Experimental Determination of the Isothermal Section in a Ternary ReCrNb System at 1500°C+1

The compositions with tie-lines between the », ·, £, ¡, 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 220 h. 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 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 » phase tie-lined with the ¡ 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 ¡ 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 £ phase was 4445 at % 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 1.8 at % Cr to 9.8 at % Cr. The solubility limit of Nb in the · phase tie-lined with the » phase is 2 at % Nb. [doi:10.2320/matertrans.M2013282