Mechanical properties and dislocation substructure of inconel 690 alloy impacted at cryogenic temperatures

The mechanical response and dislocation substructure of Inconel 690 during impact deformation are investigated at strain rates of 2 × 10³ ∼ 6 × 103 s-1 and temperatures of -150°C, 0°C and 25°C using a compressive split-Hopkinson pressure bar system. The results show that the flow stress, work hardening rate and strain rate sensitivity all increase with increasing strain rate or decreasing temperature. By contrast, the activation volume reduces as the strain rate increases or the temperature decreases. Moreover, the temperature sensitivity increases with both increasing strain rate and increasing temperature. Optical microscopy observations show that adiabatic shear bands are formed at the highest strain rate of 6 × 10³ s-1 in all of the tested specimens. In addition, it is shown that adiabatic shear localisation is the major cause of specimen failure in every case. The dislocation density increases, and the cell size decreases, as the strain rate is increased or the temperature decreased. The change in the dislocation density and cell size is found to have a significant effect on the flow stress and work hardening behaviour of the Inconel 690 specimens; particularly at high strain rates or low temperatures.