| 1. |
- 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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| 2. |
- 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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| 3. |
- 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
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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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| 4. |
- Ghassemali, Ehsan, 1983-
(författare)
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Forging of Metallic Parts and Structures
- 2022
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Ingår i: Encyclopedia of Materials. - Oxford : Elsevier. - 9780128197332 ; , s. 129-143
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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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| 5. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
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High-Throughput CALPHAD : A Powerful Tool Towards Accelerated Metallurgy
- 2022
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Ingår i: Frontiers in Materials. - : Frontiers Media S.A.. - 2296-8016. ; 9
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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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| 6. |
- Ghatei-Kalashami, A., et al.
(författare)
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Liquid metal embrittlement cracking behavior in iron-zinc (Fe/Zn) couple : Comparison of ferritic and austenitic microstructures
- 2022
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Ingår i: Materials letters (General ed.). - : Elsevier. - 0167-577X .- 1873-4979. ; 324
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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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| 7. |
- Jandaghi, Mohammad Reza, et al.
(författare)
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Additive manufacturing of nano-oxide decorated AlSi10Mg composites : A comparative study on Gd2O3 and Er2O3 additions
- 2022
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Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 192
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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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| 8. |
- Pinate, Santiago, et al.
(författare)
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Strengthening mechanisms and wear behavior of electrodeposited Ni–SiC nanocomposite coatings
- 2022
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Ingår i: Journal of Materials Science. - : Elsevier. - 0022-2461 .- 1573-4803. ; 57:35, s. 16632-16648
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Tidskriftsartikel (refereegranskat)abstract
- The present paper describes the study of the synergism between the matrix microstructure and reinforcement phase in electrodeposited nanocomposite coatings. Adding hard nanoparticles into the metallic matrix leads to hardening of the coating. The effects of particle load, size and dispersion on hardening as well as their influence on metal microstructure refinement were studied. The relative contributions of strengthening factors in Ni/nano-SiC composites, namely, Hall–Petch strengthening, Orowan strengthening, enhanced dislocation density and particles incorporation, were evaluated. The production of various coatings under different stirring conditions and powders resulted in dissimilarities in the incorporation of particles. The Hall–Petch relationship for pure nickel was determined using samples produced under different current densities. Additionally, the grain refinement resulting from the particle codeposition and agitation mode were identified as influential factors in grain-size strengthening. Dislocation density strengthening was significant in electrodeposits produced using ultrasonic agitation, while it was negligible in layers produced under other conditions. Particles codeposition affected the magnitude of Orowan strengthening, resulting in cases where strengthening was negligible despite the presence of particles. The sum of contributions and the modified Clyne methods were used to calculate the hardness of the composites based on the contribution of each strengthening factor, and the calculation results were in good agreement with experimental data. The wear behavior of the composites was analyzed by pin-on-disk measurements, and the results correlated with the strengthening mechanisms. Particle size, dispersion and content increased the strengthening effects as well as the hardness and wear resistance of the coatings.
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| 9. |
- Sainis, Salil
(författare)
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An Insight into the Critical Role of Microstructure and Surface Preparation on Localized Conversion Coating Deposition on Cast Al Alloys
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The spontaneous cerium conversion coating formation over aluminium alloys is affected by the chemical process conditions, the surface preparation prior to conversion treatment and the microstructure of the underlying alloy. Most research performed until now focus only on the former whereas the influence of the latter two is poorly understood. The microstructure of aluminium alloys contains cathodic intermetallic particles that have a crucial role in conversion coating formation as they are responsible for the increase in pH to a critical level where chemical precipitation reaction of conversion coating compounds becomes possible. There are many different types of intermetallics in the aluminium alloys’ microstructure whose cathodic potential depends on their chemical composition, but no systematic study exists on the influence of their geometric properties on the reactivity of intermetallics. The surface preparation also critically affects reactivity of intermetallics, and a consensus exists regarding which preparation procedure makes an alloy surface most conducive for conversion coating deposition, but little is known about the topographical and volta potential changes occurring around the intermetallics from the surface preparations. An insight into both the role of microstructure and surface preparation is thus crucial as they can help design better treatments.To address this knowledge gap, model microstructures of hypoeutectic cast Al-7Si alloys have been created in the study with the desired intermetallic composition and geometry. By addition of Cu and Fe to the hypoeutectic cast alloy, two types of intermetallics, namely θ-Al2Cu and β-Al5FeSi form and are the main objects of investigation in the study. The geometrical dimensions of the intermetallics were modified by directionally solidifying the cast alloys at different rates. Different surface preparation procedures, namely mechanical polishing, NaOH, NaOH-HNO3 and NaOH-H2SO4 have been tried in the study. Furthermore, parameters such as etching time have been varied to understand their influence. The microstructural features, particularly intermetallic geometry and cathodic potential have been systematically compared with localized deposition on them through conversion coating treatment. Experimentally derived data-based analyses have been conducted to come to conclusions in the study.Firstly, the study found differences in the initiation of localized deposits on θ-Al2Cu and β-Al5FeSi attributed this to the conductivity variation due to compositional difference. Among the three differently sized θ-IM investigated in the study, namely fine, coarse and bulky θ, increasing the size from fine to coarse led to increase in reactivity of the IM for localized deposition. But increasing the size even further from coarse to bulky θ decreased the reactivity. Such a decrease in reactivity was found to be due to a combination of factors such as volta potential difference relative to the matrix and geometry.Surface preparation affected localized deposition and the choice of procedure applied critically depends on the intermetallics present in the microstructure. The β-Al5FeSi is most reactive for conversion coating deposition when prepared with NaOH etching solution but becomes passive when further pickled with HNO3 solution. The θ-Al2Cu, on the other hand, becomes most active when subjected to multi-step NaOH- HNO3 procedure. Such observations make the choice of a surface preparation procedure difficult when the alloy microstructure contains both θ-Al2Cu and β-Al5FeSi intermetallics. The localized deposition of cerium conversion compounds after surface preparation are triggered due to a combination of surface factors like including volta potential and presence of Al(OH)3 smut, with varying degrees of dominance depending on the type of IM. Al(OH)3 smut content was found sensitive to the NaOH etching time. A further HNO3 pickling step cleans the surface. A “cleaner” surface was found to be associated with more consistent coverage numbers, while the presence of Al(OH)3 smut, on the one hand provides additional source of alkalinity, does not consistently result in good coverage.
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