Dynamic Fracture Initiation Toughness of a Gamma (Met-PX) Titanium Aluminide at Elevated Temperatures

Recently, a new generation of titanium aluminide alloy named Gamma-Met PX (GKSS, Geesthacht, Germany) has been developed with better rolling and postrolling characteristics. Previous work on this alloy has shown the material to have higher strengths at room and elevated temperatures when compared with other gamma titanium aluminides. In particular, this new alloy has shown increased ductility at elevated temperatures under both quasistatic and high-strain-rate uniaxial compressive loading. However, its high-strain-rate tensile ductility at room and elevated temperatures is limited to ~1 pct. In the present article, the results of a study investigating the effects of the loading rate and test temperature on the dynamic fracture initiation toughness in Gamma-Met PX are presented. A modified split Hopkinson pressure bar (MSHPB) was used along with high-speed photography, to determine the dynamic fracture initiation toughness. Three-point-bend fracture tests were conducted at impact speeds in the range 1 to 3.6 m/s and at test temperatures up to 1200 C. Furthermore, the effect of long-time high-temperature air exposure on the fracture toughness was investigated. The results show that the dynamic fracture initiation toughness decreases at test temperatures beyond 600 C. Moreover, the dynamic fracture initiation toughness was found to decrease with increasing exposure time. The reasons behind this drop are analyzed and discussed.