The pressure dependence of point-defect concentrations was calculated on the basis of 2 recently published models. It was demonstrated that the effective formation volume of vacancies exhibited an asymmetrical character about stoichiometry. For Ni-rich and stoichiometric compositions, the concentration of Ni vacancies versus pressure could be

described by a simple exponential function. The concentration of Ni antisite defects was independent of pressure. For Al-rich compositions, the concentration of Ni vacancies exhibited a more complex behaviour. At low pressures, the vacancy concentration was independent of pressure and the effective formation volume was zero while, above a critical pressure, the vacancy concentration became pressure-dependent. This could be explained by the annihilation reaction of Ni vacancies. The pressure of complete replacement depended upon the stoichiometry and proved to be very sensitive to the input parameters used in the various models. The changes expected in diffusion activation energy and activation volume with composition were considered on the basis of calculated temperature and pressure dependences of Ni vacancy concentrations; assuming vacancy-mediated diffusion. The pressure effect upon the boundary that separated regions within which triple defects or inter-branch defects predominated was also investigated. It was observed that pressure expanded the region in which Al inter-branch defects predominated.

Point-Defect Concentrations in B2 NiAl Alloys under Pressure. G.Erdélyi, C.Guthy, D.L.Beke: Philosophical Magazine, 2003, 83[1], 109-23