No abstract

No abstract

Purpose -Additive manufacturing technologies such as, for example, selective laser melting (SLM) offer new design possibilities for a wide range of applications and industrial sectors. Whereas many results have been published regarding material options and their static mechanical properties, the knowledge about their dynamic mechanical behaviour is still low. The purpose of this paper is to deal with the measurement of the dynamic mechanical properties of two types of stainless steels. Design/methodology/approach -Specimens for dynamic testing were produced in a vertical orientation using SLM. The specimens were turned to the required end geometry and some of them were polished in order to minimise surface effects. Additionally, some samples were produced in the end geometry ("near net shape") to investigate the effect of the comparably rough surface quality on the lifetime. The samples were tension-tested and the results were compared to similar conventional materials. Findings -The SLM-fabricated stainless steels show tensile and fatigue behaviour comparable to conventionally processed materials. For SS316L the fatigue life is 25 per cent lower than conventional material, but lifetimes at higher stress amplitudes are similar. For 15-5PH the endurance limit is 20 per cent lower than conventional material. Lifetimes at higher stress also are significantly lower for this material although the surface conditions were different for the two tests. The influence of surface quality was investigated for 316L. Polishing produced an improvement in fatigue life but lifetime behaviour at higher stress amplitudes was not significantly different compared to the behaviour of the as-fabricated material. Originality/value -In order to widen the field of applications for additive manufacturing technologies, the knowledge about the materials properties is essential, especially about the dynamic mechanical behaviour. The current study is the only published report of fatigue properties of SLM-fabricated stainless steels.

Key in powder-bed-based additive manufacturing is the use of appropriate powder materials that fit to the process conditions. There are many parameters affecting the build process and the corresponding quality of the parts being built. Therefore, an accurate assessment of the powders becomes important. Such an assessment involves, besides others, the powder flowability, which should be sufficient in order to create good-quality powder layers. The current study aims at the development of suitable parameters and values for the qualification of metal powders for selective laser melting (SLM) with regard to their flowability. The powder flowability is assessed by the statistical analysis of the measured powder avalanche angles and the powder surface fractal, which give valuable information about the significance of inter-particle forces. A set of 21 different Fe-and Ni-based powders has been analysed and good correlations between the powder avalanche angles, the surface fractal and the particle shape with the optically evaluated flowability could be derived. The method allows a quantitative powder flowability assessment, which correlates with the experiences for powders for powder-bed-based additive manufacturing, especially for SLM.