Failure behaviors and processing maps with failure domains for hot compression of a powder metallurgy Ni-based superalloy

TL;DR

This study investigates failure behaviors during hot compression of a powder metallurgy Ni-based superalloy, employing experiments and finite element analysis to develop processing maps with failure domains for improved thermo-mechanical processing guidance.

Contribution

It introduces a novel approach combining experimental data and FEA with a damage model to delineate failure domains in processing maps for Ni-based superalloys.

Findings

Failure initiates at outer surfaces due to maximum tensile stress.

Failure strain is strain-rate independent and increases with temperature.

An optimized processing window is proposed to ensure good workability and avoid failure.

Abstract

Processing maps are key to guiding the thermo-mechanical processing (TMP) of superalloys. However, traditional processing maps are incapable of delimiting failure, which is an essential factor to be concerned about during the TMP of superalloys. Employing isothermal hot compression experiments and finite element analysis (FEA), the present study examined the failure behaviors of a powder metallurgy (P/M) Ni-based superalloy and constructed processing maps with failure domains based on the predicted failure threshold. The micromechanical Gurson-Tvergaard-Needleman (GTN) damage model was employed in the FEA to model the cavity-driven intergranular fracture of the superalloy. Deformation temperature and strain rate were considered in the range of 1050 ~ 1150 C and 0.001 ~ 1 s-1, respectively. The FEA results reveal that the maximum tensile stress locates at the outer budging surfaces of the samples, which causes failure initiation and subsequent propagation into longitudinal cracks, being consistent with the experiments. It is further demonstrated that the failure is strain-controlled and the critical failure strain remains nearly insensitive to the range of strain rates considered while increasing with the increase of temperature in a third-order polynomial. Finally, an optimized processing window for hot deformation of the superalloy is formulated to warrant good hot workability while avoiding flow instability and failure. The present study offers direct insights into the failure behaviors of P/M Ni-based superalloys and details a modeling strategy to delineate optimized parametric spaces for the TMP of superalloys.