Dynamic deformation and failure of Gamma-Met PX at room and elevated temperatures.

摘要

Recently, a new generation of gamma-TiAl alloys, Gamma-Met PX, has been developed. The lack of data on this material and its potential use for aerospace application makes it important to understand its response under different conditions, especially its behavior under dynamic loading capabilities. Studies of bird strike, hard particle impact damage, and fan blade containment within the jet engine during normal and abnormal operations and proper simulations of these events require material properties not only at high strain rates but also coupled with high temperatures. Such materials properties can be obtained from simple geometry laboratory experiments such as those performed in the present study. These experiments include evaluation of material response under dynamic uniaxial loading, dynamic fracture initiation toughness, and shock compression properties.; The compression and tensile tests are conducted using a split-Hopkinson bar apparatus at test temperatures up to 900°C and strain rates of up to 3500s-1. Under uniaxial compression, at temperatures higher than 600°C, thermal softening is observed at all strain rates employed in the present study with the rate of thermal softening increasing dramatically between 800°C and 900°C. The room temperature tensile tests show negligible strain-rate dependence on both yield stress and flow stress. However, the material shows a drop in both yield and flow stress at elevated temperatures. No anomaly in yield stress is observed up to 900°C.; The dynamic fracture toughness initiation study was performed using the modified Hopkinson Pressure Bar. The dynamic fracture initiation toughness was found to decrease with an increase in test temperatures. Moreover, long term elevated temperature exposures were found to be detrimental to fracture toughness.; Normal plate impact experiments were conducted using single stage gas gun to obtain shock properties under uniaxial strain compression. Gamma-Met PX has a Hugoniot Elastic Limit (HEL) of 1.88 GPa at target thickness of 3.86 mm. The decay in the elastic precursor is continuous without showing an asymptotic to a constant value within the range of target thicknesses studied. Under shock compression, Gamma-Met PX showed post yield hardening, however, the impact velocity has little or no effect on the rate of strain hardening. The measured spall strength of Gamma-Met PX was 1.8 +/- 0.09 GPa.