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- AlMotasem, Ahmed Tamer, et al.
(författare)
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Adhesion between ferrite iron-€“iron/cementite countersurfaces : A molecular dynamics study
- 2016
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Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 103, s. 113-120
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Tidskriftsartikel (refereegranskat)abstract
- The adhesive properties of Fe(110)/Fe(110) and Fe3C(001)/Fe(110) countersurfaces have been investigated by using classical molecular dynamics simulations. The simulation results show that Fe3C/Fe exhibits a relatively lower adhesion compared to the Fe/Fe. Additionally, the temperature dependence of the adhesive properties between 300–700 K has been examined. The results demonstrate that, with increasing the temperature, the values of the adhesion force and the work of adhesion continuously decrease in the case of Fe3C/Fe; they initially slightly increase up to 500 K then decrease in the case of Fe/Fe. Furthermore, the effect of lattice coherency between Fe/Fe has been examined and found to slightly reduce the adhesion. These results explain how carbides improve galling resistance of tool steel observed during dry sliding.
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| 3. |
- AlMotasem, Ahmed Tamer, et al.
(författare)
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Atomistic insights on the wear/friction behavior of nanocrystalline ferrite during nanoscratching as revealed by molecular dynamics
- 2017
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Ingår i: Tribology letters. - New York : Springer. - 1023-8883 .- 1573-2711. ; 65:3, s. 101-
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Tidskriftsartikel (refereegranskat)abstract
- Using embedded atom method potential, extensive large-scale molecular dynamics (MD) simulations of nanoindentation/nanoscratching of nanocrystalline (nc) iron have been carried out to explore grain size dependence of wear response. MD results show no clear dependence of the frictional and normal forces on the grain size, and the single-crystal (sc) iron has higher frictional and normal force compared to nc-samples. For all samples, the dislocation- mediated mechanism is the primary cause of plastic deformation in both nanoindentation/nanoscratch. However, secondary cooperative mechanisms are varied significantly according to grain size. Pileup formation was observed in the front of and sideways of the tool, and they exhibit strong dependence on grain orientation rather than grain size. Tip size has significant impact on nanoscratch characteristics; both frictional and normal forces monotonically increase as tip radii increase, while the friction coefficient value drops by about 38%. Additionally, the increase in scratch depth leads to an increase in frictional and normal forces as well as friction coefficient. To elucidate the relevance of indentation/scratch results with mechanical properties, uniaxial tensile test was performed for nc-samples, and the result indicates the existence of both the regular and inverse Hall-Petch relations at critical grain size of 110.9 angstrom. The present results suggest that indentation/scratch hardness has no apparent correlation with the mechanical properties of the substrate, whereas the plastic deformation has.
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| 4. |
- AlMotasem, Ahmed Tamer, et al.
(författare)
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Nanoindentation and nanoscratching of a ferrite/austenite iron bi-crystal : An atomistic study
- 2018
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Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 127, s. 231-239
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations are applied to investigate the wear/friction behavior of a ferrite/austenite iron bi-crystal, as a model system for duplex stainless steels. The plasticity of the ferrite phase is dominated by dislocations while both dislocations and stacking faults are the primary cause of plastic deformation of the austenite phase. Interestingly, the responses of tribological parameters vary depending on the scratch direction. For instance, the scratch hardness is increased by about 46% whereas the friction coefficient is reduced by about 22% when scratch starts from austenite to ferrite. At the interface, a local softening/hardening occurs because of dislocation-interface interaction. The present results demonstrate that martensitic phase transformation is responsible for experimentally observed high amount of ferrite of the pile-up.
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| 5. |
- AlMotasem, Ahmed Tamer, et al.
(författare)
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Tool microstructure impact on the wear behavior of ferrite iron during nanoscratching : An atomic level simulation
- 2017
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 370-371, s. 39-45
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, molecular dynamics simulations were used to investigate the impact of the tool microstructure on the wear behavior of ferrite workpiece during nanoscratching. The tool microstructure was modified by varying the carbide (cementite) contents. The simulation results show that dislocations are the primary mechanism for plastic deformation of the workpiece material. It is found that total dislocation length varies significantly depending on the carbide content in the tool. Furthermore, other tribological phenomena were also observed to depend on the carbide contents. For example, the average value of frictional forces decreased while the normal force increases with increasing carbide contents, and hence the friction coefficient was decreased. Additionally, the shape and size of lateral and frontal pileups are lowered. The structural analysis of the pileup region reveals the loss of long range order and start of amorphisation. The temperature distribution of the pileup regions showed an increase of the pileup temperature when carbide is added into tool. The wear volume is considerably reduced when the carbide content increases. The average scratch hardness was found to decrease and the result was analyzed with the theoretical Taylor hardening model.
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| 10. |
- Bergström, Jens, et al.
(författare)
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Fatigue of cold work tool steel
- 1999
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Ingår i: Matériaux & Techniques. - : EDP Sciences. - 0032-6895 .- 1778-3771. ; 87:1-2, s. 9-14
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Tidskriftsartikel (refereegranskat)abstract
- One important surface property of forming tools is their resistance to cracking due to fatigue loading. The wide variety of steel grades, material handling, machining operations and surface treatments will give very different fatigue properties. The present article gives examples on the influence of steel grades, EDM machining and surface coating. Initial cracks may be introduced in the tool during the processing to its final shape and surface finish, why a particular interest is given to small cracks introduced by the EDM process.
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