Effects Of Composition And Multilayer Structure On The Mechanical Behaviors Of Some Amorphous Alloy Films

People concern about the strength of amorphous alloys, but also commit to improving their plasticity at room temperature. It has been found that the strength and plastic deformation behaviors of amorphous alloys are related with deformation rates, compositions and the addition of a second phase. The multilayer structure formed by inserting amorphous or crystalline layer into amorphous films may affect the strength and plastic deformation, which is worthy of an in-depth study. In this dissertation, amorphous CuW films and CoZrNb/S(S=Ag, Cu, CuTa) multilayers were prepared by magnetron sputtering. Their structure was characterized with various methods, and their mechanical properties including hardness, elastic modulus and plastic deformation behavior were tested by nanoindentation technique. After studying the mechanical behaviors of amorphous alloy films, we analyzed the relationship between hardness and periodical structure, and explored the characterizations, characteristics and mechanisms of plastic deformation of amorphous-based multilayers.The results show that both amorphous alloy films and amorphous-based multilayers deform by localized shear bands. The deformation characteristics vary with strain rate, composition and multilayer structure. For amorphous CuW films, lower strain rate and lower Cu content promote more obvious serrated flow on load-displacement curves. With the increase of strain rate and Cu content, the serrated flow characteristics weaken. The increasing strain rate and Cu content also result in increasing number of shear bands around nanoindents, and then increasing the plasticity. For amorphous CoZrNb films, the inserting crystalline layers, forming amorphous/crystalline multilayer structure, could both inhibit the propagation of shear bands and promote the nucleation of shear bands, which increases the plasticity. What's more, the effect is more pronounced when the periodicity is smaller. Nanoscratch results show that there exists a critical load, above which the samples fracture along the scratch tracks. The critical load can be used to characterize quantitatively the plasticity of CoZrNb and CoZrNb/Cu films. For amorphous CoZrNb film, the critical load is only 46mN. For the multilayer withΛ=8nm, the critical load is larger than 100mN. The addition of CuTa amorphous layers into the CoZrNb amorphous alloy has little effect on the plastic deformation.For amorphous/crystalline multilayers, there exists hardness enhancement with the decrease of the periodicity. The extent of hardness enhancement is closely related to the strength mismatch of component elements. With the decrease of the strength mismatch, the hardness enhancement increases. The strength mismatch theory, which is originally put forward to the crystalline/crystalline multilayers, is also suited to amorphous/crystalline multilayers. CoZrNb/Ag system with the largest strength mismatch shows a softening effect, whenΛ≥16nm, which can be ascribed to the localization of plastic deformation in softer Ag layers.For CoZrNb/CuTa multilayers, there is no hardness enhancement with decreasing periodicity, which can be attributed to the absence of the dislocation movement. After thermal annealing, the density increases due to the decrease of the bond distance (the Co-Co average bond distance decreases from 0.2496nm to 0.2397nm) and the annihilation of defects with increasing annealing temperature. The densification results in the enhancement of both elastic modulus and hardness.