Saeed Zare Chavoshi

Addressing the discrepancy of finding the equilibrium melting point of silicon using molecular dynamics simulations

We performed molecular dynamics simulations to study the equilibrium melting point of silicon using (i) the solid–liquid coexistence method and (ii) the Gibbs free energy technique, and compared our novel results with the previously published results obtained from the Monte Carlo (MC) void-nucleated melting method based on the Tersoff-ARK interatomic potential (Agrawal et al. Phys. Rev. B 72, 125206. (doi:10.1103/PhysRevB.72.125206)). Considerable discrepancy was observed (approx. 20%) between the former two methods and the MC void-nucleated melting result, leading us to question the applicability of the empirical MC void-nucleated melting method to study a wide range of atomic and molecular systems. A wider impact of the study is that it highlights the bottleneck of the Tersoff-ARK potential in correctly estimating the melting point of silicon.

Molecular dynamics simulation of the elliptical vibration assisted machining (EVAM) of pure iron

Abstract It is well known that diamond wears out rapidly (within several metres of cutting length) when machining low carbon ferrous alloys and pure iron. The past few years have seen a growing interest in the field of elliptical vibration-assisted machining (EVAM) due to it being successful in the micromachining of difficult-to-cut materials including steel. During EVAM, a cutting tool is prescribed an oscillatory motion perpendicular to the direction of cutting, thereby causing the tool to be relieved intermittently from chemical and physical contact with the workpiece. This phenomenon serves as a guideline to develop the simulation test bed for studying EVAM in this work to compare it with conventional cutting. The pilot implementation of the EVAM came as a quasi-3-dimensional (Q3D) elliptical cutting model of body-centred cubic (BCC) iron with a diamond cutting tool using molecular dynamics (MD) simulation. The developed MD model supplemented by the advanced visualization techniques was used to probe the material removal behaviour, the development of the peak stress in the workpiece and the way the cutting force evolves during the cutting process. One of the key observations was that the cutting chips of BCC iron during conventional cutting underwent crystal twinning and became polycrystalline, while EVAM resulted in cutting chips becoming highly disordered, leading to better viscous flow compared to conventional cutting.

A Review on Micro- and Nanoscratching/Tribology at High Temperatures: Instrumentation and Experimentation

High-temperature micro-/nanomechanics has attracted much interest over the last decade, primarily because of the urgent need to understand the mechanical and tribological properties of advanced engineering materials at micro-/nanoscale and the underlying physics controlling such properties at operationally relevant conditions. Recent years have subsequently witnessed the swift growth and development of new high-temperature micro- and nanoscratching/tribology instruments. Here, we present an overview of fundamental principles and developments in these instruments, discuss pertinent findings on the topic in detail, and outline current challenges and promising future directions in the field.

Tension-compression asymmetry in plasticity of nanotwinned 3C-SiC nanocrystals

Encompassing nanoscale thin twins in metals induces diverse influences, either strengthening triggered by the lattice dislocation blockage effects or softening prompted by dislocation emission from coherent twin boundary (CTB)/grain boundary (GB) intersections as well as CTB migration; yet the deformation mechanism remains poorly understood in ceramic nanostructures possessing covalent bonds. Here, we report the results of uniaxial compressive and tensile stress loading of twin-free and nanotwinned nanocrystalline cubic silicon carbide (3C-SiC) ceramic attained by large-scale molecular dynamics simulations. We find a strong and unique tension-compression asymmetry in strength of nanocrystalline ceramics, much higher than that of metals. We demystify that strength and ductility behaviour do not correlate simply with the amount of dislocation density, voids, intergranular disordered phase, and total strain energy; instead, it arises from a complex interplay of the aforementioned features and structural characteristics, e.g., GB and triple junction area distribution along/normal to the direction of straining as well as the capability of strain accommodation by the GBs and CTBs, with the dominant role of the structural characteristics in nanotwinned samples. Our results also reveal that primarily intergranular crack propagation and fracture along the GBs transpires, and not along the CTBs, resulting from the high energy of the GBs. However, a high density of nanoscale twins in the 3C-SiC nanocrystals could give rise to the alternation of the crack path from intergranular to intragranular type induced by shear, which brings about the glide of Shockley partials along the CTBs and subsequent formation of CTB steps and twin plane migration.Encompassing nanoscale thin twins in metals induces diverse influences, either strengthening triggered by the lattice dislocation blockage effects or softening prompted by dislocation emission from coherent twin boundary (CTB)/grain boundary (GB) intersections as well as CTB migration; yet the deformation mechanism remains poorly understood in ceramic nanostructures possessing covalent bonds. Here, we report the results of uniaxial compressive and tensile stress loading of twin-free and nanotwinned nanocrystalline cubic silicon carbide (3C-SiC) ceramic attained by large-scale molecular dynamics simulations. We find a strong and unique tension-compression asymmetry in strength of nanocrystalline ceramics, much higher than that of metals. We demystify that strength and ductility behaviour do not correlate simply with the amount of dislocation density, voids, intergranular disordered phase, and total strain energy; instead, it arises from a complex interplay of the aforementioned features and structural char...