Tensile impact behavior and deformation mechanism of duplex TiAl intermetallics at elevated temperatures

Investigations are made on the effects of strain rates on the tensile behavior and deformation modes of Duplex Ti-46.5Al-2Nb-2Cr (DP TiAl) at temperatures ranging from room temperature to 840 A degrees C and under strain rates of 0.001, 320, 800, and 1350 s(-1). The dynamic strength is higher than quasi-static strength but does not change much over the high strain rate range. Yield stress anomaly is not found. Brittle-to-ductile transition temperature (BDTT) increases with the increased strain rates. A Zerilli-Armstrong constitutive model with appropriate coefficients is chosen to describe the high strain rate flowing behavior. TEM analysis indicates that both ordinary dislocations and superdislocations are found and dislocation pile-up only appears in samples deformed under quasi-static loadings at elevated temperatures. The deformation twins are common in equiaxed grains and the proportion of twinned grains increases with the increased strain rate from 46-72% under quasi-static loadings to 69-95% under high strain rate loadings. No deformation twins are found in lamellar colonies.