Hot deformation behavior and process parameters optimization of GH4738 nickel-based superalloy

The GH4738 nickel-based superalloy exhibits exceptional overall performance at high temperatures. However, its high deformation resistance, narrow hot working window, and complex microstructural evolution pose significant challenges to plastic deformation of the alloy. Hot compression experiments were conducted on the GH4738 nickel-based superalloy using a Gleeble 3800-GTC thermal-mechanical physical simulation system. The hot deformation behavior of the alloy was systematically investigated across deformation temperatures ranging from 950 to 1150 degrees C and strain rates from 0.01 to 10 s-1. The analysis of the true stress-strain curves revealed the effect of deformation parameters on the flow stress of the alloy. The flow stress was highly sensitive to both strain rate and deformation temperature, increasing with higher strain rates or lower deformation temperatures. Based on the experimental data, a high-precision peak stress prediction model and an Arrhenius constitutive model considering strain compensation were established. In addition, processing maps for the alloy were constructed based on the dynamic materials model (DMM) and Prasad's instability criterion. Coupled with microstructural observations and validation, the flow instability of the alloy was manifested as flow localization and adiabatic shear bands (ASBs), while the deformation mechanism in the safe region was characterized by discontinuous dynamic recrystallization (DDRX). Ultimately, the optimal hot working process windows for the alloy were determined to be 1010-1075 degrees C/0.01-1 s- 1 and 1075-1150 degrees C/0.03-1 s- 1.