Impact of intragranular misorientation on void swelling and inter-granular cavities after ion irradiation in standard and additive manufacturing 316L austenitic steels

Abstract

Additive manufacturing (AM) is a promising technology for the design of materials with complex geometries with reduced cost and material waste. In order to be used in the nuclear industry, the capability of AM materials, in term of radiation resistance must be compared with materials elaborated in conventional ways. In this work, the radiation resistance of 316L austenitic stainless steels (ASSs) elaborated by AM is compared to a solution-annealed 316L ASS after irradiation with 5 MeV Fe5+ for 3 dpa at 550 °C (873 K). After irradiation, cavities are mainly located near grain boundaries for all studied alloys. Intra-granular cavities are only found in the AM material after heat treatment and are likely to be remaining porosity already present before irradiation. No cavities in intra-granular position are found in the conventional 316L ASS or in the AM material after hot isostatic pressing (HIP) at 1100 °C. It suggests that the void swelling ASSs starts by the formation of cavities at grain boundaries followed by a formation of cavities in intra-granular position, conventionally studied. Loops in the AM material with a hot treatment at 700 °C are heterogeneously distributed due to a bimodal distribution of grains in terms of intra-granular misorientation. The intra-granular misorientation drastically reduces the loop density after irradiation. Frank and perfect loops are found to be only interstitial-type loops. The larger cavities’ size and the more advanced dislocations network in the AM HIP sample suggests a slightly reduced radiation swelling resistance for the AM material but further investigations at higher irradiation dose have to be done.