Experimental Determination of the Isothermal Section in a Ternary Re–Cr–Nb System at 1500°C

Abstract

The compositions with tie-lines between the », ·, £, i, and Nb(Cr,Re)2 phases in a ternary Re­Cr­Nb system were investigated at 1500°C by heat-treating various ternary Re­Cr­Nb alloys in vacuum for either 2 or 220h. The microstructures of the Re­Cr­Nb alloys that had been water-quenched after heating were observed and their Re, Cr, and Nb concentration profiles were measured using an electron probe microanalyzer (EPMA). The tie-line compositions (at%) of each phase at 1500°C were experimentally determined, and an isothermal phase diagram was constructed. The » phase tie-lined with the i phase (26.4at% Re, 70.0at% Cr, and 3.6at% Nb) consists of 42.7at% Re, 40.8at% Cr, and 16.5at% Nb. The i phase tie-lined with the Nb(Cr,Re)2 phase (28.1at% Re, 41.9at% Cr, and 30.0at% Nb) consists of 24.6at% Re, 71.2at% Cr, and 4.2at% Nb. The solubility limit of Re in the £ phase was 44­45at% Re as the Cr content increased (i.e., Re content decreased) in the £ phase; the Cr content in the » phase with a tie-line with the £ phase increased from 1.8at% Cr to 9.8at% Cr. The solubility limit of Nb in the · phase tie-lined with the » phase is 2at% Nb. [doi:10.2320/matertrans.M2013282]