Effects of Ir or Ta Alloying Addition on Interdiffusion of L1₂-Ni₃Al

Ternary interdiffusion in L1₂-Ni₃Al with ternary alloying additions of Ir and Ta was investigated at 1473 K using solid-to-solid diffusion couples. Average ternary interdiffusion coefficients were determined from an integration of interdiffusion fluxes calculated directly from experimental concentration profiles. The magnitude of over(over(D, ̃), -)_NiNi and over(over(D, ̃), -)_AlAl coefficients was determined to be much larger than that of over(over(D, ̃), -)_IrIr and over(over(D, ̃), -)_TaTa coefficients. Ir substituting in Ni-site influenced the interdiffusion of Ni significantly, and over(over(D, ̃), -)_NiIr^Al coefficients were determined to be large and positive. On the other hand, Ta substituting for Al influenced the interdiffusion of Al significantly, and over(over(D, ̃), -)_AlTa^Ni coefficients were determined to be large and positive. An excellent agreement was found with ternary interdiffusion coefficients determined by Boltzmann-Matano analysis. Profiles of concentrations and interdiffusion fluxes were also examined to estimate binary interdiffusion coefficients in Ni₃Al, and tracer diffusion coefficients of Ir (14.7 × 10^-16 ± 1.4 × 10^-16 m²/s) and Ta (2.6 × 10^-16 ± 2.4 × 10^-16 m²/s) in Ni₃Al.