Temperature-dependent vibrational properties of NiAl, CoAl, and FeAl β-phase alloys

Abstract

Temperature-dependent vibrational properties of β-phase NiAl, CoAl, and FeAl alloys have been studied by the extended x-ray-absorption-edge fine-structure (EXAFS) technique. From the $K$-edge EXAFS of the transition-metal element, the temperature dependence of the mean-squared relative displacements has been obtained, where these relative displacements are between the absorbing atom and the first, second, or third coordination shell. For NiAl, excellent agreement is obtained with calculations we have carried out, which are based on input from neutron-scattering data obtained by others. We find that the changes with temperature of the mean-squared relative displacements of corresponding atomic pairs are similar for NiAl and FeAl, but CoAl is significantly different from the other two alloys in this regard. In particular, the temperature dependence of the second- and third-neighbor Co-Co mean-squared relative displacement in CoAl is significantly less than the temperature dependence of the corresponding Ni-Ni and Fe-Fe mean-squared relative displacements in NiAl and FeAl, respectively.