Compositions with tie-lines between the σ, γ, and δ phases in a ternary Re-Cr-Ni system were investigated at 1423 K by heat-treating various ternary Re-Cr-Ni alloys and a binary Re-40 at%Ni alloy in vacuum for times up to 8640 ks. The microstructures of the Re-containing alloys which had been water-quenched after various heating times were observed and their concentration profiles for Re, Cr and Ni were measured using an electron probe micro-analyzer. The Re-Cr-Ni alloys consisted of the γ phase with either the σ or δ phase. It was found that concentration profiles of the γ phase became flat after short heat treatment, but longer times of up to 8640 ks were required to achieve the same effect for the σ and δ phases.
As the Cr contents increased (i.e., Re contents decreased) in the γ phase, the solubility limits of Ni in the σ phase tie-lined with the γ phase increased from 19 at%Ni to 24 at%Ni. The δ phase tie-lined with the γ phase(11.8 at%Re, 11.5 at%Cr, and 76.7 at%Ni) has 71.1 at%Re, 3.2 at%Cr, and 25.7 at%Ni. The Ni contents in the δ phase in a binary Re-Ni system are 30 and 35 at%Ni at 1573 and 1773 K, respectively. It was concluded that compositions of the γ phase tie-lined with the σ and δ phases coincided with those in the calculated and experimentally determined phase diagrams, respectively.
