Mechanism-Based Models for Predicting the Microstructure and Stress–Strain Response of Additively Manufactured Superalloy 718Plus

Alloy 718Plus, commonly known as ATI 718Plus^®, is a Ni-based superalloy that has been developed to exhibit a γ + γ′ microstructure with a higher high-temperature strength capability compared to Alloy 718. In addition to wrought products, Alloy 718Plus has also been processed by additively manufacturing processes via layer-by-layer deposition. Additively manufactured (AM) 718Plus is typically heat-treated using multiple steps in order to provide an optimized microstructure and desired mechanical properties. In this article, mechanism-based heat treatment and constitutive models were developed for Alloy 718Plus. In particular, solution treatment and aging models were developed for predicting the grain size and the size, number density, and volume fraction of δ, secondary γ′, and tertiary γ′ precipitates in the microstructure. This microstructural information was then utilized in conjunction with a physics-based constitutive model, called MicroROM, to predict the stress–strain response of Alloy 718Plus. The predictive capabilities of the heat treatment models, named HTM718Plus, and the constitutive model (MicroROM) were first benchmarked against literature data of ATI 718Plus. Subsequently, the heat treatment models and constitutive model were applied to predict the microstructure and tensile response of AM 718Plus heat-treated by a multi-step procedure with good agreement between computed results and experimental data.