Tie-Lined Compositions of the σ and (γ, γ′, β) Phases in a Ni-Al-Re-Cr System at 1423 K

Compositions with tie-lines between the sigma and (gamma, gamma', beta) phases in a quaternary Ni-Al-Re-Cr system were investigated by heat-treating various quaternary Ni-Al-Re-Cr alloys in vacuum at 1423 K for a variety of heating times up to 2750 h. The microstructures of the Ni-Al-Re-Cr alloys that had been water-quenched after heating were observed and their Ni, Al, Re, and Cr 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 Ni-Al-Re-Cr alloys. The tie-lined compositions (at%) of each phase at 1423 K were experimentally determined as follows. The sigma phase tie-lined with the gamma phase (73.5Ni, 14.6Al, 2.9Re, and 9.0Cr) consists of 56.7Re, 25.0Cr, 18.1Ni, and 0.2Al. The sigma phase tie-lined with the gamma phase (70.5Ni, 14.3Al, 2.0Re, and 13.2Cr) has 47.7Re, 36.2Cr, 15.9Ni, and 0.2Al. The sigma phase tie-lined with the gamma' phase (73.6Ni, 21.0Al, 1.2Re, and 4.2Cr) consists of 58.3Re, 25.0Cr, 16.6Ni, and 0.1Al. The sigma phase tie-lined with the beta phase (50.2Ni, 48.7Al, 0.3Re, and 0.8Cr) consists of 61.1Re, 32.5Cr, 5.2Ni, and 1.2Al. The sigma phase tie-lined with the beta phase (65.1Ni, 29.5Al, 0.4Re, and 5.0Cr) consists of 45.8Re, 39.3Cr, 14.6Ni, and 0.3Al.