Selective Laser Melting (SLM) shows a big potential among metal additive manufacturing (AM) technologies. However, the large thermal gradients and the local melting and solidification processes of SLM result in the presence of a significant amount of residual stresses in the as built parts. These internal stresses will not only affect mechanical properties, but also increase the risk of Stress Corrosion Cracking (SCC). A twister used in an air extraction pump of a condenser to create a swirl in the water, was chosen as a candidate component to be produced by SLM in 316 L stainless steel. Since the main expected damage mechanism of this component in service is corrosion, corrosion tests were carried out on an as-built twister as well as on heat treated components. It was shown that a low temperature heat treatment at 450˚C had only a limited effect on the residual stress reduction and concomitant corrosion properties, while the internal stresses were significantly reduced when a high temperature heat treatment at 950˚C was applied. Furthermore, a specific stress corrosion sensitivity test proved to be a useful tool to evaluate the internal stress distribution in a specific component.

Additive manufacturing (AM) is currently one of the most promising and advanced tools to make high-end components. For industrial acceptance of these components, there is a demand for the delivery of high quality parts, certified under recognized standards. Pre-requisites for such certified parts are the certification of the powder feed-stock and the use of qualified facilities. Such a certification and qualification project encompasses different challenges regarding both powder testing and print process stability. Today there are insufficient quantitative acceptance criteria for AM metal powders in the standards. The main challenge is determining which properties to test and how to define some key indicators that can guarantee consistent quality of the end product. To face this challenge several relevant powder properties were tested in order to link powder performance to the properties of the printed material. To guarantee process stability and repeatability, a good knowledge and control of the different process parameters and their influence on the material quality is needed. Hence, an extensive study on the homogeneity of properties over the 3D printer platform was performed. A qualification testing platform was designed to guarantee and periodically check the quality of the printed AM316L material. The proper procedures and parameter settings were determined and fixed. This methodology finally lead to the qualification of the ENGIE Laborelec Powder Lab and the ENGIE Fabricom AM printing facility and the certification of AM 316L material through a recognized external qualification body. This initiative paves the way to ensure industrial acceptance of the selective laser melting process for high quality applications.