A comprehensive transformation-thermomechanical model on deformation history in directed energy deposition of high-speed steel

Phase transformation is a crucial factor that determines the quality and deformation of components in laser-directed energy deposition (L-DED). Owing to the limitations of in situ observation methods, there is a lack of effective means to study the complete phase transformation and their impacts on deformation during the deposition process. In this study, multilayer heterogeneous deposition was investigated with the high-carbon high-speed steel by modelling the coupled phase transformation-thermomechanical physics. The methodology was proposed to identify the specific phase transformations by iteratively comparing the whole deformation history between digital image correlation (DIC) measurements and simulations. Besides the thermo-mechanical coupling effect and basic volumetric phase transformation, carbon partitioning between precipitated carbides and matrix was manifested, which also resulted in a rise of the Ms point by 208.4 °C and a reduction of the transformation rate by 73.2%. Additionally, an increase of 13.8% in energy absorption could be attributed to the surface oxidation of the deposited layer. The model predictions exhibited good consistency with the DIC in-situ measurement data, indicating that the deformation history contained sufficient information on the phase transformations. Based on the proposed transformation-thermomechanical coupling model, it helps to understand the complete phase transformation during deposition.