Lightweight, High Temperature Beta Gamma Alloy/Process Development for Air Frame Structure Applications

Gamma titanium aluminide alloys (gamma alloys) possess the attractive combination of low density (~50% of that of superalloys) and high temperature (up to 1500°F) capability, ideal for hot airframe structure and turbine engine applications. Yet, gamma alloys have not been inserted into aerospace service due to their material and manufacturing limitations. The primary limitations include processing difficulties, requiring costly non-conventional or multi-step processing requirements, and large lamellar grains, often leading to lowered damage tolerance. We have developed a new class of TiAl-based alloys, called beta gamma, which would remove or reduce such barriers. Unlike existing gamma alloys, beta gamma alloys are designed such that the ductile beta phase is adequate at elevated temperatures (for processing) but low or negligible at the anticipated use temperatures (for performance). The alloys also feature significant grain refinement and compositional homogeneity. This program is aimed to utilize such beneficial beta-phase distribution and microstructure features to develop the process technology to produce low-cost beta gamma alloy mill products such as thin sheets and rectangular bars with potentially improved properties. These low-density (4.1g/cm3) products are expected to be used at least up to 1300°F, showing application potential for airframe and engine structures.