Compositions with tie lines between the σ and (γ,δ) phases in a ternary Re-Cr-Ni system were investigated by heat treating various ternary Re-Cr-Ni alloys at 1573 K in vacuum for up to 2000 h. The microstructures of the Re-containing alloys that had been water quenched after various heat treatment for times were observed and their concentration profiles for Re, Cr, and Ni were measured using an electron probe microanalyzer. The Re-Cr-Ni alloys consisted of the σ phase with either the γ or δ phase. The concentration profiles of the γ phase became flat after short heat treatment, whereas longer times of up to 2000 h were required to achieve the same effect for the σ and δ phases.
The tie-line composition (at%) of each phase at 1573 K was experimentally determined as follows. The σ phase tie-line with the γ phase (17.3 Re, 20.6 Cr, and 62.1 Ni) consists of 53.1 Re, 25.5 Cr, and 21.4 Ni. The σ phase tie-lined with the γ phase (16.9 Re, 19.2 Cr, and 63.9 Ni) consists of 53.0 Re, 24.6 Cr, and 22.4 Ni. The σ phase tie-line with the γ phase (12.7 Re, 24.8 Cr, and 62.5 Ni) consists of 48.4 Re, 30.9 Cr, and 20.7 Ni. The σ phase tie-line with the γ phase (6.1 Re, 46.2 Cr, and 47.7 Ni) consists of 28.1 Re, 52.3 Cr, and 19.6 Ni. The σ phase tie-line with the δ phase (85.6 Re, 5.2 Cr, and 9.2 Ni) consists of 61.1 Re, 27.7 Cr, and 11.2 Ni.