GRX-810: High-temperature behavior, deformation mechanisms, and size effects

GRX-810 is a novel Multi-Principal Element Alloy (MPEA) belonging to the NiCoCr family, primarily strengthened through the Oxide Dispersion Strengthening (ODS) mechanism. This alloy demonstrates high tensile strength and exceptional creep resistance, coupled with significant oxidation resistance, while maintaining remarkable ductility for applications in extreme-temperature environments. Additive manufacturing enabled the development of this alloy by the dispersion of the nano-scale Y₂O₃ throughout the microstructure. However, meeting industrial and production demands requires comprehensive characterization of the microstructure, mechanical and thermophysical properties, as well as variations in geometry and machine parameters. This study investigates the size and temperature-dependent mechanical properties and deformation mechanisms of GRX-810, focusing on the relation between its pristine (pre-deformed) microstructural features and mechanical behavior for elevated temperatures up to 1148 °C. As a medium entropy alloy, GRX-810 benefits from an atomic scale strengthening mechanism and precipitates in the form of carbides and nano-scale yttria oxides, resulting in desirable properties for extreme environment applications. A size-dependent variation in porosity volume, with higher porosity in thinner GRX-810 samples is observed. However, no evidence of size-dependent variation in mechanical properties was identified. Fracture surface analysis revealed deformation twinning through different temperatures, particularly during the later stages of plastic deformation, serving as a strengthening mechanism by delaying necking and fracture. At 537 °C, the Portevin-Le Chatelier (PLC) effect was observed and attributed to lattice distortion impeding dislocation movement. Overall, quasi-static tensile testing demonstrated a progressive linear decrease in yield strength (YS) and ultimate tensile strength (UTS) with increasing temperature, while elongation remained consistently above 30% up to 871 °C for all thicknesses.