Surface treatment of additively manufactured high-alloy austenitic steel parts with the aim of prolonging the fatigue life

Abstract

In this article preliminary results of an interdisciplinary study on high-alloy austenitic steel with medium manganese content X2CrMnNi16-7-4.5 are presented. The specimens were manufactured using the powder-based electron beam melting technology (PBF-EB/M). The steel powder for the PBF-EB/M process was gas-atomised using a vacuum induction-melting gas atomisation (VIGA-1B) unit. For improving the surface integrity of the manufactured specimens, they were plasma electrolytic polished (PEP) in a combination with particle blasting. The bath-PEP and standing-wave-PEP processes were realised. The PBF-EB/M process parameters were also optimised in order to reduce the depth of surface notches of the specimens in as-built conditions as well as minimise the building defects, e.g. lack of fusion. The initial results show that while PBF-EB/M process is well suited for processing X2CrMnNi16-7-4.5 steel. The resulting surface quality requires significant post-treatment efforts for improving its integrity. The efficiency of the used surface enhancement techniques is evaluated in terms of the thickness of the removed material, δ, as well as the material removal rate MRR and by qualitatively evaluating the resulting surface condition. It is demonstrated that standing-wave-PEP holds the promise for being the most effective surface treatment for PBF-EB/M parts. The optimised parameters for manufacturing and post-treatment processes will be applied for fabricating a bottom bracket of a cargo bike that is topology optimised for prolonged fatigue life.