Microstructural evolution and mechanical behavior of oxide dispersion strengthened steel formed by laser selective melting

Abstract

In recent years, nuclear fusion has been explored as a prospective solution to the world’s energy needs. Materials for fusion reactors need to withstand high temperatures and high radiation levels, and materials such as tungsten and reduced activation ferrite/martensite (RAFM) steel have been proposed as possible materials for plasma-facing components. In this paper, RAFM steel is investigated and a new fabrication method is proposed. RAFM steel powder doped with 0.5wt. % Y2O3 particles (ODS-RAFM steel) were manufactured by selective laser melting (SLM). The samples were normalized and tempered. An analysis was conducted to examine the impact of Y₂O₃ particles on the microstructure and properties of the RAFM steel. X-ray diffraction analysis of the phase composition of ODS-RAFM steel (primarily Fe-Cr) showed that grains in the (110) orientation increased significantly after heat treatment. Examination of the microstructure of the ODS-RAFM steel showed a small number of micro-cracks along the grain boundaries, which was mainly related to the high melting point oxides. The interface between Y2O3 and the matrix was prone to stress concentration during the forming process, and the direction of crack expansion was perpendicular to the lath boundaries. TEM micromorphology revealed that MX carbonitride and Y-Ta-O oxides were dispersed throughout the matrix. Few M23C6 particles demonstrated the carbon atoms bonded more strongly with Ta and V atoms. Precipitations could pin the dislocation effectively and play a key role in improving the strength of ODS-RAFM steel. The improvement in mechanical properties reflects the change in microstructure, where the grain boundary strengthening and Orowan strengthening plays a key role. This paper finds that the performance of RAFM steel can be improved by the addition of Y2O3 nanoparticles using additive manufacturing, which provides a theoretical basis for further development of structural materials for future nuclear fusion devices.