Micromechanical assessment and thermophysical characterization of HSS M4 deposits processed by Laser Metal Deposition, - a prerequisite to the validation of a thermomechanical model

Additive manufacturing is a material-processing technique that is expanding rapidly, with applications in various fields such as repair technology under thin or thick deposits, or the development of complex shaped parts.
In this work, the phases present in Tool steel AISI HSS M4 deposits obtained from Laser Metal Deposition (LMD) are identified using two characterization techniques i.e. hardness and dilatometry. The first technique is static and it is used at different scales, starting from macroscale with Vickers hardness down to nanoscale with nano-indentation. The second technique is dynamic, and it is used under different scanning rates upon heating or cooling. Light microscopy is also used to complete the microstructural characterization. In addition, a validated thermal model has been used to obtain simulated thermal histories within the deposit during LMD processing [1]
It is established that the hardness in the deposit varies according to the local thermal history, which influences the martensitic or bainitic nature of the matrix. For dilatometry, it is shown that both the nature of the phases and the solid state transformation mechanisms (diffusive or displacive) are strongly influenced by heating/cooling rates.
Knowing the microstructure and its related thermophysical properties provide input parameters for thermomechanical models, which are useful for predicting in-process behavior, as illustrated by the evolution of the deformation of a beam substrate during the deposition of a HSS M4 thin wall by a LMD process.
[1] R. T. Jardin et al., Mat. Let. 236 (2019)