Controlling melt pool shape, microstructure and residual stress in additively manufactured metals using modified laser beam profiles

Abstract

Laser powder bed fusion has proven to be an effective additive manufacturing technology for the manufacture of complex metal components. However, the local thermal history associated with Gaussian beam, raster scan processes produces heterogeneous and spatially non-uniform microstructures that differ from those produced from conventional manufacturing and often lack optimized mechanical properties. Steep thermal gradients and high cooling rates produce large thermal strains driving residual stress fields that can negatively affect the dimensional accuracy of the as-built component. Here, we present experimental and simulation methods for controlling microstructure and residual stress through tailored laser beam profiles. Elliptical and Bessel beam profiles are shown to produce more equiaxed microstructures as compared to those of Gaussian beams, while distributed diode-based illumination profiles allow for reduced residual stresses. These experimental results are supported by high-fidelity powder-scale simulation models coupled to the cellular automata and thermomechanical models that account for macroscale residual stress.