Average ternary interdiffusion coefficients in Ni3Al with Ir additions have been
determined using solid-to-solid diffusion couples annealed at 1200°C for 5 hours. Disc shaped
alloy specimens were prepared by the vacuum arc melting at compositions of Ni-24Al, Ni-25Al,
Ni-26Al, Ni-23.5Al-1Ir, Ni-24.5Al-1Ir, Ni-23Al-2Ir, Ni-23Al-2Ir, Ni-24Al-2Ir, Ni-23Al-3Ir
(at.%). Surfaces of alloys were polished down to 1200 grit and diffusion couples were assembled
in Si3N4 jig for initial bonding heat treatment at 1200°C for 0.5 hours. Additional diffusion anneal
was carried out at 1200°C for 4.5 hours outside of Si3N4 jig so that diffusion couples can be water
quenched. Concentration profiles of individual components were measured by electron probe
microanalysis using pure standard of Ni, Al and Ir. Interdiffusion flux of individual component
was determined directly from the experimental concentration profiles, and the moments of
interdiffusion flux were examined to calculate the average ternary interdiffusion coefficients, D˜ ij
k
either with Al or Ni as dependent component. Calculated interdiffusion coefficients suggest that
Ir-alloyed Al2O3-forming oxidation resistant coatings would be beneficial to reduce the
interdiffusion flux of Ni from superalloy substrates to the coating, and reduce the interdiffusion
flux of Al from the coating to the superalloy substrate.