Preparation of Wear-Resistant Coating on Ti6Al4V Alloy by Cold Spraying and Plasma Electrolytic Oxidation

In order to improve the wear resistance of Ti6Al4V alloy, the alloy was first coated with alumina-reinforced aluminum coating (CS-coating) by cold spraying, and then the alloy with CS-coating was processed by plasma electrolytic oxidation (PEO) under unipolar mode and soft sparking mode, respectively, to prepare wear-resistant PEO coatings. For comparison, Ti6Al4V alloy without CS-coating was also subjected to PEO treatment. The microstructure, phase composition, hardness, and wear resistance of the PEO coatings formed on Ti6Al4V alloy with and without CS-coating were investigated. The results revealed that PEO coatings formed on Ti6Al4V alloy with CS-coating under soft sparking mode contained more α-Al2O3, possessed larger thickness, more compact microstructure, and higher microhardness than that formed under unipolar mode. The PEO coating formed on Ti6Al4V substrate was mainly composed of TiO2 and had pores and cracks. Among all these coatings, PEO coating formed on Ti6Al4V alloy with CS-coating under soft sparking mode exhibited the best wear resistance with a wear rate of 1.18 × 10−5 mm3/(Nm), which was only 15.28% of that of the Ti6Al4V substrate. The investigation indicated that the combination of cold spraying and PEO under soft sparking mode is a promising technique for improving the wear resistance of titanium alloy.

Laser Metal Deposition of an AlCoCrFeNiTi0.5 High-Entropy Alloy Coating on a Ti6Al4V Substrate: Microstructure and Oxidation Behavior

Ti6Al4V has been recognized as an attractive material, due to its combination of low density and favorable mechanical properties. However, its insufficient oxidation resistance has limited the high-temperature application. In this work, an AlCoCrFeNiTi0.5 high-entropy alloy (HEA) coating was fabricated on a Ti6Al4V substrate using laser metal deposition (LMD). The microstructure and isothermal oxidation behaviors were investigated. The microstructure of as-deposited HEA exhibited a Fe, Cr-rich A2 phase and an Al, Ni, Ti-enriched B2 phase. Its hardness was approximately 2.1 times higher than that of the substrate. The oxidation testing at 700 °C and 800 °C suggested that the HEA coating has better oxidation resistance than the Ti6Al4V substrate. The oxide scales of the Ti6Al4V substrate were mainly composed of TiO2, while continuous Al2O3 and Cr2O3 were formed in the HEA coatings and could be attributed to oxidation resistance improvement. This work provides an approach to mitigate the oxidation resistance of Ti6Al4V and explore the applicability of the HEA in a high-temperature environment.