone.
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| 4. |
- Ashrafi, Hamid, et al.
(författare)
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Damage Micromechanisms in Friction Stir-Welded DP600 Steel during Uniaxial Tensile Deformation
- 2022
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Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 31, s. 10044-10053
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Tidskriftsartikel (refereegranskat)abstract
- In this study, damage initiation micromechanisms in friction stir-welded DP600 steel sheets during tensile deformation were studied by scanning electron microscopy (SEM) and electron backscatter diffraction. For this purpose, DP600 steel was welded using friction stir welding with two combinations of rotational and transverse speed, to prepare joints with low and high heats. Microhardness measurements on the cross section of the weldments revealed the formation of a softened zone in the HAZ as a result of the tempering of the martensite, which led to the localization of strain and failure during the tensile testing. SEM observations on the cross section of tensile tested specimens showed that ferrite–martensite interface decohesion and martensite fracture are the main void nucleation mechanisms in the DP600 steel. For the sample welded with low heat input, ferrite–martensite interface decohesion started at higher strains compared to the DP600 steel. A new void initiation mechanism including plastic deformation of tempered martensite, necking, separation of martensite fragments and formation of a void between the separated segments was also suggested for this sample. For the sample welded with high heat input, formation of void at the ferrite–cementite interface was the main void nucleation mechanism and ferrite–martensite interface decohesion was an inactive mechanism.
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| 5. |
- Ashrafi, Hamid, et al.
(författare)
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Void formation and plastic deformation mechanism of a cold-rolled dual-phase steel during tension
- 2020
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer. - 1006-7191 .- 2194-1289. ; 33, s. 299-306
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Tidskriftsartikel (refereegranskat)abstract
- The void formation and plastic deformation micromechanisms of a cold-rolled DP600 steel during tensile loading were studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The SEM observations revealed that the main void nucleation mechanism in the DP600 steel is decohesion at the ferrite–martensite interfaces. The voids were mostly observed between the closely spaced martensite islands situated at the boundaries of relatively finer ferrite grains. The EBSD results indicated a strain gradient developed from the ferrite–martensite and ferrite–ferrite interfaces into the interior of ferrite grains during the tensile deformation, which led to a stress concentration at these interfaces. Moreover, it was demonstrated that local misorientation inside the finer ferrite grains surrounded by martensite islands was higher than that for the coarser ferrite grains, which made the former more prone to void initiation.
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| 6. |
- Bjurenstedt, Anton, 1979-, et al.
(författare)
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The effect of Fe-rich intermetallics on crack initiation in cast aluminium : an in-situ tensile study
- 2019
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 756, s. 502-507
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Tidskriftsartikel (refereegranskat)abstract
- To evaluate the role of Fe-rich intermetallics on crack initiation, two fully modified Al-Si alloys, one containing plate-like β-Fe and the second containing primary α-Fe intermetallics, were investigated by in-situ tensile testing in the scanning electron microscope. In the first alloy, large plate-like β-Fe intermetallics oriented parallel to the test direction were the first to crack at an elongation of about 1.8%. More transversely oriented intermetallics caused crack initiation in the matrix which linked up with the final fracture. In the second alloy, the cracking of α-Fe intermetallics initiated at an elongation of about 0.9%. It is concluded that large α-Fe intermetallics crack first and that clusters of α-Fe are the most potent crack initiation sites.
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| 7. |
- Bogdanoff, Toni, et al.
(författare)
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A simple procedure to assess the Complete Melt Quality in aluminium castings : implementation in a die-casting and a rheo-casting
- 2024
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Ingår i: International Journal of Cast Metals Research. - : Taylor & Francis. - 1364-0461 .- 1743-1336. ; 37:1, s. 71-79
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Tidskriftsartikel (refereegranskat)abstract
- A new simple approach was developed to assess the Complete Melt Quality of aluminium cast alloys throughout the production line. The approach relies on the concurrent use of reduced pressure tests (RPT) and tensile tests at each station in the production line when the melt is transferred and/or processed. These tests can be used to determine the source of melt-related problems in the production line. Two case studies from the procedure of both an aluminium die-casting and a rheo-casting plant showed that melts were significantly damaged in the tower furnace and got progressively more damaged through the production line proven by the RPT, tensile test, and fracture surface analysis results.
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| 8. |
- Bogdanoff, Toni, et al.
(författare)
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On the combined effects of surface quality and pore size on the fatigue life of Al–7Si–3Cu–Mg alloy castings
- 2023
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 885
-
Tidskriftsartikel (refereegranskat)abstract
- This study has aimed to determine the effects of surface quality and pore size, obtained by different levels of hydrogen content of the liquid metal, on the fatigue behavior of an Al–7%Si–3%Cu–Mg casting alloy. Three surface conditions have been studied: as-cast rough, as-cast smooth, and standard machined and polished surface. The S–N curves have shown that surface roughness and hydrogen content individually impact fatigue strength. Surprisingly, the fatigue strength of machined and polished samples, which aligns with standard testing practices, is significantly reduced, compared to other conditions. Fatigue cracks have been observed to initiate at the pores just below the as-cast surface or on the machined surfaces. In all cases, pores have been observed to be surrounded by bifilms. Moreover, hydrogen content and roughness of the as-cast surface have been found to interact to determine the fatigue performance. These findings necessitate a re-evaluation of fatigue testing procedures for cast aluminum components.
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| 9. |
- Bogdanoff, Toni, et al.
(författare)
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On the Effectiveness of Rotary Degassing of Recycled Al-Si Alloy Melts : The Effect on Melt Quality and Energy Consumption for Melt Preparation
- 2023
-
Ingår i: Sustainability. - : MDPI. - 2071-1050. ; 15:6
-
Tidskriftsartikel (refereegranskat)abstract
- The effectiveness of rotary degassing on the defect formation and mechanical properties of the final casting of aluminium alloy EN AC 46000 was investigated, along with its impact on the energy consumption in the casting furnace. In the melt preparation prior to casting, the molten metal is usually transported from the melting furnace to the casting furnace with rotary degassing as a cleaning procedure. Under the conditions of this specific study, negligible degradation was observed in the mechanical properties of the final cast component in an aluminium EN AC 46000 alloy after removing the rotary degassing step in the process. Furthermore, removing the rotary degassing step led to a reduced temperature drop in the melt, thus minimizing the need for reheating (energy consumption) by up to 75% in the casting furnace. The reduced energy consumption was up to 124,000 kWh in yearly production in a 1500 kg casting furnace. The environmental impact showed a similar to 1500 kg reduction in CO2 for one 1500 kg electrical casting furnace in a year.
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| 10. |
- Bogdanoff, Toni, et al.
(författare)
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On the secondary cracks during crack propagation in an Al-Si-Cu-Mg alloy : An in-situ study
- 2023
-
Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 203
-
Tidskriftsartikel (refereegranskat)abstract
- During in situ cyclic testing of hot isostatically pressed and heat-treated Al-5Si-0.5 Mg-1Cu alloy castings, cracks were observed to open up in places far away from the area of stress concentration. Cyclic testing was interrupted to assess these cracks. Analysis showed that these cracks originated from oxide bifilms that were entrained in the liquid state. Moreover, Si and Fe-rich intermetallics were observed to have precipitated on these bifilms. These finding makes it necessary to re-evaluate how damage is interpreted in mechanical studies. Entrainment damage, which takes place in the liquid state, may remain invisible in non-destructive inspection and can significantly affect fatigue properties when bifilms open up under low tensile stresses and present the propagating crack a path of low resistance during propagation.
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| 11. |
- Bogdanoff, Toni, et al.
(författare)
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Prototyping of a high pressure die cast al-si alloy using plaster mold casting to replicate corresponding mechanical properties
- 2019
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Ingår i: Minerals, Metals and Materials Series. - Cham : Springer. - 9783030058630 - 9783030058647 ; , s. 435-442
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Konferensbidrag (refereegranskat)abstract
- Prototyping prior high pressure die casting (HPDC) is used for product/mold design optimization. Plaster mold casting is a cost-efficient prototyping technique providing good surface quality and dimension accuracy, similar to HPDC components. However, the corresponding mechanical properties of a component produced with these two methods are diverging significantly, mainly due to differences in the cooling rate. This work presents a procedure to optimize the plaster mold casting for prototyping to replicate mechanical properties of a commonly used Al-Si alloy (A380). Two commercial alloys with compositions close to the A380 alloy (A356.0 and A360.2) were used. Yield strength was considered as the main design criteria, thus the target mechanical property. Tensile testing results showed that with an optimized T6 heat treatment, not only the yield strength, but also ultimate tensile strength and elongation correspond well to the properties in the HPDC component.
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| 12. |
- Bogdanoff, Toni, et al.
(författare)
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The complex interaction between microstructural features and crack evolution during cyclic testing in heat-treated Al–Si–Mg–Cu cast alloys
- 2021
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 825
-
Tidskriftsartikel (refereegranskat)abstract
- The study aimed to investigate crack initiation and propagation at the micro-scale in heat-treated Al–7Si–Mg cast alloys with different copper (Cu) contents. In-situ cyclic testing in a scanning electron microscope coupled with electron back-scattered diffraction and digital image correlation was used to evaluate the complex interaction between the crack path and the microstructural features. The three-nearest-neighbour distance of secondary particles was a new tool to describe the crack propagation in the alloys. The amount of Cu retained in the α-Al matrix after heat treatment increased with the Cu content in the alloy and enhanced the strength with a slight decrease in elongation. During cyclic testing, the two-dimensional (2D) crack path appeared with a mixed propagation, both trans- and inter-granular, regardless of the Cu content of the alloy. On fracture surfaces, multiple crack initiation points were detected along the thickness of the samples. The debonding of silicon (Si) particles took place during crack propagation in the Cu-free alloy, while cracking of Si particles and intermetallic phases occurred in the alloy with 3.2 wt% Cu. Three-dimensional tomography using focused ion beam revealed that the improved strength of the α-Al matrix changes the number of cracked particles ahead of the propagating crack with Cu concentration above 1.5 wt%.
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| 13. |
- Bogdanoff, Toni
(författare)
-
The effect of microstructural features, defects and surface quality on the fatigue performance in Al-Si-Mg Cast alloys
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global warming is driving industry to manufacture lighter components to reduce carbon dioxide (CO2) emissions. Promising candidates for achieving this are aluminium-silicon (Al-Si) cast alloys, which offer a high weight-to-strength ratio, excellent corrosion resistance, and good castability. However, understanding variations in the mechanical properties of these alloys is crucial to producing high-performance parts for critical applications. Defects and oxides are the primary reasons cast components in fatigue applications are rejected, as they negatively impact mechanical properties.A comprehensive understanding of the correlation between fatigue performance and parameters such as the α-aluminium matrix, Al-Si eutectic, surface roughness, porosities, hydrogen content, oxides, and intermetallic phases in Al-Si castings has not been reached.The research presented in this thesis used state-of-the-art experimental techniques to investigate the mechanical properties and crack-initiation and propagation behaviour of Al-Si-Mg cast alloy under cyclic loading. In-situ cyclic testing was conducted using scanning electron microscopy (SEM) combined with electron back-scattered diffraction (EBSD), digital image correlation (DIC), and focused ion beam (FIB) milling. These techniques enabled a comprehensive study of parameters affecting fatigue performance, including hydrogen content, surface roughness, oxides, and intermetallic phases. More specifically, we investigated the effect of melt quality, copper (Cu) content, oxide bifilms, surface quality, and porosity.The increased Cu concentration in heat-treated Al-Si alloys increased the amount of intermetallic phases, which affected the cracking behaviour. Furthermore, oxide bifilms were detected at crack-initiation sites, even in regions far away from the highly strained areas. Si- and Iron (Fe)-rich intermetallics were observed to have precipitated on these bifilms. Due to their very small size, these oxides are generally not detected by non-destructive inspections, but affect mechanical properties because they appear to open at relatively low tensile stresses. Finally, Al-Si alloy casting skins showed an interesting effect in terms of improving fatigue performance, highlighting the negative effect of surface polishing for such alloys.
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| 14. |
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| 15. |
- Bogdanoff, Toni, et al.
(författare)
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The impact of HIP process and heat treatment on the mechanical behavior of an Al-Si-Mg alloy component
- 2023
-
Konferensbidrag (refereegranskat)abstract
- Castings generally contain pores and defects that can have a detrimental impact on mechanical properties. The hot isostatic pressing (HIP) process is usually applied to reduce internal porosities, which improves the mechanical properties because of the closed porosities. Therefore, this study investigates the effect of the HIP process on the mechanical properties of sand casting A356 aluminum alloys. This investigation was performed in collaboration with Unnaryd Modell, Quintus Technologies, and IAC Ankarsrum. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIP process was examined using computed tomography scanning, in-situ cyclic testing, and scanning electron microscope. In the absence of large defects, the fatigue performance was improved. However, a significant variation in the result was found between the different conditions, whereas the coarser microstructure with larger porosities before the HIP process showed decreased ultimate tensile strength and elongation to failure. The samples tested under high cycle fatigue showed a reduced fatigue propagation zone in that the coarser microstructure. Moreover, large cleavage areas containing oxides in the fracture surfaces indicated that the HIP process closes all the porosities, but the oxide films are not creating a strong bonding. Furthermore, the samples tested under low cycle fatigue showed a difference in the crack propagation, whereas the coarser microstructure showed large cracks opened up away from the notch that assists the propagation leading to reduced fatigue life.
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| 16. |
- Bogdanoff, Toni, et al.
(författare)
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The impact of HIP process and heat treatment on the mechanical behaviour of an Al–Si–Mg alloy component
- 2024
-
Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates the effect of hot isostatic pressing (HIPping) on the static and fatigue properties of sand-casting A356 aluminium alloys. HIPping is a method to improve the fatigue properties in aluminium cast material by reducing or eliminating the inner porosities. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIPping process was examined using computed tomography and scanning electron microscopy (SEM). Castings generally contain pores and defects that have a detrimental impact on the fatigue properties. The HIPping process closes the porosities in all investigated samples with an increase in density. Without significant defects, the mechanical performance improved in the finer microstructure. However, a considerable variation in the results was found between the different conditions, whereas the coarser microstructure with larger porosities before HIPping showed remarkably reduced results. The high-cycle fatigue-tested samples showed reduced fatigue propagation zone in the coarser microstructure. Moreover, large cleavage areas containing bifilms in the fracture surfaces indicate that the healing process of porosities is inefficient. These porosities are closed but not healed, resulting in a detrimental effect on the static and dynamic properties.
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| 17. |
- Bogdanoff, Toni, et al.
(författare)
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The influence of copper addition on crack initiation and propagation in an Al–Si–Mg alloy during cyclic testing
- 2020
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Ingår i: Materialia. - : Elsevier. - 2589-1529. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of copper (Cu) addition up to 3.2 wt% on crack initiation and propagation in an Al–Si–Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A combination of digital image correlation, electron backscatter diffraction, and scanning electron microscopy was used to investigate crack initiation and propagation behaviour during in-situ cyclic testing. The results showed that Cu-rich intermetallic compounds with the addition of Cu up to 1.5 wt% do not affect the fatigue behaviour of these alloys, and that crack propagation in these cases is trans-granular and trans-dendritic. However, increasing the concentration of the Cu retained in the primary α-Al matrix in solid solution and Cu-containing precipitates delayed crack propagation during cyclic testing. The results showed that strain accumulation was highest at the grain boundaries; however, the crack preferred to propagate along or across primary α-Al dendrites due to the relatively lower mechanical strength of the matrix compared to the eutectic and intermetallic phases. Moreover, the addition of Cu of more than 3.0 wt% to Al-Si-Mg alloys changes the fatigue behaviour that a rapid failure occurs.
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| 18. |
- Bogdanoff, Toni
(författare)
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The influence of microstructure on the crack initiation and propagation in Al-Si casting alloys
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For reducing the CO2 footprint in many industrial fields, the goal is to produce lighter components. The aluminium-silicon (Al-Si) cast alloys are promising candidates to fulfill these goals with a high weight-to-strength ratio, good corrosion properties, excellent castability, and recyclable material. However, the variations within these components need to be understood to produce high-performance components for critical applications. The main reason for the rejection in these applications is defects and microstructural features that reduce the mechanical properties. The addition of copper (Cu) is one way of increasing the mechanical properties in Al-Si alloys and is commonly used in the automotive industry. Casting defects harm the mechanical properties, and these defects can be reduced by improving the melt quality, the correct design of the component, and the gating system.The study aims to investigate the static mechanical properties and the crack initiation and propagation under cyclic loading in an Al-7Si-Mg cast alloy with state-of-the-art experiments. The main focuses were on the effect of the HIP process and the role of Cu addition. In-situ cyclic testing using a scanning electron microscope coupled with electron back-scattered diffraction, digital image correlation, focused ion beam (FIB) slicing, and computed tomography scanning was used to evaluate the complex interaction between the crack path and the microstructural features.The amount of Cu retained in the α-Al matrix in as-cast and heat-treated conditions significantly influenced the static mechanical properties by increasing yield strength and ultimate tensile strength with a decrease in elongation. The three-nearest-neighbor distance of eutectic Si and Cu-rich particles and crack tortuosity were new tools to describe the crack propagation in the alloys, showing that a reduced distance between the Cu-rich phases is detrimental for the mechanical properties. Three dimensional tomography using a FIB revealed that the alloy with 3.2 wt.% Cu had a significantly increased quantity of cracked Si particles and intermetallic phases ahead of the crack tip than the Cu-free alloy. The effect of Cu and HIP process in this work shows the complex interaction between the microstructural features and the mechanical properties, and this needs to be considered to produce high-performance components.
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| 19. |
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| 20. |
- Conway, Patrick L. J., et al.
(författare)
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High entropy alloys towards industrial applications : High-throughput screening and experimental investigation
- 2022
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 830
-
Tidskriftsartikel (refereegranskat)abstract
- Using the Thermo-Calc implementation of the CALPHAD approach, high-throughput screening of the Co–Cr–Fe–Mn–Ni system was implemented to find ‘islands’ of single phase FCC structure within the compositional space in order to reduce the cost of this well-studied alloy system. The screening identified a region centred around Co10Cr12Fe43Mn18Ni17, reducing the material cost compared to the equiatomic alloy by ∼40%. The alloy was experimentally investigated at room and elevated temperatures, including in-situ tensile testing. The alloy was found to possess slightly lower strength compared to the equiatomic alloy at room temperature, however, exhibited excellent thermal strength up to 873K. Deformation twinning was observed after tensile testing at room temperature, primarily attributed to the reduced stacking fault energy (SFE), which was proven by a thermodynamic model for calculating the SFE. The softening behaviour at room temperature can be explained through solid solution hardening (SSH), whereby a modified approach to Labusch's model was used to calculate the SSH in reported alloys in this study within the Co–Cr–Fe–Mn–Ni system. The modified models for SFE and SSH are proposed to be implemented into high-throughput screening algorithms for accelerated alloy design towards specific mechanical properties.
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| 21. |
- Di Egidio, G., et al.
(författare)
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Dry sliding behavior of AlSi10Mg alloy produced by Laser-based Powder Bed Fusion : influence of heat treatment and microstructure
- 2023
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 516-517
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Tidskriftsartikel (refereegranskat)abstract
- The L-PBF AlSi10Mg alloy is widely used in the production of structural parts in the transportation sector. However, the high stresses caused by the severe operating conditions require an optimal combination of mechanical and tribological properties. This paper reports on the effect of optimized T5 heat treatment (direct artificial aging: 4 h at 160 °C) and novel T6 heat treatment (rapid solution: 10 min at 510 °C, followed by artificial aging: 6 h at 160 °C) on the tribological behavior of the L-PBF AlSi10Mg alloy. Dry sliding tests (ball-on-disk) were carried out using AlSi10Mg samples as rotating disks against an Al2O3 stationary ball. The optimized T5 led to the formation of a stable protective oxide layer well adherent on the worn surface, increasing the wear resistance of the alloy. In addition, the novel T6 improved wear resistance compared to conventional T6 due to microstructural refinement induced by shorter solutionizing. The sub-surface analysis of the wear tracks highlighted the higher cohesion between the more homogeneous and finer Si particles and the α-Al matrix, as well as the improved load-bearing support compared to the coarser microstructure induced by conventional T6. Therefore, the new T6 could be the optimal solution for high-performance components.
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| 22. |
- Di Egidio, Gianluca, et al.
(författare)
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Influence of Microstructure on Fracture Mechanisms of the Heat-Treated AlSi10Mg Alloy Produced by Laser-Based Powder Bed Fusion
- 2023
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 16:5
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Tidskriftsartikel (refereegranskat)abstract
- Few systematic studies on the correlation between alloy microstructure and mechanical failure of the AlSi10Mg alloy produced by laser-based powder bed fusion (L-PBF) are available in the literature. This work investigates the fracture mechanisms of the L-PBF AlSi10Mg alloy in as-built (AB) condition and after three different heat treatments (T5 (4 h at 160 °C), standard T6 (T6B) (1 h at 540 °C followed by 4 h at 160 °C), and rapid T6 (T6R) (10 min at 510 °C followed by 6 h at 160 °C)). In-situ tensile tests were conducted with scanning electron microscopy combined with electron backscattering diffraction. In all samples the crack nucleation was at defects. In AB and T5, the interconnected Si network fostered damage at low strain due to the formation of voids and the fragmentation of the Si phase. T6 heat treatment (T6B and T6R) formed a discrete globular Si morphology with less stress concentration, which delayed the void nucleation and growth in the Al matrix. The analysis empirically confirmed the higher ductility of the T6 microstructure than that of the AB and T5, highlighting the positive effects on the mechanical performance of the more homogeneous distribution of finer Si particles in T6R.
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| 23. |
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| 24. |
- Dini, Hoda, 1984-, et al.
(författare)
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Optimization and validation of a dislocation density based constitutive model for as-cast Mg-9%Al-1%Zn
- 2018
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 710, s. 17-26
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Tidskriftsartikel (refereegranskat)abstract
- A dislocation density-based constitutive model, including effects of microstructure scale and temperature, was calibrated to predict flow stress of an as-cast AZ91D (Mg-9%Al-1%Zn) alloy. Tensile stress-strain data, for strain rates from 10-4 up to 10-1 s-1 and temperatures from room temperature up to 190 °C were used for model calibration. The used model accounts for the interaction of various microstructure features with dislocations and thereby on the plastic properties. It was shown that the Secondary Dendrite Arm Spacing (SDAS) size was appropriate as an initial characteristic microstructural scale input to the model. However, as strain increased the influence of subcells size and total dislocation density dominated the flow stress. The calibrated temperature-dependent parameters were validated through a correlation between microstructure and the physics of the deforming alloy. The model was validated by comparison with dislocation density obtained by using Electron Backscattered Diffraction (EBSD) technique.
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| 25. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
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Dynamic precipitation at elevated temperatures in a dual-phase AlCoCrFeNi high-entropy alloy : an in situ study
- 2018
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Ingår i: Philosophical Magazine Letters. - : Taylor & Francis. - 0950-0839 .- 1362-3036. ; 98:9, s. 400-409
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a possible phase transformation or precipitation of the face-centred cubic (FCC) phase on intermediate-temperature deformation of a dual-phase AlCoCrFeNi high-entropy alloy has been studied using in situ tensile testing at 550°C. Electron backscatter diffraction (EBSD) results showed localised precipitation of the FCC phase during the intermediate-temperature deformation. The overall fracture behaviour and crack propagation of the material was not altered much compared to the room-temperature behaviour, namely brittle trans-granular fracture. Deformation at higher temperatures (above 750°C) is suggested as a way to enhance the dynamic FCC phase precipitation, in order to improve the ductility or deformability of the alloy.
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| 26. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
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Effect of cold-work on the Hall–Petch breakdown in copper based micro-components
- 2015
-
Ingår i: Mechanics of materials. - : Elsevier. - 0167-6636 .- 1872-7743. ; 80, part A, s. 124-135
-
Tidskriftsartikel (refereegranskat)abstract
- Effects of substructural dimensions on the mechanical properties of micro-pins produced by an open-die micro-extrusion/forging process were studied. Micro-pins of diameter 0.3 mm were manufactured from copper strips, having different initial grain sizes. Micro-compression tests on the micro-pins revealed no significant size effect, even if the number of grains over the diameter of the micro-pins falls below its critical value. However, relaxation of the as-formed substructure using recovery annealing led to a surprising drop in the flow stress of the micro-pins. This was explained and attributed to the number of subgrains over the diameter of the micro-pins, showing the important role of subgrains rather than grains in determining the mechanical properties.
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| 27. |
- Ghassemali, Ehsan, 1983-
(författare)
-
Forging of Metallic Parts and Structures
- 2022
-
Ingår i: Encyclopedia of Materials. - Oxford : Elsevier. - 9780128197332 ; , s. 129-143
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Even with the wide applications of many new and modern manufacturing technologies, metal forming processes are still in great demand in many industrial sectors, ranging from transportation to medical applications. In this article, the basic knowledge in metal forming and specifically forging, which is one of the most commonly used processes for metal component manufacturing, is summarized. The effect of material behavior on the forming processes is discussed in detail. The classical modeling techniques to describe the forming processes are briefly introduced, with a focus on the challenges in this area. Different categories of forging process such as open-die, closed-die or cold, warm and hot forging are explained. Advantages of forging processes such as near-net-shape characteristics, microstructural refinement during the process, and relative ease of post-processing for forged parts are elaborated. Main disadvantages of forging include possible oxidation during hot forging, limitation on material selection for forging (workability), and the related maintenance cost of the forging tools. Examples of parts and structures that can be produced by forging process are metallic tools for various applications ranging from household to aerospace sectors, where close tolerance and proper mechanical properties are expected.
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| 28. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
Hall-Petch Equation in a Hypoeutectic Al-Si Cast Alloy : Grain Size vs. Secondary Dendrite Arm Spacing
- 2017
-
Ingår i: Procedia Engineering. - : Elsevier. ; , s. 19-24
-
Konferensbidrag (refereegranskat)abstract
- The Al-Si cast alloy family is widely used in the production of complex castings for various applications and known for its very good castability and high strength-to-weight ratio. However, early cracking under tensile loading is sometimes a limiting factor. Among other parameters, it is yet controversial whether grain boundaries are dominant strengthening factor in cast alloys, instead of dendrite/eutectic boundaries. This study presents the effect of secondary dendrite arm spacing (SDAS) and grain size on crack initiation and propagation of Al-Si cast alloys under tensile loading. The Al-10Si (wt.%) alloy with modified Si morphology was cast using inoculants (Al-5Ti-B master alloy) under different cooling rates to obtain a range of grain sizes (from below 138 μm to above 300 μm) and SDAS (6, 15 and 35 μm). Conventional tensile test as well as in-situ tensile test in a scanning electron microscope, equipped with an electron backscatter diffraction (EBSD) was carried out to understand the deformation mechanisms of the alloy. Observation of slip bands within the dendrites showed that in modified Si structure, the interdendritic (eutectic) area takes more portion of the strain during plastic deformation. Besides, only a few cracks were initiated at the grain boundaries; they were mostly initiated from dendrite/eutectic interface. All cracks propagated trans-granularly. Hall-Petch calculations also showed a strong relationship between SDAS and flow stress of the cast alloy. Although statistically correct, there was no physically meaningful relationship between the grain size and the flow stress. Nevertheless, formation of identical slip bands in each grain could be an evidence for the marginal effect of the grain size on the overall strength development of the alloy. Consequently, among other effects, the combinational dominant effect of SDAS and modest effect of grain size shall be considered for modification of the Hall-Petch equation for precise prediction of mechanical properties of cast alloys.
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| 29. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
High-Throughput CALPHAD : A Powerful Tool Towards Accelerated Metallurgy
- 2022
-
Ingår i: Frontiers in Materials. - : Frontiers Media S.A.. - 2296-8016. ; 9
-
Forskningsöversikt (refereegranskat)abstract
- Introduction of high entropy alloys or multi-principal element alloys around 15 years ago motivated revising conventional alloy design strategies and proposed new ways for alloy development. Despite significant research since then, the potential for new material discoveries using the MPEA concept has hardly been scratched. Given the number of available elements and the vastness of possible composition combinations, an unlimited number of alloys are waiting to be investigated! Discovering novel high-performance materials can be like finding a needle in a haystack, which demands an enormous amount of time and computational capacity. To overcome the challenge, a systematic approach is essential to meet the growing demand for developing novel high-performance or multifunctional materials. This article aims to briefly review the challenges, recent progress and gaps, and future outlook in accelerated alloy development, with a specific focus on computational high-throughput (HT) screening methods integrated with the Calculation of Phase Diagrams (CALPHAD) technique. Copyright © 2022 Ghassemali and Conway.
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| 30. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
On the Formation of Micro-Shrinkage Porosities in Ductile Iron Cast Components
- 2018
-
Ingår i: Metals. - : MDPI. - 2075-4701. ; 8:7
-
Tidskriftsartikel (refereegranskat)abstract
- A combination of direct austempering after solidification (DAAS) treatment and electron backscatter diffraction (EBSD) method was used to study the formation of micro-shrinkage porosities in ductile iron. Analyzing the aus-ferritic microstructure revealed that most of micro-shrinkage porosities are formed at the retained austenite grain boundaries. There was no obvious correlation between the ferrite grains or graphite nodules and micro-shrinkage porosities. Due to the absolute pressure change at the (purely) shrinkage porosities, the dendrite fragmentation rate during the DAAS process would be altered locally, which caused a relatively finer parent-austenite grain structure near such porosities.
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| 31. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
Revisiting the graphite nodule in ductile iron
- 2019
-
Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 161, s. 66-69
-
Tidskriftsartikel (refereegranskat)abstract
- The growth mechanism of graphite nodules in ductile iron was experimentally investigated using high-resolution 3D tomography of an individual graphite nodule in a near-eutectic ductile iron. The dual beam scanning electron microscopy (FIB-SEM) technique was used for this purpose. Iron particles elongated in the radial direction were observed inside a graphite nodule. Some micro-voids were detected inside the nodule, mostly located at the end of the iron particles. These observations were compared with established theories about the growth of graphite nodules and iron entrapment/engulfment in between the graphite sectors during solidification of ductile iron.
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| 32. |
- Ghatei-Kalashami, A., et al.
(författare)
-
Liquid metal embrittlement cracking behavior in iron-zinc (Fe/Zn) couple : Comparison of ferritic and austenitic microstructures
- 2022
-
Ingår i: Materials letters (General ed.). - : Elsevier. - 0167-577X .- 1873-4979. ; 324
-
Tidskriftsartikel (refereegranskat)abstract
- Liquid metal embrittlement (LME) has emerged as a major concern when developing high-strength automotive steels. However, information regarding the impact of initial microstructure on LME severity is limited in the Fe/Zn couple. Specifically, there is no consensus as to which ferritic and austenitic microstructures are more susceptible to LME cracking. The present study aims to examine the LME cracking behavior of fully ferritic and austenitic microstructures under the same thermomechanical conditions. It was shown that the ferritic microstructure has a higher sensitivity to LME crack initiation, whereas the austenitic specimen displayed a much longer average crack length, which indicates higher crack propagation rate than the ferritic specimen. It has been determined that in-situ austenite to ferrite transformations during Zn diffusion, as well as grain boundary segregation of alloying elements such as Cr and Ti, contribute to the LME propagation rate.
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| 33. |
- Ghatei-Kalashami, A., et al.
(författare)
-
Occurrence of liquid-metal-embrittlement in a fully ferritic microstructure
- 2021
-
Ingår i: Materialia. - : Elsevier. - 2589-1529. ; 15
-
Tidskriftsartikel (refereegranskat)abstract
- Despite numerous studies making an effort to attain a thorough understanding of the liquid-metal-embrittlement (LME) phenomenon, the metallurgical facet of this catastrophic event remains unclear in iron/zinc (Fe/Zn) systems. While it has been frequently reported that the presence of austenite is an essential prerequisite for LME formation, the present study showed that fully ferritic structure is prone to LME phenomenon and has a high susceptibility to LME-cracking which makes it a novel observation adding to a pool of knowledge regarding LME occurrence. The elemental distribution analysis near the LME crack-tip indicated that liquid Zn was not present which confirmed solid-state grain boundary diffusion was a plausible description of LME-cracking. The occurrence of grain dropout as well as a Zn-containing crack in grain boundary without any branches with other cracks showed that grain boundary sensitization has assisted LME-cracking.
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| 34. |
- Hajiannia, Iman, et al.
(författare)
-
A microstructure evaluation of different areas of resistance spot welding on ultra-high strength TRIP1100 steel
- 2018
-
Ingår i: Cogent Engineering. - : Cogent OA. - 2331-1916. ; 5:1
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the microstructure of resistance spot welds of advanced ultra-high strength TRIP1100 steel was investigated. For this purpose, welding was performed after determining the best welding parameters. Four sections of the heat-affected zone (HAZ) regions were selected in the regions where the heat exchange was used to control the microstructure. Then, they were used with EBSD by scanning electron microscopy (SEM). The results showed that the TRIP1100 steel microstructure consisted of polygonal ferrites, bainites, residual austenite (RA) and martensite/austenitic islands (M/A). They also showed that the melting zone (FZ) has a lath martensite structure, and the grains are larger in packets. The structure of the martensite and different orientation grains are located in the Upper-critical area (UCHAZ). In the inter-critical region (ICHAZ), the high carbon martensitic content is higher due to the presence and the structure of ferrite and martensite. In the sub-critical region (SCHAZ), due to the tempering of martensite at a temperature below A(C1), the structure is similar to the base metal (BM), with the difference that the RA degradation reduces its structure by 50%. It was found that the RA in the BM had completely transformed. The results showed that with the movement of the BM to the weld metal, the boundaries with a low angle were increased.
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| 35. |
- Hajiannia, I., et al.
(författare)
-
Development of Ultrahigh Strength TRIP Steel Containing High Volume Fraction of Martensite and Study of the Microstructure and Tensile Behavior
- 2018
-
Ingår i: Transactions of the Indian Institute of Metals. - : Springer. - 0972-2815 .- 0975-1645. ; 71:6, s. 1360-1367
-
Tidskriftsartikel (refereegranskat)abstract
- A new transformation induced plasticity (TRIP) steel containing high volume fraction of martensite was produced by austempering heat treatment cycle. Microstructure and tensile properties of this TRIP steel were investigated and compared to those of a dual phase (DP) steel with high martensite volume fraction. Microstructural analysis showed a mixture of ferrite, bainite, retained austenite and about 25–30 vol% of martensite in the TRIP steel. As a result of the strain induced transformation of retained austenite to martensite, the TRIP steel showed a strength elongation balance of 86% higher than that for the DP steel. In comparison to the commercial TRIP780 steel, the current TRIP steel showed a 15% higher ultimate tensile strength value while maintaining the same level of ductility. TRIP steel also had a larger work hardening exponent than DP steel at all strains.
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| 36. |
- Hajiannia, Iman, et al.
(författare)
-
The assessment of second pulse effects on the microstructure and fracture behavior of the resistance spot welding in advanced ultrahigh-strength steel TRIP1100
- 2019
-
Ingår i: Iranian Journal of Materials Science and Engineering. - : Iran University of Science and Technology. - 1735-0808. ; 16:2, s. 79-88
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the effects of the second pulse resistance spot welding on the microstructure and mechanical properties of transformation induced plasticity 1100 steel were evaluated. The thermal process after welding was designed to improve metallurgical properties with pulse currents of 6 kA, 9 kA, and 12 kA after initial welding with 10 kA current. The effect of the second pulse on mechanical and microstructural properties was investigated. The fracture of the welds was for pulsed samples of 6 kA and 9 kA pull out with mechanical test. Due to the existence of the microstructure including the equiaxial dendritic and finer in fusin zone in the pulsed current of 9 kA, the maximum fracture energy, and maximum force were observed. A significant decrease in the FZ hardness in 6 kA current was observed in the nano-hardness results, which was attributed to the existence of martensitic and ferrite temper. The highest ratio of CTS/TSS was obtained for 6 kA and 9 kA, respectively, and force-displacement evaluation was maximum in 9 kA. The fracture surfaces included dendrites and dimples. The results of partial fracture revealed separation in the coherent boundaries of the coarse grain of the annealed region.
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| 37. |
- Hernando, Juan Carlos, et al.
(författare)
-
The effect of coarsening of primary austenite on the ultimate tensile strength of hypoeutectic compacted graphite Fe-C-Si alloys
- 2019
-
Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 168, s. 33-37
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of primary austenite morphology on the ultimate tensile strength (UTS) of hypoeutectic compacted graphite Fe-C-Si alloys (CGI) is studied by isothermal coarsening experiments. Secondary dendrite arm spacing (SDAS) and the morphological characteristics related to the surface area of primary austenite, M γ and D ID Hyd , increase with the cube root of coarsening time. UTS decreases linearly with increasing coarseness of primary austenite. The eutectic and eutectoid microstructures are unaffected by the primary austenite morphology. These observations demonstrate the strong influence of primary austenite morphology on the mechanical properties of hypoeutectic CGI alloys.
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| 38. |
- Hernando, Juan Carlos, et al.
(författare)
-
The morphological evolution of primary austenite during isothermal coarsening
- 2017
-
Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 131, s. 492-499
-
Tidskriftsartikel (refereegranskat)abstract
- The morphological evolution of primary austenite in an industrial hypoeutectic lamellar cast iron was studied under isothermal conditions for coarsening times varying from 0 min to 96 h. The dendritic austenite structure formed during the primary solidification suffered major morphological changes during the isothermal coarsening process. After a sufficient coarsening time, dendrite fragmentation, globularization, and coalescence of austenite were studied using electron backscatter diffraction (EBSD) technique. This study confirmed that the secondary dendrite arm spacing (SDAS) is an inappropriate length scale to describe the primary austenite coarsening process for longer times. The application of shape independent quantitative parameters confirmed the reduction of the total interfacial area during microstructural coarsening. The modulus of the primary austenite, Mγ, which represents the volume-surface ratio for the austenite phase, and the spatial distribution of the austenite particles, measured as the nearest distance between the center of gravity of neighboring particles, Dγ, followed a linear relation with the cube root of coarsening time during the whole coarsening process. The mean curvature of the austenite interface, characterized through stereological relations, showed a linear relation to Mγ and Dγ, allowing the quantitative characterization and modeling of the complete coarsening process of primary austenite.
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| 39. |
- Hernando, Juan Carlos, et al.
(författare)
-
The role of primary austenite morphology in hypoeutectic compacted graphite iron alloys
- 2020
-
Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 14:3, s. 745-754
-
Tidskriftsartikel (refereegranskat)abstract
- This work investigates the role of primary austenite morphology on the eutectic and eutectoid microstructures and the ultimate tensile strength (UTS) in a hypoeutectic compacted graphite iron (CGI) alloy. The morphology of primary austenite is modified by isothermal coarsening experiments in which holding times up to 60 min are applied to the solid–liquid region after coherency. The cooling conditions for the subsequent eutectic and eutectoid reactions are similar. Miniaturized tensile tests are performed to evaluate the UTS. The morphological characteristics related to the surface area of primary austenite, the modulus of primary austenite, Mγ, and the hydraulic diameter of the interdendritic region, DHydID, increase with the cube root of coarsening time. The eutectic and eutectoid microstructures are not significantly affected by the morphology of primary austenite, thus indicating that the morphology of the interdendritic regions does not control the nucleation frequency and growth of eutectic cells or graphite. UTS decreases linearly with the increasing coarseness of primary austenite for similar eutectic and eutectoid microstructures, demonstrating the strong influence of primary austenite morphology on the UTS in hypoeutectic CGI alloys.
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| 40. |
- Jandaghi, Mohammad Reza, et al.
(författare)
-
Additive manufacturing of nano-oxide decorated AlSi10Mg composites : A comparative study on Gd2O3 and Er2O3 additions
- 2022
-
Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 192
-
Tidskriftsartikel (refereegranskat)abstract
- AlSi10Mg-based nanocomposites were fabricated by laser powder bed fusion (LPBF) additive manufacturing with the addition of 1 wt% Gd2O3 and Er2O3 nanoparticles. The effect of different process parameters and supplementary remelting on the densification of the samples was evaluated. Results showed that remelting the printed layers could improve the densification. According to the microstructural observations, stacking the nanoparticles on uneven surfaces of irregular AlSi10Mg particles beside van der Waals's attractive force between the adjacent particles eventually forms coarsened clusters in printed samples. The XRD patterns disclosed the partial reaction between the nano-oxides and the aluminum matrix and the formation of some interfacial intermetallic layers, which were also validated by SEM characterization. The measurement of grain size and microhardness implied that the addition of Er2O3 played a more effective role in grain refinement and enhanced the hardness more uniformly compared to Gd2O3. Overall, the acquired average hardness for both nano-oxide reinforced specimens was greater than the reported values for LPBF-fabricated AlSi10Mg-matrix composites in the past. EBSD analyses revealed that due to the pinning effect of the nanoparticles, particle-rich zones demonstrated higher KAM and grain orientation spread (GOS) values which were attributed to the formation of more GNDs at the matrix/particles interfaces.
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| 41. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(författare)
-
Characterization and modeling of the mechanical behavior of high silicon ductile iron
- 2017
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 708, s. 159-170
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the effect of the solidification conditions and silicon content on the mechanical properties of ductile iron and presents empirical models for predicting the tensile behavior based on the microstructural characterizations. Two ductile iron grades of GJS-500-7 and GJS-500-14 were cast with silicon content of 2.36% and 3.71%, respectively. The cast geometry consisted of six plates with different thicknesses that provided different cooling rates during the solidification. Microstructure analysis, tensile and hardness tests were performed on the as-cast material. Tensile behavior was characterized by the Ludwigson equation. The tensile fracture surfaces were analyzed to quantify the fraction of porosity. The results showed that graphite content, graphite nodule count, ferrite fraction and yield strength were increased by increasing the silicon content. A higher silicon content resulted in lower work hardening exponent and strength coefficient on the Ludwigson equation. The results for 0.2% offset yield and the Ludwigson equation parameters were modeled based on microstructural characteristics, with influence of silicon content as the main contributing factor. The models were implemented into a casting process simulation to enable prediction of microstructure-based tensile behavior. A good agreement was obtained between measured and simulated tensile behavior, validating the predictions of simulation in cast components with similar microstructural characteristics.
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| 42. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(författare)
-
Effect of Boron and Cross-Section Thickness on Microstructure and Mechanical Properties of Ductile Iron
- 2018
-
Ingår i: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 925, s. 249-256
-
Tidskriftsartikel (refereegranskat)abstract
- Eeffect of Boron addition on the microstructure and mechanical properties of ductile iron, GJS-500-7 grade was studied. Three cast batches with the Boron content of 10, 49 and 131ppm were cast in a casting geometry containing plates with thicknesses of 7, 15, 30, 50 and 75mm. Microstructure analysis, tensile test, and hardness test were performed on the samples which were machined from the casting plates. Addition of 49 ppm Boron decreased pearlite fraction by an average of 34±6% in all the cast plates. However, minor changes were observed in the pearlite fraction by increasing Boron from 49 to 131 ppm. Variation in the plate thickness did not affect the pearlite fraction. The 0.2% offset yield and ultimate tensile strength was decreased by an average of 11±1% and 18±2%, respectively. Addition of 49 ppm Boron decreased Brinell hardness by 16±1%, while 11±2% reduction was obtained by addition of 131ppm Boron.
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| 43. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(författare)
-
Microstructural strain mapping during in-situ cyclic testing of ductile iron
- 2018
-
Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 140, s. 333-339
-
Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on local strain distribution in the microstructure of high silicon ductile iron during cyclic loading. In-situ cyclic test was performed on compact-tension (CT) samples inside the scanning electron microscope (SEM) to record the whole deformation and obtain micrographs for microstructural strain measurement by means of digital image correlation (DIC) technique. Focused ion beam (FIB) milling was used to generate speckle patterns necessary for DIC measurement. The equivalent Von Mises strain distribution was measured in the microstructure at the maximum applied load. The results revealed a heterogeneous strain distribution at the microstructural level with higher strain gradients close to the notch of the CT sample and accumulated strain bands between graphite particles. Local strain ahead of the early initiated micro-cracks was quantitatively measured, showing high strain localization, which decreased by moving away from the micro-crack tip. It could be observed that the peak of strain in the field of view was not necessarily located ahead of the micro-cracks tip which could be because of the (i) strain relaxation due to the presence of other micro-cracks and/or (ii) presence of subsurface microstructural features such as graphite particles that influenced the strain concentration on the surface.
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| 44. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(författare)
-
Strain localization and crack formation effects on stress-strain response of ductile iron
- 2017
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 702, s. 265-271
-
Tidskriftsartikel (refereegranskat)abstract
- The strain localization and crack formation in ferritic-pearlitic ductile iron under tension was investigated by in-situ tensile tests. In-situ tensile tests under optical microscope were performed and the onset of the early ferrite-graphite decohesions and micro-cracks inside the matrix were studied. The results revealed that early ferrite-graphite decohesion and micro-cracks inside the ferrite were formed at the stress range of 280–330 MPa, where a kink occurred in the stress-strain response, suggesting the dissipation of energy in both plastic deformation and crack initiation. Some micro-cracks initiated and propagated inside the ferrite but were arrested within the ferrite zone before propagating in the pearlite. Digital Image Correlation (DIC) was used to measure local strains in the deformed micrographs obtained from the in-situ tensile test. Higher strain localization in the microstructure was measured for the areas in which the early ferrite-graphite decohesions occurred or the micro-cracks initiated. © 2017 Elsevier B.V.
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| 45. |
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| 46. |
- Keller, Christina, 1961-, et al.
(författare)
-
Teacher roles in a blended learning materials engineering master program : "It's not a new role, it's a new way!"
- 2017
-
Konferensbidrag (refereegranskat)abstract
- Engineering education are characterized by laboratories, mathematical foundations and design tools. These pillars of engineering education do not seem to be ideal for online education as the field lags behind other fields in adopting online education. Laboratories are for instance hard to implement online due to the need of direct operation of instruments. Likewise, course materials requiring use of mathematics have traditionally not been as easy to implement as topics that require only text-based instructions (Bourne et al., 2005). Real laboratory sessions have also shown to be more motivated for engineering students than virtual simulations (Stefanovic, 2013). In spite of this, there are increasing evidence of use of blended and online learning in engineering education. For example, online self-study environment to supplement the classroom instruction in engineering courses in graphical communication (Sun et al., 2014), virtual laboratories and simulation environments (Balamuraithara & Woods, 2007; Bourne et al., 2005) and online platforms for developing learning networks for global engineering (Meikleham et al. 2015). The School of Engineering at Jönköping University, the Swedish foundry association, the research institute Swerea/SWECAST and twelve foundry industries cooperate to develop a blended learning one-year master program in product development in materials and manufacturing. As previously performed courses have been given on campus, teachers needed to take on new roles as blended learning teachers. In this paper, we present the initial results from a study that aims to investigate the perceived roles of university teachers in a blended learning materials engineering master program.
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| 47. |
- Khorshidi, H., et al.
(författare)
-
Design of a hot deformation processing map for a Ni-free, N-bearing austenitic stainless steel
- 2021
-
Ingår i: Materials Today Communications. - : Elsevier. - 2352-4928. ; 27
-
Tidskriftsartikel (refereegranskat)abstract
- The hot deformation characteristics of a FeCrMnN austenitic stainless steel containing 0.28 wt.% nitrogen (N) was investigated by hot compression tests using a Gleeble simulator in the temperature range of 800-1200 degrees C and at constant true strain rates of 0.01-10 s(-1) with all specimens deformed to similar to 0.9 true strain. The influence of deformation conditions on microstructural mechanisms and phase transformations was characterized. A processing map based on dynamic materials modelling (DMM) was designed and interpreted for predicting the domain of stable flow for safe, defect-free hot deformation. The results revealed the occurrence of dynamic recrystallization (DRX) in a domain extending over the temperature and strain rate ranges of 1100-1200 degrees C and 0.1-1 s(-1), respectively, with the efficiency of power dissipation (eta) of 45-55 %. Decreasing temperature and increasing strain rate led to a reduction in DRX grain size following microstructural reconstitution. Another small deterministic domain of 820-1000 degrees C and 0.01-0.05 s(-1) was identified showing occurrence of partial DRX in shear bands leading to formation of a mixed microstructure. The instability criteria delineated the regime of unstable flow covering a large part of the processing map extending over low temperatures (800-950 degrees C) and high strain rates (0.1-10 s(-1)) that must be avoided during processing.
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| 48. |
- Mazaheri, Y., et al.
(författare)
-
On the simultaneous improving of strength and elongation in dual phase steels via cold rolling
- 2020
-
Ingår i: Metals. - : MDPI. - 2075-4701. ; 10:12, s. 1-16
-
Tidskriftsartikel (refereegranskat)abstract
- The ferrite-pearlite microstructure was cold-rolled to form dual phase (DP) steels, the percentage reduction of which varied. To do so, the steels were annealed in two steps and then the workpiece underwent water quenching. Accordingly, a decrease was observed in the average size of the ferrite grains, from above 15 µm to below 2 µm, subsequent to the thermomechanical processing. By an increase in the reduction percentage, the volume fraction of martensite grew. The balance between strength and elongation also improved nearly 3 times, equivalent to approximately 37,297 MPa% in DP in comparison to 11,501 MPa% in the ferrite-pearlite microstructure, even after 50% cold-rolling. Based on Hollomon and differential Crussard-Jaoul (DC–J) analyses, the DP steels under investigation deformed in two and three stages, respectively. The modified C–J (MC–J) analysis, however, revealed that the deformation process took place in four stages. The rate of strain hardening at the onset of the deformation process was rather high in all DP steels. The given rate increased once the size of the ferrite grains reduced; an increase in the volume fraction of martensite due to larger percentage of reduction also contributed to the higher rate of strain hardening. The observation of the fractured surfaces of the tensile specimens indicated ductile fracture of the studied DP steels.
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| 49. |
- Mohammadi Zahrani, M., et al.
(författare)
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Microstructure evolution and mechanical properties of laser-welded joints of 1.2 GPa-class quenching and partitioning steel
- 2024
-
Ingår i: Optics and Laser Technology. - : Elsevier. - 0030-3992 .- 1879-2545. ; 170
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Tidskriftsartikel (refereegranskat)abstract
- Laser welding of 1.2 GPa-class cold-rolled quenching and partitioning steel with martensite + retained austenite microstructure was performed at different heat inputs ranging from 91–240 J·mm−1 using a CO2 laser. Scanning electron microscopy, electron backscatter diffraction, and uniaxial tensile testing equipped with digital image correlation were employed to characterize the microstructural and mechanical evolution of the joints. The results revealed that the fusion zone and upper-critical HAZ comprised full martensite with high microhardness. The HAZ contained a narrow softened zone with a minimum width of ∼0.6 µm and at least 48 HV microhardness drop because of the martensite tempering. Martensite decomposition and precipitation of carbides were noticeable at higher heat inputs, so that the hardness of the softened zone was declined. At the welding heat input of 91 J·mm−1, the yield and tensile strengths were 841 and 1270 MPa, respectively, which represented reductions of 5.5 and 0.78% compared to the base material properties. The joint efficiency of 99.2% was achieved at the lowest heat input. The tensile deformation was primarily concentrated in the softened zone and was small in the fusion zone. However, the participation of the base material to tensile deformation was enhanced at lower heat inputs, leading to higher elongation values up to ∼11.9% during tensile testing.
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