Cyclic mechanical response of LPBF Hastelloy X over a wide temperature and strain range: Experiments and modelling

Additive manufacturing (AM) of high-temperature alloys through processes such as laser powder bed fusion (LPBF) has gained significant interest and is rapidly expanding due to its exceptional design freedom, which enables the fabrication of complex parts that contribute to the increased efficiency of aerospace and energy systems. The materials produced through this process exhibit unique microstructures and mechanical properties, which necessitate dedicated study and characterization. In this context, our research focuses on the experimental characterization of the isothermal cyclic viscoplastic mechanical response of Hastelloy X (HX) over the temperature range of 22 to 1000 °C and at various strain rates, addressing a current gap in the literature. Recognizing the need for material models that can accurately represent the cyclic mechanical response of LPBF HX across a broad temperature range, we developed a robust extension of the viscoplastic isotropic-kinematic hardening Chaboche model, intended for applications in the thermomechanical simulation of the LPBF process for the analysis of residual stress and distortion, as well as for assessing the mechanical integrity of LPBF components. The extension involves expressing the entire set of model parameters explicitly with analytical functions to account for their temperature dependence. Consequently, the model includes a relatively large number of parameters to represent the isotropic-kinematic hardening viscoplastic response of the alloy over a wide temperature range, and hence to overcome the endeavor of its systematic calibration, a dedicated calibration approach was introduced. The model ultimately demonstrated its capability to precisely represent the isothermal response of the alloy over the examined temperatures and strain rates. To evaluate the model's predictiveness for non-isothermal conditions, out-of-phase thermomechanical cyclic experiments were also conducted as independent benchmark tests, where the model's predictions were fairly consistent with the experimental results. As a part of this study, the derived material model has been integrated into the UMAT subroutine, complete with an analytical derivation of the consistent Jacobian matrix.