Wear resistance and characterization  of borided Ni-based alloys

Abstract

In this study, nickel-magnesium (Ni–Mg) alloys with a 97% Ni–3% Mg compositions were successfully borided with packet boriding at temperatures from 900 to 1000 °C and treatment time 1.5–4.5 h. The properties, surface roughness, and density of the resulting boride layers were determined by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and microhardness tests. XRD analysis revealed NiB, Ni₃B, and Ni₂B phases after boriding. The coated boride layer in the alloy resulted in a smooth, dense SEM-approved property. In Ni–Mg alloys, the diffusion of boron atoms from the surface to the matrix accelerated with increasing temperature and treatment time. As such, boride layer thicknesses increased. It has been observed that Mg does not prevent the diffusion of the boron atom. Based on the treatment time and temperature, the thickness of the boride layer of the NM alloy varied between 96.74 and 248.36 μm. The hardness of the boride layer ranged between 1675 and 1832 HV_0.05 for the Ni–Mg alloy, while the Vickers hardness value of untreated nickel amounted to 98 HV_0.05. The surface roughness of Ni–Mg alloys ranged between 0.25 and 0.58 µm, and its densities were 8.4–8.68 g/cm³. Surface roughness values increased with increasing boride layer thickness. The wear tests were carried out in a ball–disc arrangement under dry friction conditions at room temperature with an applied load of 10 N and a sliding speed of 0.3 m/sec at a sliding distance of 250 m. The coefficient of friction of the borided Ni–Mg alloys ranged from 0.42 to 0.64, while that of the unborided alloys was 0.86. It was observed that the wear rate of borided and unborided Ni–Mg alloys ranged from 21.86 × 10^–5 mm³/N × m to 89.92×10^–5 mm³/N × m.