The correlation between the flow behavior and the microstructure evolution during hot working of TC18 alloy

The effects of processing parameters on the flow stress, the strain rate sensitivity and the strain hardening exponent of TC18 alloy are investigated in present study. The isothermal compression is performed in the deformation temperature range of 993-1203K, strain rate range of 0.01-5.0s^-1 and strain range of 0.5-1.2. The micro-mechanisms that might control flow behavior are analyzed using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results demonstrate that the shapes of flow curves are dependent on the competing processes of the work-hardening, the thermal softening and the microstructure-related softening. The maximum m-value of 0.45 occurs at a deformation temperature of 993K, a strain rate of 0.01s^-1 and a strain of 0.5. At 0.1s^-1, the m-value is approximately 0.20-0.27, implying that controlling deformation mechanism is dislocation glide/climb. At a deformation temperature of 1053K and a strain of 0.5, the levels of n-value decrease from 0.01s^-1 and 1.0s^-1, respectively, to 0.1s^-1. The more significant softening effect at 0.1s^-1 is attributed to the medium thermal softening and the microstructure-related softening.