Wear and Corrosion of HVAF and HVOF-Sprayed WC-CoCr Coatings on Aluminum Alloy

Abstract

Light alloys are being increasingly investigated as alternatives to ferrous-based engineering components, based on weight considerations. However, in-service applications of such light alloy components often require a surface modification step to enhance their wear and corrosion responses for improved functionality. Thermally sprayed cermet coatings offer an enhanced resistance to wear and corrosion. This work investigates WC-CoCr coatings deposited using two different feedstocks comprising fine and coarse powder size distributions on aluminum alloy and steel substrates using high-velocity air-fuel (HVAF) and high-velocity oxy-fuel (HVOF) spray techniques. The WC-CoCr coatings were HVAF sprayed at various parameters to investigate the relationship between the processing conditions, microstructure, and performance. Microindentation, dry sliding wear, dry sand abrasion, cavitation erosion, and corrosion tests were conducted to assess the performance of the coatings. Despite the qualitative similarities in the microstructures of the coatings, the measured microindentation hardness values were observed to vary, and coatings deposited with higher particle impact velocities showed the highest microhardness between 1400 and 1600 HV0.3. For the three categories of wear investigated, the HVAF coatings showed better resistance than the HVOF coating investigated in this study. The estimated average specific wear rate (SWR) due to sliding wear of the HVOF coating was ~ 16.7 ± 4.0 × 10⁻⁸ mm³/Nm compared to that of the most resistant HVAF coating, which exhibited a SWR of ~ 1.7 ± 0.6 × 10⁻⁸ mm³/Nm. The cumulative mass loss rate due to the abrasive wear on the HVOF coating reached ~ 1.11 mg/min compared to ~ 0.76 mg/min of the most abrasion-resistant HVAF coating. All coatings showed similar corrosion resistances under the investigated conditions. The combination of wear and corrosion performance of the respective coatings could provide insight into the coating selection for intended applications.