Development oTungsten Inert Gas and Microwave Treated Claddings In Improving Resistance to Wear at Elevated Temperatures

Abstract

The remanufacturing of high-value engineering components is becoming a mainstream practice to reduce the environmental impact. The components such as cams, gears, and bearings rely on the integrity of their interacting surfaces where loads act over a small surface area, leading to high contact stresses, which may further influence the grater region of the surface. Especially at elevated temperatures, components used in the aero engine, gas and steam turbines, and bearings lose their efficiency due to the deterioration of material properties. The components used in such adverse conditions are important to adapt suitable surface modification techniques to increase the service life. Cladding emerged as an effective surface modification technology and is widely used in many industries to protect the components against surface failures like wear, corrosion, and oxidation. Among many materials, titanium has numerous applications in a rocket motor, structural forgings and fasteners, pressure vessels, chemical gas pumps, marine components, and steam turbine blades, etc. Even though titanium alloy has a high specific strength and elevated melting temperature, it has low hardness and poor wear resistance. Hence the improvement of surface mechanical properties of titanium is essential to extend its application in an abrasive environment. The present work explores the TIG cladding technique and microwave hybrid heating (MHH) technique to enhance the surface properties of the titanium 31 alloy against wear at elevated temperatures. Commercially available materials such as NiCrSiB/WC, Ag, BaF2, MoS2, and hBN are used as the cladding powders. Four types of composite coatings were prepared, namely NiCrSiB/WC/Ag/BaF2, NiCrSiB/WC/Ag/hBN, NiCrSiB/WC/MoS2/BaF2, and NiCrSiB/WC/MoS2/hBN, and deposited on Titanium 31 grade alloy substrate by TIG cladding and microwave cladding techniques at optimized parameters. The claddings were characterized using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), Electron Backscatter Diffraction (EBSD), and X-ray diffraction (XRD). Further, claddings are characterized for microstructural and mechanical properties (porosity, dilution, microhardness, fracture toughness) and evaluated their potential for high temperature environments in sliding wear conditions. At optimized TIG and microwave hybrid techniques, less porosity (< 2%) and dilution were obtained. The influence of solid lubricants, namely Ag, BaF2, MoS2, and hBN, on NiCrSiB/WC claddings is dealt with for tribological performance at elevated temperatures. Dry sliding wear behavior of titanium 31 substrate, NiCrSiB/WC/Ag/BaF2, NiCrSiB/WC/Ag/hBN, NiCrSiB/WC/MoS2/BaF2, and NiCrSiB/WC/MoS2/hBN is evaluated using high temperature pin on disc tribometer. All four coatings showed a synergistic lubrication effect at low and high temperatures. Due to the reduction of surface contact against the alumina counter body, claddings displayed a lower friction coefficient and wear rate than the substrate. Based on the weight loss data, the relative wear resistance of the both TIG and microwave claddings under dry sliding conditions is arranged in the following sequence: NiCrSiB/WC/Ag/BaF2 > NiCrSiB/WC/Ag/hBN > NiCrSiB/WC/MoS2/hBN > NiCrSiB/WC/MoS2/BaF2. The combined lubricating effect of Ag and BaF2 solid lubricants incorporated in the claddings was adequate to reduce material loss than other composite claddings. Comparatively, TIG processed clads showed lower wear rates than the MHH clads at all wear testing conditions. Developed claddings in the present study exhibit higher temperature resistance than titanium 31 alloy substrate making them suitable for components subjected to elevated temperature service conditions.