Homogenization of Ingot Metallurgy Near-Gamma Titanium Aluminides

ABSTRACTThe elimination of microsegregation and subsequent breakdown of the lamellar structure in near-gamma titanium aluminides was investigated through a series of high temperature homogenization heat treatments and isothermal hot compression tests. The homogenization heat treatment studies revealed that microsegregation could be eliminated after approximately five hours or one and one-half hours at temperatures either 15 C or 40 C, respectively, above the transus in the single phase alpha field. Subsequent attempts to breakdown the coarse prior alpha grain, lamellar structure were successful at low strain rates (∼ 10−3 s−1) and temperatures low in the alpha + gamma phase field, but led to wedge cracking and gross fracture at high strain rates (∼ 1 s−1) high in the alpha + gamma phase field. Subsequent annealing treatments to globularize the hot-worked structure in order to obtain a uniform, fine, and stable grain structure were also identified.