| 1. |
- Banijamali, S. M., et al.
(författare)
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Effect of Ce Addition on the Tribological Behavior of ZK60 Mg-Alloy
- 2021
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Ingår i: Metals and Materials International. - : Springer. - 1598-9623 .- 2005-4149. ; 27:8, s. 2732-2742
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Tidskriftsartikel (refereegranskat)abstract
- The present work aims to study the tribological behavior of an extruded ZK60 alloy in the presence of Ce; in a previous study, among ZK60 alloys with different Ce addition rates, an alloy with 3 wt% of Ce was found to exhibit the most promising mechanical (e.g., hardness and strengths) properties, while its wear behavior remained unknown. The results of microstructural examinations by optical and electron microscopes show that Ce addition reduces the grain size from 6.1 to 2.0 μm. Besides, in addition to the precipitates already distributed in the base alloy (Mg7Zn3), Ce could promote the formation of a new precipitate (MgZn2Ce), increasing the total fraction of the precipitates. These microstructural evolutions enhance the strengths of the studied ZK60 alloy, as the yield and tensile strengths increase from 212 to 308 MPa and from 297 to 354 MPa, respectively. A pin on disc tribometer was employed to study the wear behavior of the developed alloy under different normal loads (5, 20, 40, and 60 N). The results show that the base and Ce-added alloys exhibit almost a similar frictional behavior, while the wear resistance of the Ce-added alloy is higher within the load ranges applied: (i) in low load conditions (5 and 20 N), where the abrasive wear is the active mechanism, the precipitates in the Ce-added alloy could enhance the wear resistance. (ii) Under the load of 40 N, oxidative wear is also an operative wear mechanism, leading to a sharp increase in the wear rate of the alloys. In this condition, Ce could provide a protective oxide layer, which could improve the wear resistance of the alloy. (iii) At a load of 60 N, both studied alloys exhibit a similar wear rate due to a severe oxidation condition. Therefore, beyond this loading condition, the microstructural evolutions (e.g., change in precipitation behavior) caused by Ce addition can no longer contribute to the enhancement of wear resistance.
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| 2. |
- Banijamali, Seyed Masih, et al.
(författare)
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Experimental and Simulation Study on Wear Behavior of ZK60 Alloy with 3 wt.% Yttrium Addition
- 2022
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Ingår i: Journal of materials engineering and performance (Print). - : Springer Nature. - 1059-9495 .- 1544-1024. ; 31:6, s. 4721-4734
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the effect of 3 wt.% of Y addition on the wear behavior of ZK60 extruded alloy was investigated using both experiment and simulation. First, a pin-on-disc tribometer was used to test dry sliding wear against an AISI 52100 steel counterface in a load range of 5-60 N. Microstructural study revealed that adding Y to ZK60 alloy resulted in substantial grain refinement and formation of new precipitates. The wear rate and friction coefficient were reduced with Y addition, attributed to the formation of new precipitates and increased hardness. Increasing the normal load resulted in a transition from mild to severe wear. In the mild wear regime, abrasion was the dominant wear mechanism, while in the severe wear regime, oxidative wear and delamination (a sign of spallation of oxidized patches) coexisted with abrasion were dominant mechanisms. Finally, finite element method was employed to model the wear behavior of studied alloys using ABAQUS software. A 3D model was developed to predict the wear depth evaluated from contact pressure, which was then used as an input into Archard's wear equation. In terms of wear rate, simulation results were in good agreement with experimental values, particularly in the mild wear regime.
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| 3. |
- Hemati, N., et al.
(författare)
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Effect of Rare Earth Elements on the Microstructural and Mechanical Properties of ZK60 Alloy after T5 Treatment
- 2022
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Ingår i: Russian Journal of Non-Ferrous Metals = Izvestiya VUZ. Tsvetnaya Metallurgiya. - : Springer Nature. - 1067-8212 .- 1934-970X. ; 63:2, s. 223-236
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the microstructure and mechanical properties of ZK60 extruded alloy were investigated after adding 3 wt % of Ce and Y and T5 operation. The microstructure of the base alloy consists of alpha-Mg and Mg7Zn3. In addition to these phases, MgZn2Ce and Mg3Y2Zn3 phases are formed by adding Ce and Y, respectively. The addition of rare earth elements reduces the grain size of the base alloy from 6.1 mu m to less than 3 mu m. The volume fraction of precipitates also increases because of the additions. After T5 operation for different times, it was observed that the hardness peak (88 HV) for the base alloy is achieved after 18 hours. However, the peak hardness of alloys containing rare earth elements occurred in 24 hours. Increasing the aging time results in an increase in the grain size of the base alloy, while it led to a slight increase in the grain size of alloys containing rare earth elements. The higher hardness at the peak age of all studied alloys is explained based on the increase in the volume fraction of precipitates during this operation. The delay in the peak age in alloys containing rare earth elements is due to the delay in the formation of beta(2’) precipitates. The shear punch test results of extruded alloys show that in alloys containing Ce and Y the shear strength is 156 and 160 MPa, respectively. While this value is about 148 MPa for the base alloy. At the peak age, this strength for ZK60-Ce and ZK60-Y alloys increases by 11% and 13%, respectively. Higher strength and hardness in Y-containing alloys are due to the simultaneous strengthening of solid solution and precipitates along with the formation of precipitates with high thermal stability.
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| 4. |
- Nafari, Afshin, et al.
(författare)
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Microstructural characterization, mechanical and tribological properties of ZC71 hybrid composite reinforced with SiC and MWCNT
- 2021
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Ingår i: Journal of Applied Research and Technology. - : Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico. - 1665-6423 .- 2448-6736. ; 19:4, s. 345-363
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, the influences of different SiC addition, MWCNTs and various SiC particle sizes on the structural, mechanical and tribological properties of ZC71 alloys were studied. The results revealed that the proper amount/size of SiC particles with the addition of MWCNTs had a considerable effect on the microstructural alteration, and mechanical and tribological properties of the ZC71 alloy. The Vickers hardness values of the ZC71 alloy improved with the addition of MWCNT and SiC. The UTS (216 MPa) and El.% (6.95 %) were achieved in the ZC71-5%SiC(15μm)-0.5%MWCNT. The cast ZC71 alloy showed brittle fracture with some quasi-cleavage characterizations. However, by adding 5% SiC (15 μm) and 0.5% MWCNT, the fracture mode changed to ductile fracture. The wear results showed that the ZC71-5%SiC-0.5%MWCNT hybrid composite had the highest wear resistance with the lowest friction coefficient and wear rate. Examination on the worn surface of the ZC71-5%SiC-0.5%MWCNT hybrid composite showed mild abrasion as the governing wear mechanism.
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| 5. |
- Najafi, Soroush, et al.
(författare)
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Processing Maps and Hot Compression Behaviors of ZK60 Alloy After Adding Different Rare Earth Elements
- 2023
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Ingår i: Journal of materials engineering and performance (Print). - : Springer Nature. - 1059-9495 .- 1544-1024. ; 32:5, s. 2249-2263
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the effect of adding 3 wt.% of light (Ce) and heavy (Y) rare earth elements on the microstructure and hot compression behavior of Mg-6 wt.% Zn-0.5 wt.% Zr (ZK60) extruded alloy was investigated. A compression test was performed on extruded alloys in the range of 0.001–1 s−1 strain rate and 250-400 °C temperature. By adding rare earth elements to the alloy, in addition to the Mg7Zn3 precipitates in ZK60 alloy, MgZn2Ce precipitates and Mg24Y5 and Mg3Y2Zn3 precipitates are formed in ZK60-3Ce and ZK60-3Y alloys, respectively. In addition to increasing the volume fraction of precipitates, rare earth elements also cause grain refinement. Hot working behavior was investigated using the modified hyperbolic sinus method. Stress exponent values between 5 and 7 and activation energy between 125 and 150 kJ mol−1 were obtained. Lattice self-diffusion for ZK60 alloys and cross-slip in alloys containing rare earth elements were suggested as deformation mechanisms. With the help of processing maps, suitable temperature and strain rate for hot working were obtained. It was found that with the addition of rare earth elements, the stable area becomes wide and the unstable areas become narrow.
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| 6. |
- Najafi, Soroush, et al.
(författare)
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The Effect of Y Addition on the Microstructure and Work Hardening Behavior of Mg-Zn-Zr Alloys
- 2021
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Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 30:4, s. 2574-2585
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Tidskriftsartikel (refereegranskat)abstract
- The effect of adding different amounts of Y on the microstructure, mechanical properties, texture and work hardening behavior of the extruded Mg-6Zn-0.5Zr-xY alloys (x = 0, 1, 2, 3 wt.%) was investigated. According to the results, the microstructure of all alloys is composed of α-Mg grains and Mg7Zn3 particles. By adding Y, in addition to grain refinement, Mg24Y5 and Mg3Y2Zn3 particles are formed in the microstructure. Among the alloys studied, the ZK60-3Y alloy has the highest strengths, as the yield stress and ultimate tensile strength of 318 and 366 MPa, respectively, were obtained for that alloy. This is due to the finer grains and higher volume fraction of the particles in the ZK60-3Y alloy. Meanwhile, reducing the grain size by Y addition affects the work hardening behavior; Y addition reduces the saturation stress, hardening capacity, and work hardening exponent by increasing the dynamic recovery; i.e., the more Y is added, the greater is the drop in the work hardening parameters. The effects of Y addition on work hardening behavior and dynamic recovery were investigated by examining microstructural developments, the volume fraction of particles and texture evaluation. The results of the texture evaluations showed that the addition of Y changes the texture component and intensity of the basal planes and can cause work hardening loss by activating slip on the non-basal planes.
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| 7. |
- Torkamani, Hadi, et al.
(författare)
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Effect of Rotation Speed and Steel Microstructure on Joint Formation in Friction Stir Spot Welding of Al Alloy to DP Steel
- 2022
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Ingår i: Journal of Manufacturing and Materials Processing. - : MDPI. - 2504-4494. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- In this work, friction stir spot welding of 5754 aluminum alloy to dual phase steel was investigated using two different ratios of martensite and ferrite (0.38 and 0.61) for steel sheet initial microstructure and varying tool rotation speed (800, 1200 and 2000 rpm). The effect of these parameters on the joint formation was evaluated by studying the plunging force response during the process and the main characteristics of the joint at (i) macrolevel, i.e., hook morphology and bond width, and (ii) microlevel, i.e., steel hook and sheet microstructure and intermetallic compounds. The plunging force was reduced by increased tool rotation speed while there was no significant effect from the initial steel microstructure ratio of martensite and ferrite on the plunging force. The macrostructural characterization of the joints showed that the hook morphology and bond width were affected by the steel sheet initial microstructures as well as by the tool rotation speed and by the material flow driver; tool pin or shoulder. At microstructural level, a progressive variation in the ratio of martensite and ferrite was observed for the steel hook and sheet microstructure. The zones closer to the tool presented a fully martensitic microstructure while the zones away from the tool showed a gradual increase in the ferrite amount until reaching the ratio of ferrite and martensite of the steel sheet initial microstructure. Different types of FexAly intermetallic compounds were found in three zones of the joint; the hook tips, in the hooks close to the exit hole and in the corner of the exit hole. These compounds were characterized by a brittle behavior with hardness values varying from 456 to 937 HV01.
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| 8. |
- Torkamani, Hadi, et al.
(författare)
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Low-carbon cast microalloyed steel intercritically heat-treated at different temperatures : microstructure and mechanical properties
- 2021
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Ingår i: Archives of Civil and Mechanical Engineering. - : Springer. - 1644-9665. ; 21:2
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Tidskriftsartikel (refereegranskat)abstract
- In this study, dual-phase (DP, ferrite + martensite) microstructures were obtained by performing intercritical heat treatments (IHT) at 750 and 800 °C followed by quenching. Decreasing the IHT temperature from 800 to 750 °C leads to: (i) a decrease in the volume fraction of austenite (martensite after quenching) from 0.68 to 0.36; (ii) ~ 100 °C decrease in martensite start temperature (Ms), mainly due to the higher carbon content of austenite and its smaller grains at 750 °C; (iii) a reduction in the block size of martensite from 1.9 to 1.2 μm as measured by EBSD. Having a higher carbon content and a finer block size, the localized microhardness of martensite islands increases from 380 HV (800 °C) to 504 HV (750 °C). Moreover, despite the different volume fractions of martensite obtained in DP microstructures, the hardness of the steels remained unchanged by changing the IHT temperature (~ 234 to 238 HV). Applying lower IHT temperature (lower fraction of martensite), the impact energy even decreased from 12 to 9 J due to the brittleness of the martensite phase. The results of the tensile tests indicate that by increasing the IHT temperature, the yield and ultimate tensile strengths of the DP steel increase from 493 to 770 MPa, and from 908 to 1080 MPa, respectively, while the total elongation decreases from 9.8 to 4.5%. In contrast to the normalized sample, formation of martensite in the DP steels could eliminate the yield point phenomenon in the tensile curves, as it generates free dislocations in adjacent ferrite.
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| 9. |
- Torkamani, Hadi, et al.
(författare)
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Micro-pitting and wear damage characterization of through hardened 100Cr6 and surface induction hardened C56E2 bearing steels
- 2022
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 492-493
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Tidskriftsartikel (refereegranskat)abstract
- Rolling-sliding contact fatigue experiments were performed on through hardened (TH) 100Cr6 and surface induction hardened (SIH) C56E2 bearing steels to study the effect of heat treatment procedure and hardness difference on their wear and/or surface-initiated damage. The heat-treated microstructures included tempered martensite without the presence of retained austenite. It was found that initial stress distribution below the surface of TH specimens remains close to zero with respect to the depth, while, employing SIH resulted in relatively high compressive residual stresses. The wear damage of the specimens was characterized for negative ΔH (i.e., specimen's hardness minus counterpart's hardness) subjected to rolling-sliding contact in a twin-disc configuration operated under a mixed lubrication condition. According to the wear mechanisms and damages assessed, three regions were distinguished: i) mild wear and onset of micropitting, ii) transition region from mild to severe micro-pitting and iii) severe micro-pitting wear. Decreasing the ΔH resulted in a gradual increase in the wear rate of TH specimens, while, the increase in the wear rate of SIH specimens was delayed; with a same absolute hardness, TH specimen with a ΔH of −84 HV already reached the third wear region, while a SIH specimen with a ΔH of −150 HV still operates in the second region. Inspection of the affected subsurface unveiled the response of worn microstructures to the etchant and how the micro-cracks could possibly form within the wear affected zone. The results obtained were mainly explained based on the state of the residual stresses, possible contributions of the microstructural features, and wear behavior (material removal) of the specimen.
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