Thermo-physical phase field model of laser powder melting additive manufacturing of 2D layered stainless steel structures

Abstract

Additive manufacturing (AM) techniques based on laser melting of metal powders are experiencing tremendous growth and are rapidly becoming the preferred processing approach for metal parts. However, the effect of the different processing variables on microstructural and mechanical property outcomes is not yet fully understood. Modeling and simulation can provide an inexpensive and expedient way to probe the large parameter space and identify the most important correlations between processing degrees of freedom and output products. In this work, we develop a two dimensional thermo-physical phase model of laser melting additive manufacturing that captures solidification and melting, heterogeneous nucleation, and oriented grain growth to simulate layered microstructures grown by melting a metal layer connected to the underlying substrate by a set of orientation relations. The model solves the Allen-Cahn and heat diffusion system of equations on structured meshes, and simulates the motion of a laser spot across the specimen through a sequence of successive passes. The simulations best replicate the formation of columnar structures, as under high-power laser conditions or under rapid solidification kinetics, in good qualitative agreement with experimental observations. Our approach connects processing variables with the microstructural outcomes, thus capturing the effect of important inputs such as laser spot size, laser scan speed, and cross hatch fraction on grain size and structure.