Microstruture And Wear Properties Of Nitrided Layer On High-Entropy Alloy

It is generally believed that intermetallic compounds tend to be formed in the alloys as the amount of alloying elements increases,resulting in poor mechanical properties.In recent years,high-entropy alloys?HEAs?have attracted more and more attention from scholars,duo to the outstanding properties and simple crystal structure.Currently,much attention has been paid to optimizing the microstructure and mechanical properties.However,very limited attempts have been carried out to study the surface properties and tribological properties of the HEAs.The as-cast alloys were synthesized by non-consumable vacuum arc furnace.The nitrided layer on alloys were prepared using LDMC-100A plasma nitriding furnace.The friction and wear tests were performed using a ball-on-block high-speed reciprocating wear test apparatus?MFT-R4000?at room temperature,and the wear tests were carried out under the dry sliding condition,deionized water,and the acid rain,respectively.The microstructure and wear surface of the alloys were analyzed using three-dimensional?3D?surface profiler based on scanning white light interferometry,scanning electron microscope?SEM?with an attached X-ray energy dispersive spectrometer?EDS?,X-ray photoelectron spectroscopy analysis?XPS?and X-ray diffractometer?XRD?with Cu K?radiation.The effect of the environmental medium on the friction and wear performances of nitrided layer was discussed in detail.The results showed that:?1?The as-cast Al_1.3CoCuFeNi₂ HEAs had both simple FCC and BCC solid solution phase.Al N and Fe₄N phases were observed on the surface of the nitrided alloys.The hardness values of the as-cast and nitrided HEAs were 340 HV and587 HV,respectively.?2?The wear rate of as-cast alloys in the deionized water was lower than that in the air and acid rain.The average friction coefficient and wear rate of the nitrided alloys in the acid rain were lower than that in the air and deionized water.?3?The as-cast AlCoCrFeNi HEAs included a single fcc solid solution.AlN,CrN,and Fe₄N phases were observed on the surface of the nitrided alloys.The hardness values in the as-cast and nitrided HEAs were 522 HV and 720 HV,respectively.?4?The wear rate of the nitrided HEAs was lower than that of the as-cast HEAs in the same conditions.The lowest wear rate values of 7×10^-5 mm³/?N m?and 2.8×10^-5 mm³/?N m?for the as-cast and nitrided HEAs were obtained in the acid rain.The average friction coefficient of nitrided HEAs in the acid rain obtained a minimum of 0.213.?5?The presence of the oxidation film and nitrided layer prevented a direct contact between Si₃N₄ balls and the alloys,which reduced the wear rate.?6?The deionized water acted as lubricant during sliding,which decreased the abrasion of the surface.The corrosion of the acid rain accelerated the abrasion,and the major corrosion products were metal chloride.However,the lubrication action of the deionized water and acid rain led to the lower wear rate...