Effect of boriding process temperature on microstructure, mechanical properties, and wear behavior of Al0.25CoCr1.5FeMo0.5Ni HEA

Abstract

This study comprehensively investigates the effects of package boriding temperature on the microstructure, mechanical, and tribological properties of a high-entropy Al0.25CoCr1.5FeMo0.5Ni alloy. The treatments were conducted at 875 degrees C, 950 degrees C, and 1025 degrees C for five hours in a powder environment commonly used in industrial surface modifications. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) were used for microstructural characterization. Cross-sectional analyses revealed the thickness and morphology of the boride layers. While the alloy initially consisted of FCC + sigma phases, the boriding process promoted the formation of complex boride layers on the surface. The layer thickness increased with temperature, reaching approximately 14 mu m at 875 degrees C, 19 mu m at 950 degrees C, and 70 mu m at 1025 degrees C. Mechanical behavior was evaluated using microhardness and nanoindentation tests. Surface hardness increased from 10.8 GPa to 25.1 GPa with increasing temperature, and significant increases were observed in the elastic modulus, H/E, and H3/E2 ratios. These results indicate that the boronized surface is more resistant to plastic deformation and responds more elastically under load. Wear tests conducted under dry sliding conditions confirmed that boronizing reduces material loss by over 90%. The highest wear resistance was achieved in samples boronized at 1025 degrees C. Overall, the boride layer formed a strong barrier on the surface, effectively suppressing wear and surface damage. As a result, the package boronizing process significantly increased the surface strength of the alloy and demonstrated its potential for use in components operating at high temperatures.