Microstructure and Mechanical Behavior of ODS Stainless Steel Fabricated Using Cryomilling

Abstract

Oxide-dispersion-strengthened (ODS) stainless steels have been developed as structural materials for applications at elevated temperatures. In this study, water-atomized 316L stainless steel powder was cryomilled with various types of nanosized-oxide reinforcements. Conventional sintering and field-assisted sintering techniques (FAST) were used to consolidate the cryomilled powder. Mechanical properties, both in tension and compression, were evaluated for consolidated samples: samples made of cryomilled powders, as well as samples made of a mixture of cryomilled and coarse-grained atomized powders. The bimodal structure that evolved from such mixtures effectively toughened the ultrastrong cryomilled material. Microstructural analysis was carried out to determine the efficacy of the cryomilled powder. Results from the cryomilling experiments showed that a minimum grain size could be reached within 12 hours of milling. Our results showed that dispersion of the oxide phases during cryomilling occurred exclusively through physical mechanisms, which was different from that previously reported for room-temperature ball milling. The spatial distribution of the oxide dispersoids was found to be dependent on the evolution of internal surfaces during milling and on the type of oxide particle used. Finally, the influence of reinforcement on the mechanical behavior of the cryomilled material was analyzed using oxide-dispersion-strengthening and load-transfer-based strengthening mechanisms.