Controlling the microstructural evolution generated under Additive Manufacturing (AM) conditions is a key aspect to achieving the target mechanical properties. In the present study, an integrated thermomechanical and microstructural simulation of ΑΜ, as applied to an AISI 316L austenitic stainless steel, is presented. A one-way coupled analysis is carried out with the heat transfer, microstructural and mechanical problems solved in sequence. A ﬁnite element technique is employed to evaluate the temperature evolution as well as residual stresses and distortions in the processed part, due to the successive material deposition. The material deposition is modelled using quiet elements which are activated as the added material solidifies. These elements are present from the start of the analysis but are assigned properties so they do not affect the analysis. The thermal history generated by two-dimensional heat transfer simulations which is essential in determining the resulting microstructure. The effect of processing parameters on critical microstructural features such as freezing range, phase fractions, and elemental segregation were investigated via CALPHAD-based computational thermodynamic and kinetic modelling, implemented in the Thermo-Calc software. Two limit cases of equilibrium and instantaneous solidification were studied through thermodynamic calculations and the Scheil-Gulliver model. Kinetic analysis followed, using the complete thermal cycle calculated by heat transfer simulations. Solidification and solid-phase transformations were investigated upon thermal cycling via multi-phase and multi-component diffusion simulations. A distinction between eutectic and peritectic solidification modes was made, as both have been observed in AM studies. Model comparison carried out, in agreement with experimental observations, indicated that the peritectic diffusion model resulted to the highest freezing range and the smallest ferrite fraction. The ensuing microstructural properties, including phase fractions and constitutions, as well as the temperature field are provided as an input for a mechanical analysis, to calculate the residual stresses and distortions.
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Microstructural and thermomechanical simulation of the additive manufacturing process in 316L austenitic stainless steel
Published: 18 February 2021 by MDPI in The 1st International Electronic Conference on Metallurgy and Metals session Additive Manufacturing
Keywords: Additive manufacturing; 316L stainless steel; solidification; microsegregation; finite elements; simulation