The phase equilibria of N₃Al evaluated by directional solidification and diffusion couple experiments

Abstract

Three solid phases are involved in the phase equilibria of the important intermetallic compound N1₃Al near its melting point, β, γ′(Ni₃AI) and γ. The generally-accepted phase diagram involves a eutectic reaction between γ′ and γ, but some recent studies agree with an older diagram due to Schramm, 5 which has a eutectic reaction between the β and γ′ phases. This work uses diffusion couple experiments to evaluate the equilibria at temperatures just below the liquidus, and it examines the liquidus region using quenched, directional solidification experiments that preserve the microstructures formed at the solidification front. At the growth rate studied, 61 μm/s, the eutectic forms between the γ and γ′ phases, as in the Schramm diagram.