Study on structure evolution of CoCrFeNi high entropy alloy in containerless processing using neutron diffraction

Abstract

Containerless processing is able to access the deeply supercooled regime due to the absence of heterogeneous nucleation sites, for example, container walls. Therefore, it allows us to explore a possible structural transition in the supercooled state, which is usually hidden by crystallization and difficult to detect with conventional methods. CoCrFeNi high entropy alloys (HEAs) were solidified in aerodynamic levitation containerless processing in Nanoscale-ordered Materials Diffractometer (NOMAD) BL-1B instrument at Spallation Neutron Source (SNS) Oak Ridge National Lab with expectation the distinct local ordering in CoCrFeNi HEAs. The temperature dependence of local structures was investigated from room temperature to 1500 °C on NOMAD. The phase evolution of the CoCrFeNi HEA investigated using in-situ neutron diffraction shows that room temperature face-centered cubic (fcc) phase is inherited from its high-temperature (above 1400 °C) fcc cluster.