Evolution of Microstructure and High-Temperature Tribological Performance of Self-Lubricating Nickel-Based Composite Tungsten Inert Gas Coatings

Abstract

The present study aims to assess the effect of Ag/BaF2 solid lubricant encapsulation in the nickel-based composite coatings for high-temperature tribological applications. The composite coatings (NiCrSiB/WC and NiCrSiB/WC/Ag/BaF<inf>2</inf>) have successfully been fabricated on the titanium 31 substrate by tungsten inert gas (TIG) cladding technique. The influence of the TIG processing current on the microstructure, microhardness, and fracture toughness was investigated. Mechanical characteristics of the coatings were further correlated with the microstructural morphologies. The coating fabricated at 70 A exhibited significantly higher hardness than other coatings. The tribological performances of the NiCrSiB/WC/Ag/BaF<inf>2</inf> composite coatings were superior to those of the NiCrSiB/WC coatings at both low (200 °C) and high (600 °C) temperatures. The synergistic lubrication effect of the Ag/BaF<inf>2</inf> solid lubricant combination provided lubrication at a wide range of temperatures. The addition of these solid lubricants in the nickel-based coating helped achieve the low coefficient of friction of 0.2 and lower wear rates. Particularly, oxide phases (such as NiO, TiO, Ni<inf>3</inf>Ti<inf>3</inf>O, and W<inf>3</inf>O) formed on the worn surface at 600 °C, and the lubricant phases (Ag, Ag<inf>2</inf>F, and Ba (TiO<inf>3</inf>)) provided excellent resistance to wear. © 2021, ASM International.