Tribological Behavior And Wear Mechanism Of Zr-based Bulk Metallic Glasses

Wear resistance is an important indicator of material performances in engineering applications.In this paper,in order to promote the application of bulk metallic glasses?BMGs?as structural materials,the effects of the alloy composition,structure,and geometry of counterparts on the friction and wear behavior of Zr-based BMGs were systematically studied.The wear mechanism of Zr-based BMGs was also discussed.Firstly,the effects of alloy composition on the dry friction and wear behavior as well as wear mechanism of Zr₅₅Al₁₀Ni₅Cu₃₀,Zr₅₃Al₁₆Co_23.25Ag_7.75,Zr₅₃Al₁₆Co₃₁ and Zr₅₃Al₁₆Co₂₆Pt₅ BMGs were investigated.The specific wear rates of those Zr-based BMGs are between 14.25-18×10^-8 mm³·mm^-1·N^-1,and the friction coefficient is around 0.6-0.7.It is found that the wear mechanism of all Zr-based BMGs is abrasive-and oxidation-wear.The Zr-based BMGs with different alloy compositions have different hardness and Poisson's ratio.The wear resistance of Zr-based BMGs is affected by the synergistic effect of hardness and toughness.Besides,it is seen that the wear resistance of BMGs is related to the hardness and Poisson's ratio.The wear resistance of BMGs is enhanced with the increase in the hardness and Poisson's ratio.Secondly,the effect of the geometry of counterparts on the micro-scratch behavior and mechanism of Zr₅₅Al₁₀Ni₅Cu₃₀ BMG was studied.As the geometry of counterparts decreases from the order of millimeter to micronmeter,the wear mechanism of the Zr₅₅Al₁₀Ni₅Cu₃₀ BMG under micro-scratch conditions is abrasive wear,without the presence of oxidation.The stress distribution simulation results of Zr₅₅Al₁₀Ni₅Cu₃₀ BMG show that the stress concentration of the Zr-based BMG under low stress condition is mainly distributed on the surface of the sample,and the scratch damage of the Zr-based BMG is mainly controlled by plastic deformation.Under high stress condition,the stress concentration is mainly distributed in the subsurface region with a certain depth from the surface of the specimen,and the scratching of the Zr-based BMG is dominantly driven by the nucleation and propagation of shear bands and microcracks.Finally,the Zr₅₅Al₁₀Ni₅Cu₃₀ BMG with different relaxation and crystallization conditions were obtained by vacuum heat treatment.The dry friction and wear behavior and mechanism of the Zr₅₅Al₁₀Ni₅Cu₃₀ BMG were studied.The experimental results show that the specific wear rate of the Zr₅₅Al₁₀Ni₅Cu₃₀ BMG decreases with the increase in annealing temperature,and the wear mechanism of the Zr₅₅Al₁₀Ni₅Cu₃₀ BMG is controlled by abrasive wear and oxidation wear.The oxidation resistance of the Zr₅₅Al₁₀Ni₅Cu₃₀ BMG under sliding is reduced by the vacuum annealing treatment.The oxidation of the Zr₅₅Al₁₀Ni₅Cu₃₀ BMG during the sliding process is faciliated with the increase in the temperature of annealing.The hardness of the Zr₅₅Al₁₀Ni₅Cu₃₀ BMG increases with the increasing annealing temperature.When crystallization of the Zr₅₅Al₁₀Ni₅Cu₃₀ BMG occurs,the hardness increases remarkably.This may be related to the formation of oxidation products with high hardness on the surface of the wear scar.In summary,the specific wear rate of Zr-based BMGs is mainly controlled by the synergistic effect of hardness and toughness.The wear failure mode is highly dependent on to the stress distribution state of the wear surface.The wear resistance of the Zr-based BMGs can be enhanced by structurally relaxed and crystallization.The results of this study are of great significance to promote the application of Zr-based BMGs.