On the applicability of JMAK-type models in predicting IN718 microstructural evolution

Abstract

Nickel-based superalloys are widely used in the aerospace sector for their mechanical properties, which are directly related to the microstructural and physical properties of these materials. JMAK-type models have been applied to this class of superalloys for the prediction of microstructural evolution phenomena such as recrystallisation. However, these models often lack a clear range of applicability. The majority of the successful applications normally address rather idealised processes (relatively slow forging, simple geometry). However, the industrial production environment generally involves complex strain paths and thermal histories. Thus, there arises the question of whether the JMAK-type models can be applied to such cases. This paper's research focus is to investigate the applicability of JMAK-type models for such processes. To do this, screw press forging of disks was used to validate the in-built JMAK-type model of Inconel 718® available in DEFORMTM. In particular, the applicability of the model was examined using a comparison between the results from simulation and from metallographic analysis. At first, the appropriateness of the JMAK outputs in describing the observed microstructures was investigated and then quantitative results were evaluated. The model's outputs were found to be insufficient in describing the observed microstructural states and additional parameters were deemed necessary. The model's predictions ranged from a broadly good match, for which the model could be calibrated with a proposed new methodology, to a qualitative mismatch that highlights the limits of the model's applicability.