Ab initio calculations on elastic properties in L12 structure Al3X and X3Al-type (X=transition or main group metal) intermetallic compounds

As high-temperature structural materials, L12 intermetallic compounds have attracted the strong interest from both fundamental and industrial aspects. Understanding of elastic property is a basis for the complete investigations of mechanical behavior of L12 alloys. In an effort to explore the electronic origin of elastic properties of L12 intermetallics, we have performed a systematic study on elastic constants for single crystals, and Youngʹs modulus, shear modulus, bulk modulus and Poissonʹs ratio for poly-crystals of 22 known Al3X and X3Al-type (X=transition or main group metal) intermetallics using the ab initio calculations. Based on the calculations of elastic constants and extreme (both positive and negative) Poissonʹs ratios, we found a pronounced correlation between the extreme Poissonʹs ratio and the elastic anisotropy, i.e., approximate 40% of the investigated L12 intermetallics exhibit intrinsic auxetic behavior. Furthermore, based on the distribution of bonding charge densities, we revealed that the ductility and extreme Poissonʹs ratios were attributable to the directionality of bonds of these alloys. Our findings provide a new method to predict mechanical behavior of intermetallics.