Aluminum-Cu50Zr50 Metallic Glass Interface: Deformation Behavior, Deformation Mechanisms, Structure, And Fracture Studies

Abstract

The interface plays a vital role in determining the mechanical properties of the composites. For instance, the toughness of the composite decreases in the presence of a hard interface, and on the other hand, increases due to a soft interface. Hence, it is important to understand the characteristics of the interface. It has been reported that metallic glass particles (Fe-base, Al-base, Cu-base, and Zr-base) as reinforcement significantly improved the mechanical properties of Al alloy. It is because metallic glass (MG) reinforcement has better compatibility with the Al matrix and result in better interface bonding due to good wettability and metallic nature than conventional ceramic particles such as Al2O3 or SiC. However, there are seldom experimental or simulation studies carried out to understand the interface between metal-metallic glasses. Experimental studies of the interface are expensive and are also difficult due to sensitivity to many factors such as lattice mismatch, crystal defects, presence of impurities, thermal expansion coefficient mismatch and reactions at the interface. So, computer simulation technique such as molecular dynamics (MD) conducted at the atomic level is a good alternative for studying the interface properties which will help to address the effects observed at higher length scales.
Based on the above, MD simulations are carried out on Al (metal)-Cu50Zr50 (metallic glass) interface models to investigate the fracture strength (mode-I and mode-II), deformation behavior and mechanisms based on the cohesive zone model. Defects such as cracks and voids significantly alter the properties of the materials. So, an investigation on the effect of defects and the interaction between them is investigated in the interface model. The effect of sample size and cyclic loading on the deformation behavior and structural changes in Al and Cu50Zr50 MG is also investigated. The role of metallic glass thickness in the nano-layered structures is also identified. Nanoindentation studies can be used to estimate the mechanical properties of the matrix, interface and reinforcement in a confined region and the variation in the mechanical properties as a function of the separation distance between these. So, investigations are also performed on the spark plasma sintered Al-Cu50Zr50 bulk composites. MD simulations of nanoindentation are also carried out to gain insights into the bulk behavior and deformation mechanisms.
The MD simulation results suggest that during mode-I loading, fracture occurs in the Al region of the interface model and is attributed to the strong bonding between Al-Cu and Al-Zr atoms. The dominant deformation mechanism at the interface is by slip by Shockley partial dislocation motion. Amorphization of Al region and structural changes in Cu50Zr50 MG are observed during deformation. Tensile-compression loading, pre-strain effects reveal that SFT (stacking fault tetrahedral) is evolved in the Al region. Crack tip blunting occurs by dislocation emission at the crack tip, crack bowing out due to the presence of void is observed for all the sizes of voids. With an increase in the thickness of the MG layer, the strength of the nano-laminates has increased. From the load-indentation depth response, it is observed that there is variation in the mechanical properties such as elastic modulus and hardness as a function of the separation distance between matrix and reinforcement indicating the role of the interface. MD simulations of nanoindentation also show similar qualitative behavior.