Microstructural refinement and mechanical properties improvement of elemental powder metallurgy processed Ti-46.6Al-1.4Mn-2Mo alloy by carbon addition

Strengthening of a gamma TiAl alloy was sought by a chemical modification o f the composition with carbon. Up to 0.6 at. pet of carbon was added to the Ti-46.6Al-1.4Mn-2Mo alloy processed by elemental powder metallurgy. Carbon addition resulted in considerable microstructural changes such as refineme nt, by a factor of about. 2, of the lamellar microstructure and carbide pre cipitation. The cause of the lamellar structure refinement is twofold, incr eased heterogeneous nucleation rate and decreased gamma platelet growth rat e, the net result of which was a retarded diffusional transformation kineti cs of alpha to alpha/gamma lamellae. As a consequence of the microstructura l changes, the high-temperature tensile properties and the creep properties of the alloy were significantly improved. Anomalous hardening was also obs erved at 800 degreesC, resulting in a tensile yield strength of 700 MPa. Th e strengthening effect of carbon was realized by the microstructural refine ment and by precipitation hardening of intergranular as well as interlamell ar Ti3AlC. In terms of the tensile properties and the creep properties, the optimum amount of carbon addition was 0.3 at. pct.