Efficacy of semi-empirical models for prediction of forming limit curve of IN718 alloy at elevated temperatures

Abstract

ABSTRACT Inconel 718 alloy (IN718) is a high-strength material and is widely used in aerospace and nuclear applications for extreme working conditions. IN718 alloy is difficult to form at room temperature (RT) conditions. Warm/hot forming is used as an alternative approach for forming of complex shape components for IN718 alloy. The present study is focused on the influence of processing temperatures (RT, 400°C and 700°C) on the formability of IN718 alloy. Experimental forming limit curves (FLCs) have been plotted at different temperatures using standard Nakazima test. Improvement in maximum major safe strain values for T-C (tension–compression) and T-T (equi-biaxial tension) region is found to be 54.35% and 66.16%, respectively, at 700ºC. Further, the effect of processing temperatures on surface strain distribution, thickness distribution and limiting dome height (LDH) is also analysed. Surface strain distribution at test temperature mainly depends on strain path throughout stretching. LDH is increased by approximately 33–44% at 700ºC. FLCs are predicted based on Paul and Chow semi-empirical models based on uniaxial anisotropic properties and Hosford’s constants. The predicted FLCs are validated with experimental FLCs based on average absolute error (AAE). Predicted FLCs by Paul method show good agreement with experimental limiting strains.