Flow stress and dynamic recrystallization behavior and modeling of GH4738 superalloy during hot compression

Abstract

GH4738 superalloy is a key material for gas turbine engines, yet its relatively poor thermoplasticity and narrow temperature range for hot working deteriorate grain structure uniformity and thereafter service performance. Employing hot compression experiments and finite element analysis (FEA), the present study examined the thermoplasticity of the GH4738 alloy and proposed a fast approach to establishing its dynamic recrystallization (DRX) model. The hot working conditions were considered in the 1000–1160 °C temperature range under strain rates of 2–26 s−1 up to a true compressive strain of 0.69. Friction- and temperature-corrected stress-strain curves were obtained, based on which the efficiency of power dissipation and constitutive equations were constructed. It reveals that DRX is the dominant softening mechanism in the GH4738 alloy, where the sensitivity of flow softening positively correlates with lower temperatures and higher strain rates. The appropriate hot working condition for the alloy is temperatures around 1040–1080 °C and a strain rate larger than 8 s−1. The final grain sizes (d) and fractions of DRX (Xdyn) were minimized using the stochastic gradient descent algorithm based on 120 sets of data within the framework of the Avrami equation. It is shown that the formulated model and its integration into the FEA not only yield satisfactory agreement with the experiment but effectively avoid the complexity involved in the traditional method. The study provides key inputs for predicting the flow behavior and grain structure of the GH4738 superalloy, which shall be critical for process development and optimization of industrial manufacturing processes.