Fabrication of ODS Austenitic Steels and CoCrFeNi High-Entropy Alloys by Spark Plasma Sintering for Nuclear Energy Applications

Candidate materials for advanced nuclear energy systems, i.e., oxide-dispersion-strengthened (ODS) austenitic steels and CoCrFeNi high-entropy alloys (HEAs), have been fabricated by spark plasma sintering (SPS). Microstructures of ODS alloys have been characterized by transmission electron microscopy and electron backscatter diffraction, revealing that Y-Ti-O particles with an average particle size of 7.6 nm are homogeneously distributed in the austenite steel matrix with an average grain size of 985 nm. The fine microstructure of ODS austenitic steels is thermally stable after annealing at up to 1100°C. The high strength and hardness of ODS austenitic steels may be attributed to grain boundary strengthening as well as dispersion strengthening. The effect of powder processing and SPS parameters on the microstructural formation in CoCrFeNi HEAs has also been investigated. CoCrFeNi HEAs have a single-phase face-centered cubic (FCC) structure and a homogeneous distribution of four metal elements. The mechanical alloying powders have a mixture of FCC and body-centered cubic phases, which is transformed to FCC phase after SPS at 900–1000°C. CoCrFeNi HEAs fabricated from mechanical alloying powders have a smaller grain size and higher concentration of chromium- and oxygen-rich precipitates than those fabricated from gas-atomized powders, resulting in a higher hardness.