| 1. |
- Ghasemi, Rohollah, 1983-, et al.
(författare)
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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. |
- 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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| 3. |
- 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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| 4. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
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On the Formation of Micro-Shrinkage Porosities in Ductile Iron Cast Components
- 2018
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 8:7
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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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| 5. |
- Hajiannia, Iman, et al.
(författare)
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A microstructure evaluation of different areas of resistance spot welding on ultra-high strength TRIP1100 steel
- 2018
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Ingår i: Cogent Engineering. - : Cogent OA. - 2331-1916. ; 5:1
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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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| 6. |
- Hajiannia, I., et al.
(författare)
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Development of Ultrahigh Strength TRIP Steel Containing High Volume Fraction of Martensite and Study of the Microstructure and Tensile Behavior
- 2018
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Ingår i: Transactions of the Indian Institute of Metals. - : Springer. - 0972-2815 .- 0975-1645. ; 71:6, s. 1360-1367
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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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| 7. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(författare)
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Effect of Boron and Cross-Section Thickness on Microstructure and Mechanical Properties of Ductile Iron
- 2018
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Ingår i: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 925, s. 249-256
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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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| 8. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(författare)
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Microstructural strain mapping during in-situ cyclic testing of ductile iron
- 2018
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Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 140, s. 333-339
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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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| 9. |
- Riestra, Martin, 1985-, et al.
(författare)
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Complexities in the assessment of melt quality
- 2018
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 12:3, s. 441-448
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Tidskriftsartikel (refereegranskat)abstract
- If high-performance aluminium castings are to be produced, the melt quality needs to be properly assured. Multiple tests for melt quality assessment exist and have previously been analysed. In most studies, the techniques were used separately. In this work, reduced pressure, fluidity, Prefil and tensile tests were evaluated. A commercial EN 46000 alloy was used as the base material with additions of 25 and 50 wt% machining chips to degrade the melt quality. In reduced pressure and fluidity tests, oxides floated to the top of samples, decreasing the reliability. Bifilm index increased with addition level, but not correspondingly. Density index, Prefil and fluidity tests did not present significant variations, and tensile properties only deteriorated with the 50 wt% addition level. The investigated techniques provided information, but measuring the melt quality reliably remains a challenge.
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| 10. |
- Sujakhu, S., et al.
(författare)
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On the fatigue damage micromechanisms in Si-solution-strengthened spheroidal graphite cast iron
- 2018
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Ingår i: Fatigue & Fracture of Engineering Materials & Structures. - : John Wiley & Sons. - 8756-758X .- 1460-2695. ; 41:3, s. 625-641
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Tidskriftsartikel (refereegranskat)abstract
- Graphite nodules in spheroidal graphite cast iron (SGI) play a vital role in fatigue crack initiation and propagation. Graphite nodules growth morphology can go through transitions to form degenerated graphite elements other than spheroidal graphite nodules in SGI microstructure. These graphite particles significantly influence damage micromechanisms in SGI and could act differently than spheroidal graphite nodules. Most of the damage mechanism studies on SGI focused on the role of spheroidal graphite nodules on the stable crack propagation region. The role of degenerated graphite elements on SGI damage mechanisms has not been frequently studied. In this work, fatigue crack initiation and propagation tests were conducted on EN-GJS-500-14 and observed under scanning electron microscope to understand the damage mechanisms for different graphite shapes. Crack initiation tests showed a dominant influence of degenerated graphite elements where early cracks initiated in the microstructure. Most of the spheroidal graphite nodules were unaffected at the early crack initiation stage, but few of them showed decohesion from the ferrite matrix and internal cracking. In the crack propagation region, graphite/ferrite matrix decohesion was the frequent damage mechanism observed with noticeable crack branching around graphite nodules and the crack passing through degenerated graphite elements. Finally, graphite nodules after decohesion acted like voids which grew and coalesced to form microcracks eventually causing rapid fracture of the remaining section.
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| 11. |
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| 12. |
- Wójcik, Natalia A., et al.
(författare)
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Influence of synthesis conditions on glass formation, structure and thermal properties in the Na2O-CaO-P2O5 system doped with Si3N4 and Mg
- 2018
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier. - 0022-3093 .- 1873-4812. ; 494, s. 66-77
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Tidskriftsartikel (refereegranskat)abstract
- Oxynitride phosphate glasses and glass-ceramics were prepared using new synthesis routes for phosphate glasses. Materials were melted from pre-prepared glass samples in the system Na-Ca-P-0 with addition of Mg and/or Si3N4 powders under different preparation conditions. The melting process was conducted at 1000-1500 degrees C either under air or nitrogen atmosphere to obtain materials with different nitrogen content. Their topography and structure were characterized by Confocal Microscopy, Scanning Electron Microscopy, X-ray powder diffraction and Raman and infrared spectroscopy techniques, while their chemical compositions were examined by Energy Dispersive X-ray spectroscopy (EDS). All materials prepared under nitrogen atmosphere were found to contain a relative low quantity of nitrogen and high amount of Nb leached from the crucible. The reaction with the Nb crucible was not previously observed for silicon-based oxynitride glasses. The synthesized materials form two groups: glasses and glass-ceramics. The first ones, were prepared under air and nitrogen atmospheres at temperatures up to 1400 degrees C, and were found to be amorphous and homogeneous. Raman and infrared spectroscopy measurements confirm the presence of amorphous phosphates in the synthesized materials. The samples of the second group were prepared at temperatures above 1400 degrees C and were found to be translucent and partially crystallized. They contain nanocrystallites of calcium and sodium phosphates including hydroxyapatite (HAp). The thermal properties of samples were studied by Differential Scanning Calorimetry (DSC). The obtained glass transition temperatures range from about 360 degrees C to 640 degrees C and exhibit high values for glass-ceramic materials. Stability is improved in the studied glass-ceramics because of the increased degree of network polymerization of the remaining glassy matrix. The approximate fragility index decreases two times for oxynitride materials compared to the primary glass. The synthesized new materials may be competitive to well-known bioactive phosphate glasses thanks to their improved stability by Mg, Si, N and Nb doping.
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