Compositions with tie-lines between the χ, σ, γ, α, and Nb(Cr, Re)2 phases in a ternary Re-Cr-Nb system were investigated at 1500℃ by heat-treating various ternary Re-Cr-Nb alloys in vacuum for 2 h and 220 h. The microstructures of the Re-Cr-Nb alloys that had been water-quenched after heating were observed and their Re, Cr and Nb concentration profiles were measured using an electron probe micro-analyzer (EPMA).
The tie-line compositions (at%) of each phase at 1500℃ were experimentally determined, and an isothermal phase diagram was constructed. The χ phase tie-lined with the α phase (26.4 at%Re, 70.0 at%Cr, and 3.6 at%Nb) consists of 42.7 at%Re, 40.8 at%Cr, and 16.5 at%Nb. The α phase tie-lined with Nb(Cr, Re)2 phase (28.1 at%Re, 41.9 at%Cr, and 30.0 at%Nb) consists of 24.6 at%Re, 71.2 at%Cr, and 4.2 at%Nb. The solubility limits of Re in the γ phase has 44-45 at%Re, as the Cr contents increased (i.e., Re contents decreased) in the γ phase, the Cr contents in the χ phase with a tie-line with the γ phase increased from 1.8 at%Cr to 9.8 at%Cr. The solubility limits of Nb in the σ phase tie-lined with the χ phase are 2 at%Nb.
