Mitigation of residual stresses and microstructure homogenization in directed energy deposition processes

Abstract

In additive manufacturing (AM), residual stresses and microstructural inhomogeneity are detrimental to the mechanical properties of as-built AM components. In previous studies, the reduction of the residual stresses and the optimization of the microstructure have been treated separately. Nevertheless, the ability to control both them at the same time is mandatory for improving the final quality of AM parts. This is the main goal of this paper. Thus, a thermo-mechanical finite element model is firstly calibrated by simulating a multi-track 40-layer Ti–6Al–4V block fabricated by directed energy deposition (DED). Next, the numerical tool is used to study the effect of the baseplate dimensions and the energy density on both residual stresses and microstructure evolution. On the one hand, the results indicate that the large baseplate causes higher residual stresses but produces more uniform microstructures, and contrariwise for the smaller baseplate. On the other hand, increasing the energy density favors stress relief, but its effect fails to prevent the stress concentration at the built basement. Based on these results, two approaches are proposed to control both the stress accumulation and the metallurgical evolution during the DED processes: (i) the use of a forced cooling suitable for small baseplates and, (ii) the adoption of grooves when large baseplates are used. The numerical predictions demonstrated the effectiveness of the proposed manufacturing strategies.