Investigation of the effect of boriding process on the wearproperties of CrFeMnNbNi high entropy alloy

In this thesis, a multi-component alloy system was synthesized based on the high-entropy principle, involving at least five different elements in equiatomic or near-equiatomic proportions. Unlike conventional alloys, which typically form solid solutions with limited entropy, high entropy alloys (HEAs) represent a new generation of materials characterized by high configurational entropy and a tendency to form solid solution phases with randomly distributed elements. The CrFeMnNbNi alloy was produced using the vacuum arc melting method, utilizing high-purity (99%) Cr, Fe, Mn, Nb, and Ni elements in the form of ingots. The primary objective of the study was to investigate the effect of boriding on the CrFeMnNbNi alloy and to analyze the resulting microstructural changes. The boriding treatment was conducted at 950 °C for 5 hours. Optical microscopy revealed the presence of characteristic dendritic and interdendritic morphologies in the alloy's microstructure. Elemental distribution was examined using Energy Dispersive Spectroscopy (EDS) in various regions, and possible phase formations were evaluated based on the observed chemical composition ratios. The boriding process led to significant changes in the microstructure, mechanical properties, and wear resistance of the alloy. These changes were analyzed in detail. Thermodynamic evaluations using XRD and SEM analyses identified three primary phases in the alloy's microstructure: Laves phase, FeNi phase, and FeCr phase. Following the boriding process, a metallic boride layer with a thickness of 30–40 µm formed on the surface. This boride layer significantly enhanced the alloy's hardness and residual elastic modulus, increasing them approximately fivefold to reach values as high as 2800 HV. Nanoindentation tests indicated that the Laves phase exhibited the highest hardness and elastic modulus values (10.9–190 GPa), while the FeNi phase had the lowest (2.74–128 GPa). In the boride layer itself, the maximum hardness values were measured in the range of 24–302 GPa. Wear tests demonstrated that boriding substantially reduced wear losses, with reductions of up to 96% observed.