Investigation of the local structural rearrangement of Mg67Zn28Ca5 bulk metallic glasses during tensile deformation: A molecular dynamics study

Abstract

Mg67Zn28Ca5 bulk metallic glass (BMG) has been proven to have the highest corrosion resistance to a simulated body fluid solution amongst all MgZnCa BMGs (Zberg et al., 2009), and further studies on its mechanical properties and deformation mechanism under uniaxial tension have been conducted using molecular dynamics (MD) simulations. This study finds the predicted yielding stress and Young’s modulus derived from the stress–strain profile to be 702MPa and 51GPa, respectively, which are in good agreement with experimental results. The distribution of the atomic local shear strain was used to monitor the development of a shear transition zone (STZ) and the formation of a shear band during the tension. For the BMG system and the shear band region, the Honeycutt–Anderson (HA) pair analysis technique was adopted to analyze the local structural rearrangement in detail, and the free volume ratio was used to determine the extent of the increase in free volume. In the system, number 1551 and 1541 icosahedral local structures significantly decrease at strains from 0 to 0.05 and the initialization of STZs appears randomly throughout this strain range. When the strain increases further, the numbers of all HA indexes remain constant, and the extension of STZs evolves into two clear shear bands along a direction 45° from the tensile direction. In the shear band region, the fraction of Ca atom is about half the Ca fraction of Mg67Zn28Ca5 BMG, and the fraction of icosahedral local structures 1551, 1541, and 1431 are relatively higher than those distributed within the whole system. Also the value of the free volume ratio in the shear band region is much larger than that in the whole system. By investigating the variation of average atomic local strain values within the shear band, a four-stage deformation mechanism of local structure rearrangement is clearly indicated, consisting of elastic deformation, STZ initialization, STZ extension, and shear band formation.