Alloy design of gamma titanium aluminides based on phrase diagrams

Phase stability in the Ti-Al-X (X = Cr, Mo and W) system has been investigated at 1473 and 1573 K by the following methods: microstructure observation of quenched specimens, diffusion coupling experiments, thermal analysis of DTA and in situ observation of X-ray diffraction. The ternary phase diagrams of Ti-Al-X system are proposed; additions of Cr, Mo and W stabilize the beta phase in the ternary phase diagrams. The tendency of 'beta stabilizer' is in the following order: 6 at% Cr = 3 at% Mo = 1 at% W is approximately equal to 10 vol% beta phase. In these TI-Al-X ternary systems, the alpha + beta + gamma three-phase coexisting region is close to the Ti-Al binary line and sifts slightly toward a higher concentration of Al as temperature increases. Based on the ternary phase diagrams, (gamma + beta) TiAl having a super-plastic capability and partial lamellar (P-L) microstructure which shows relatively well balanced mechanical properties from room temperature to elevated temperatures have been rationalized. (C) 1998 Elsevier Science Limited. All rights reserved.