Characterization of structural and mechanical properties of HfNbTaTiZr refractory high entropy alloy after gas nitriding

This study was initiated to improve surface hardness and wear resistance of a HfNbTaTiZr refractory high entropy alloy (RHEA) by gas nitriding at a medium temperature (600 °C) for 3 h. Structural characterizations conducted by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) equipped scanning electron microscope (SEM) revealed that nitriding led to formation of a 1.5 μm thick surface layer containing precipitates of oxides and nitrides of the alloying elements. Detection of oxides within the surface layer was attributed to the presence residual oxygen in the nitriding atmosphere. Nevertheless, the employed gas nitriding provided remarkably higher scratch resistance compared to the untreated state, as the results of increment in the surface hardness and development of larger compressive residual stress.