Elastic constants of face-centered cubic and L1 2 Ni-Si alloys: Composition and temperature dependence

The adiabatic elastic stiffness constants C ij of Ni-Si single-crystal solid-solution alloys of two slightly different compositions, 10.78 and 11.17 at. pct Si, were measured over the temperature range from 20 °C to 900 °C using the rectangular parallelepiped resonance method. The isotropic elastic constants of the polycrystalline ordered intermetallic compound Ni 3 Si containing 23 at. pct Si were also measured over this temperature range. Values of the C ij for Ni 3 Si were estimated from the data on the polycrystalline alloy, as well as from published data in the literature on isomorphous ternary ordered intermetallic compounds containing different amounts of Si. Using measured values and previously published data, the stiffness constants of Ni 3 Ti were estimated; these are the only available data on this alloy. The estimated single-crystal elastic constants of Ni 3 Si, as well as the experimentally measured bulk modulus, are considerably smaller than published values calculated from first-principles methods. The same is true for the C ij of Ni 3 Ti, but the discrepancies are smaller.