A model analysis of the elastic constants of metals and alloy phases

A lattice energy function using a Mie inverse power interatomic potential and a quadrupole distortion term was fitted to the cohesive energy, lattice parameter, bulk modulus and C₄₄ of pure metals. Using this function and the fitted parameters, values were then predicted for C₄₄ and other elastic constants of alloy phases. It was found that the maximum discrepancy in C₄₄ for B2, C15, and L1₂ type phases was 40%, with the RMS value equal to 25%.It was found that the predicted nearest-neighbor bond angle dependent elastic constants were always smaller than the observed values. It is believed that this result is due to the formation of eovalent bonds in the alloy phases, a phenomenon that is not included in the model. An empirical procedure for correcting the elastic constants to account for eovalent bonding reduces the maximum discrepancy in both shear constants to less than 20%. Evidence is presented in support of this hypothesis. One of the consequences of this work is that ground state superstructures, of heteroelectronic type alloy components that are deduced on the basis of constancy of pair or many body interactions, need not necessarily correspond to the most stable superstructures.