Abstract
During selective laser sintering (SLS), the microstructure evolution and local temperature variation interact mutually. Application of conventional isothermal sintering model is thereby insufficient to describe SLS. In this work, we construct our model from entropy level, and derive the non-isothermal kinetics for order parameters along with the heat transfer equation coupled with microstructure evolution. Influences from partial melting and laser-powder interaction are also addressed. We then perform 3D finite element non-isothermal phase-field simulations of the SLS single scan. To confront the high computation cost, we propose a novel algorithm analogy to minimum coloring problem and manage to simulate a system of 200 grains with grain tracking algorithm using as low as 8 non-conserved order parameters. Specifically, applying the model to SLS of the stainless steel 316L powder, we identify the influences of laser power and scan speed on microstructural features, including the porosity, surface morphology, temperature profile, grain geometry, and densification. We further validate the first-order kinetics of the transient porosity during densification, and demonstrate the applicability of the developed model in predicting the linkage of densification factor to the specific energy input during SLS.
Highlights
Selective laser sintering (SLS) is a typical additive manufacturing (AM) process meant for rapid prototyping and tooling.[1–5] DuringSLS, a desired geometry is built by sequentially layer-by-layer powder spreading and subsequent sintering driven by laser scan.[6,7] To be distinguished with the other laser-based powder bed additive manufacturing known as selective laser melting (SLM), there is no significant melting phenomenon during SLS
We explicitly discuss the influences from laser power and scan speed on features such as the temperature profile, geometry, and corresponding sintering stages of particles/ grains, and microstructure densification
Temperature profile in SLS is directly related to the processing parameters
Summary
Selective laser sintering (SLS) is a typical additive manufacturing (AM) process meant for rapid prototyping and tooling.[1–5] During. We obtain a free energy density functional with temperaturedependent heat, local, and gradient terms through Legendre transformation, which is frequently used in thermodynamics analysis for non-isothermal conditions.[36,44,45] Such formulation is able to reproduce the temperature-induced inhomogeneity of surface and grain-boundary energies, and their influences on kinetics, e.g. the mass transfer induced by inhomogeneity of surface.[43]. Without introducing OPs to indicate the melting/ solidifying processes, the latent heat L would only influence the local thermodynamic stability along with the heat term Those model parameters, as well as the gradient constants (κρ and κη), are obtained from experimental measurements of the temperature-dependent surface and grain-boundary energies (γsf and γgb), and the grain boundary width. Ept and scf should consider the temperatureindependent potentials and configuration entropy among atmo-
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