Al Composition Dependence of Pt, Mn and V Diffusion in Ll2 - Type Ordered Ni3Al

The Al composition dependence of diffusion coefficients of Pt (substituting for Ni atoms on face centered sites in the Ni 3 Al, referred to as α-sites), Mn (for Al atom on corner sites, β-sites) and V (for both the atoms) atoms in the Ni 3 Al phase was studied by using the diffusion couple method. The diffusion coefficients of Pt, Mn and V elements increase with increasing Al composition of Ni 3 Al. These composition dependences are consistent with that of vacancy concentrations at α-sites in Ni 3 Al calculated by Kim. The activation energy of V diffusion is by about 110 kJ/mol higher than those of Pt and Mn. This high activation energy includes the increase in the total bond energy due to the jump of V atom from β- to α-sites. The above results verified that the V atom jumps to an adjacent vacant α-site and then it diffuses randomly through α-sites until it jumps to a vacant β-site.