Influence of manufacturing parameters on microstructure and subsurface residual stress in SLM Ti-6Al-4V

Abstract

Using non-optimum combination manufacturing parameters in selective laser melting (SLM) may lead to reduction of quality of component: defects generation, distortion of geometry and even cracking. Usually, the optimization of parameters is performed at first with the goal to minimize porosity values, which are easy to measure. However, not only low porosity but also a stable microstructure and low residual stresses will help to achieve the desired mechanical behavior of the material and, thus, the component. In present work, we investigated cuboid-shaped Ti-6Al-4V samples produced with different manufacturing parameters. Residual stresses in subsurface region were investigated by synchrotron X-ray diffraction, which allows to penetrate around 100 µm into the surface and therefore to overcome the problem of high roughness of SLM components without additional sample preparation and resulting artifacts. Only tensile stresses were found along the building direction that can play critical role especially during cyclic loading. The pore shape and spatial distribution obtained by computed tomography varied for samples produced with the same Ev. Importantly, by adjusting specific process parameters it was possible to decrease residual stresses while at the same time obtaining a uniform α+β Ti microstructure and relatively low porosity.