Deformation mechanisms and mechanical properties of nanocrystalline CuxNi100−x alloys during indentation using molecular dynamics

Abstract

The mechanical property of polycrystal CuNi alloys under the indentation process is studied using molecular dynamics (MD) simulation. The effects of the grain size, temperature, and alloy component on hardness, and reduced elastic modulus are analyzed. We survey hardness with many different grain sizes to understand the inverse Hall-Petch and Hall-Petch relations of polycrystal CuNi. With a smaller grain size below the breakdown point (11.5 nm), the reverse Hall-Petch relationship is discovered; the rotation of grain and the grain boundary sliding are the dominant deformations of the workpieces during the indentation process. Meanwhile, a Hall-Petch relationship is observed when the particle size is larger than 11.5 nm. The structural evolution of nanocrystalline CuNi reveals that dislocation propagation dominates in the Hall-Petch regime. It is emphasised that the grain boundary plays an important key in the distribution of stress and spread of strain during the deformation. The result shows that high stress, strain, and dislocation not only concenter under the indenter but also in the grain boundary. The hardness, force, and reduced elastic modulus rise as the Ni component increases when we investigate the influence of different components on the deformation property. Moreover, the impact of temperatures on the mechanical properties of the sample is also investigated. Decreasing the temperature results in rising in the hardness, indenting force, and reduced elastic modulus. The total dislocation length at a temperature of 700 K is much smaller than other temperatures due to the amorphization.