Formation of microstructures in the molybdenum-aluminum-titanium ternary system through eutectoid decomposition

Formation and evolution processes of microstructure of Mo-Al alloys retarded by addition of 10 at% Ti are studied through various heat treatments. Fine acicular Mo₃Al precipitates are observed inside a grain for a specimen quenched at 1673 K as an initial stage of the eutectoid decomposition of bcc phase. It suggests that there is a crystallographic orientation relationship between the bcc matrix and A15 precipitates. By changing heat treatment conditions, fraction of fine lamellar structure decreases and spheroidized area increases. Subsequent aging treatment at lower temperature also provides the spheroidized structure. A coarse equiaxed structure is observed for a specimen quenched at 1673 K then aged at 1173 K.