Understanding the Hot Working Behavior of a Ni-Base Superalloy XH 67 via Processing Map Approach

Hot deformation behavior of nickel-based superalloy XH 67 (Ni-18.5Cr-4.5Mo-4.5W-3.0Fe-2.5Ti-1.2Al) was investigated in the temperature range of 900 degrees C-1,200 degrees C and in the strain rate range of 10(-3)-10 s(-1). A processing map was generated from the flow stress data. Detailed postdeformation microscopy was carried out to understand the microstructural evolution during hot deformation. Correlation of the kinetic analysis together with microstructural characterization studies was accomplished to identify the rate controlling mechanism. An increase in the fraction of Sigma 3 boundaries is observed with an increase in the strain rate at 1,150 degrees C. In the temperature range of 1,100 degrees C-1,200 degrees C, discontinued dynamic recrystallization has been identified as the major softening mechanism. Based on the critical analysis of the mechanical data together with microstructural analysis, the safe hot working regime for the XH 67 alloy is established to have a temperature range of 1,100 degrees C-1,200 degrees C and a strain rate range of 10(-3) to 5 x10(-2) s(-1).