A phase field formulation of the coupled effects of defect generation and large strains on microstructure evolution during laser-based additive manufacturing

A thermodynamically consistent phase field model accounting for coupled effects of large strains, heat diffusion and atomic defect (vacancy and interstitial atom) generation at moving liquid-solid interface is presented to describe microstructure development during laser powder-bed fusion additive manufacturing (AM) of metals. Our model equations, including the Ginsburg-Landau equation for the phase field with stress terms, diffusion-drift Cahn–Hilliard equation, describing atomic defect dynamics, an energy balance equation for the temperature change, and finally the elasticity equation for the displacement fields are derived under a thermodynamic frame based on entropy generation. To describe the effects of temperature gradient and fluid velocity distributions and thermal history on the defect dynamics during microstructure formation a linking of microscale model with the macroscopic AM processing conditions is discussed. Then isothermal equilibrium situation is considered to study diffusion-flexural instability due to defect-strain positive feedback in nanolayers with surface elasticity effects. The influence of defect clustering due to this instability on the periodic exfoliation of deposited layers on a substrate is also discussed.