In Situ Titanium Carbide Deposition on Aluminum Using Electrical Discharge Coating Process With Ti6Al4V Tool

Abstract Surface coating is a crucial tool to enhance the wear resistance, hardness, and overall longevity of vital components across diverse industries such as automotive, aerospace, and marine. Al6061 alloy is widely utilized in these industries for its strength, lightweight, and corrosion resistance; however, it is susceptible to wear and saltwater corrosion. This is typically addressed by surface modification or coatings to enhance hardness, thermal stability, and corrosion resistance to enable high-performance applications of the alloy. This paper investigates the efficacy of Ti6Al4V alloy in depositing in situ titanium carbide coatings onto the Al6061 substrate using the electrical discharge coating (EDC) method. Unlike other surface coating methods, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and laser cladding, EDC uses a simpler setup, operates under ambient conditions, and is a cheaper solution. EDC experiments are conducted via Ti6Al4V AM tools produced via direct metal laser sintering (DMLS), with Al6061 as the substrate and a hydrocarbon-based oil as the dielectric medium. The experiments are designed by varying two key process parameters that affect discharge energy, i.e., current and open gap voltage, at two levels each while keeping other parameters such as pulse-on time, pulse-off time, dielectric fluid, and coating time constant. The resulting coating thickness was measured over a length of about 2500 μm at an equal interval of 20 μm to observe spatial uniformity. As the current increases, the average coating thickness increases from 24 μm to 35 μm due to higher discharge energy leading to greater deposition from tool material. Whereas, no clear trend in coating thickness is observed with an increase in the open gap voltage. Energy dispersive x-ray spectroscopy (EDS) field mapping of the surface is used to confirm the presence of titanium (Ti), aluminum (Al), and vanadium (V) in the deposition. Cross-sectional line-EDS analysis is conducted to reveal elemental variation from the top edge to the substrate, affirming titanium deposition throughout the coating depth. X-ray diffraction (XRD) results confirmed the presence of titanium carbide in the coating region. As a result, the surface microhardness of the coated sample is shown to double when compared to that of the bare Al6061 substrate. It is, however, observed that the deposition is non-uniform across the surface of the Al6061 substrate, depicting the need for better process control.