Forming and fracture limits of IN718 alloy at elevated temperatures: Experimental and theoretical investigation

Forming and fracture forming limit diagrams are significant performance indexes for evaluating the formability of a material. In the present study, experimental and theoretical investigations of the forming and fracture behavior for precipitate-hardenable Inconel 718 superalloy, have been performed at different temperatures (Room temperature (RT) to 700 degrees C). Firstly, uniaxial tests have been conducted over a temperatures range and quasi-static strain rates (10(-4)-10(-1)s(-1)). Flow stress (tensile) has been found to be significantly affected by variation in test temperatures and strain rates. Further, yielding behavior of IN718 alloy has been predicted based on Hill'48 (r and s based) and Barlat'89 criteria. Barlat'89 criterion has better predictability of yielding behavior for IN718 alloy at all test temperatures. Subsequently, experimental forming and fracture limit curves have been plotted at different temperatures using Nakazima test. Limiting true strains have been found to be increasing with test temperature for all deformation regions in forming limit diagrams. Marciniak Kuczynski (M-) and Bao-Wierzbicki (B-W) model coupled with anisotropic yield criteria have been used for theoretical prediction of limiting and failure strains for IN718. The M-K and B-W models coupled with only Barlat'89 criteria have shown a good prediction ability of limiting strains with least root mean square error (RMSE) and average absolute error (AAE).