Re-Cr-Ni 系における 1423 K の等温状態図の実験的決定

Abstract

Compositions with tie-lines between the γ, α, σ, and δ phases in a ternary Re-Cr-Ni system were investigated by heat-treating various ternary Re-Cr-Ni alloys in vacuum at 1423 K for a variety of heating times up to 2500 h. The microstructures of the Re-Cr-Ni alloys that had been water-quenched after heating were observed and their Re, Cr and Ni concentration profiles were measured using an electron probe micro-analyzer (EPMA). It was found that a very long heat treatment was required to obtain equilibrium compositions of Ar-arc-melted Re-Cr-Ni alloys. The tie-line compositions (at%) of each phase at 1423 K were experimentally determined, and an isothermal phase diagram was constructed. From these results, the γ, α, and σ phases of the three-phase coexistence state were found to have the following compositions: γ phase (3.0 at%Re, 45.6 at%Cr, and 51.4 at%Ni), α phase (16.1 at%Re, 75.2 at%Cr, and 8.7 at%Ni), and σ phase (16.3 at%Re, 60.3 at%Cr, and 23.4 at%Ni). In addition, the γ, σ, and δ phases have the following compositions: γ phase (13.3 at%Re, 18.1 at%Cr, and 68.6 at%Ni), σ phase (54.6 at%Re, 24.2 at%Cr, and 21.2 at%Ni), and δ phase (70.2 at%Re, 6.0 at%Cr, and 23.8 at%Ni). The solubility limits of Ni in the σ phase increased from 19 at%Ni to 24 at%Ni, as the Cr content in the σ phase with a tie-line with the γ phase increased from 23 at%Cr to 61 at%Cr.