Nanoscratching of metallic glasses – An atomistic study

Abstract

Tribological properties of materials play an important role in engineering applications. Up to now, a number of experimental studies have identified correlations between tribological parameters and the mechanical response. Using molecular dynamics simulations, we study abrasive wear behavior via nanoscratching of a Cu 64.5 Zr 35.5 metallic glass. The evolution of the normal and transverse forces and hardness values follows the behavior well known for crystalline substrates. In particular, the generation of the frontal pileup weakens the response of the material to the scratching tip and leads to a decrease of the transverse hardness as compared to the normal hardness. However, metallic glasses soften with increasing temperature, particularly above the glass transition temperature thus showing a higher tendency to structurally relax an applied stress. This plastic response is analyzed focusing on local regions of atoms which underwent strong von-Mises strains, since these are the basis of shear-transformation zones and shear bands. The volume occupied by these atoms increases with temperature, but large increases are only observed above the glass transition temperature. We quantify the generation of plasticity by the concept of plastic efficiency, which relates the generation of plastic volume inside the sample with the formation of external damage, viz. the scratch groove. In comparison to nanoindentation, the generation rate of the plastic volume during nanoscratching is significantly temperature dependent making the glass inside more damage-tolerant at lower temperature but more damage-susceptible at elevated temperatures.

A review of recent advances in tribology

“…A transient mixed lubrication-wear coupling model (MLW coupling model) is developed to investigate the mixed lubrication and wear performances of journal bearings [235]. Molecular dynamics simulation was used to study abrasive wear behavior via nanoscratching of a Cu64.5Zr35.5 metallic glass [236]. A new wear model for sub-rough surface contacts in the context of deformation and theories of adhesion was proposed [237].…”

Molecular dynamics simulation of grain size effect on friction and wear of nanocrystalline zirconium

“…Particularly, to compare the effects of various parameters on friction intuitively, we applied a constant load control instead of the usual used depth control on the tool, which requires more complex algorithms. 34 Therefore, the tool was continuously loaded throughout the sliding process, and the wear depth varied with the sliding distance. Finally, the sliding process was performed along the X direction for 150 Å at different velocities in 1,500,000 time steps.…”

Transition to chip serration in simulated cutting of metallic glasses

“…The severe shear rearrangement causes the disruption of the icosahedral network and leads to significant density changes [27,28]. Shear bands generated with various deformation mechanisms have been studied both experimentally [18,[21][22][23]29] and in simulations [30][31][32][33][34][35][36][37]. For the case of cutting simulations, the formation of a series of equidistant parallel shear bands in straight chips has been reported [6][7][8][9]; earlier cutting simulations [38][39][40] focused on the determination of cutting forces and did not report on the plasticity mechanisms.…”