Microstructural Refinement and Mechanical Properties Improvement of Elemental Powder Metallurgy Processed Ti-46.6Al-1.4Mn-2Mo Alloy by Carbon Addition

摘要

Strengthening of a gamma TiAl alloy was sought by a chemical modification of the composition with carbon. Up to 0.6 at. pct 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 refinement, by a factor of about 2, of the lamellar microstructure and carbide precipitation. The cause of the lamellar structure refinement is twofold, increased heterogeneous nucleation rate and decreased #gamma# platelet growth rate, the net result of which was a retarded diffusional transformation kinetics of #alpha# to #alpha#/#gamma# lamellae. As a consequence of the microstructural changes, the high-temperature tensile properties and the creep properties of the alloy were significantly improved. Anomalous hardening was also observed at 800 deg C, resulting in a tensile yield strength of 700 MPa. The strengthening effect of carbon was realized by the microstructural refinement and by precipitation hardening of intergranular as well as interlamellar Ti_3AlC. In terms of the tensile properties and the creep properties, the optimum amount of carbon addition was 0.3 at. pct.