Orthorhombic titanium aluminides: Phases, phase transformations and microstructure evolution

The development of light weight high temperature materials with high streng th and high creep resistance is strongly driven by turbine engine manufactu rers. Titanium aluminides represent an important class of alloys, which pro vide a unique set of physical and mechanical properties that can lead to su bstantial payoffs in future aircraft engines. The class of orthorhombic tit anium aluminides based on the intermetallic phase Ti2AlNb represents the yo ungest material emerging out of the group of titanium aluminides. The monol ithic Ti2AlNb base material exhibits an attractive combination of low tempe rature ductility and high temperature tensile strength and creep resistance . The mechanical property profile and the high chemical compatibility of or thorhombic alloys with SiC fibers in titanium matrix composites make them a lso very attractive for high temperature use. In this paper the phases, pha se transformations, and microstructure evolution by thermomechanical proces sing of orthorhombic alloys is described based on investigations of the Ti2 AlNb base alloy Ti-22Al25Nb (at.%). Thermomechanical processing was success ful in producing equiaxed as well as defined coarse and fine grained lamell ar microstructures. Depending on heat treatment two and three phase microst ructures were produced, i.e. beside the ordered orthorhombic O phase, the o rdered beta (o) phase (B-2) and the alpha (2) phase (DO19) were determined.