Lattice parameters and bonding characteristics of hafnium containing trinickel aluminide alloys

The lattice parameters of the γ′ phase (Ni3Al) in a number of alloys containing hafnium were measured at room temperature after quenching from the equilibration temperature of 1130 °C. The lattice parameter a in angstroms could be expressed by the following best fit expression: a = 4.839725 − 2.492 X Ni − 1.295 X Al + 1.54 X Ni 2 + 3.89 X Al 2 − 0.98 X Ni X Al where XNi and XAl are the atom fraction of nickel and aluminium in the alloy respectively. The partial volumes of the components calculated from the above data shows that the partial volume of aluminium changes significantly with changes in the composition compared with the partial volumes of nickel and hafnium. The results indicate that hafnium has considerable covalent character and the covalent characteristics of aluminium have the tendency to increase appreciably with increase in hafnium content. The lattice parameters of the binary stoichiometric γ′ phase measured as a function of quenching temperatures show unusual temperature dependence. This has been attributed to the changes in the defect concentration of Ni3Al.