D. Y. Seo, T. Sawatzky, H. Saari, D. J. Kim, P. Au, C. S. Seok
The Journal of Mechanical Science and Technology, vol. 26, no. 7, pp.2009-2013, 2012

Abstract : Pre-alloyed beta gamma titanium aluminide powder with a nominal composition of TiAl- 2Nb-2Mo (G2) is consolidated by hot isostatic pressing. After consolidation, a step cooled heat treatment is performed to homogenize the material and produce a fully lamellar microstructure. Various aging heat treatments are then performed to form interfacial beta phase precipitates along lamellar interfaces. The step cooled heat treatment produces a relatively fine microstructure with an average lamellar grain size of 40 μm. The aging heat treatments generate beta phase precipitates along lamellar grain boundaries as well as along lamellar interfaces, and result in limited lamellar degradation and grain growth. However, coarse intergranular grains consisting of beta and gamma grains form during aging. Constant load tensile creep tests are performed on step cooled heat treated and aged specimens. Primary creep resistance, generally, improves with aging time, even with interfacial precipitation, and the limited lamellar degradation occurs with aging. However, total creep life of aged samples decreases with aging time. The microstructures of the tested specimens are characterized and related to the creep behaviour of the TiAl-2Nb-2Mo alloy in the un-aged and aged conditions.

Keyword : Beta gamma TiAl alloy; Beta phase; Creep; Powder metallurgy