The 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°C by heat-treating various ternary Re–Cr–Nb alloys in vacuum for either 2 or 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°C 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 the 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 limit of Re in the γ phase was 44–45 at% Re as the Cr content increased (i.e., Re content decreased) in the γ phase; the Cr content 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 limit of Nb in the σ phase tie-lined with the χ phase is 2 at% Nb.