Ultrasonic Surface Modification of WC-Co-Cr Thermal Spray Coatings: Microstructure, Mechanical Properties and Performance

Thermal-sprayed WC–Co–Cr coatings are widely used to improve the wear and corrosion resistance of steel components operating under severe service conditions. This study investigates WC–Co–Cr coatings deposited by detonation spraying (DS), high-velocity oxy-fuel (HVOF), and atmospheric plasma spraying (APS) before and after ultrasonic nanocrystal surface modification (UNSM). The coatings were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS), together with microhardness, tribological, abrasive, erosive, impact-abrasive, cavitation, corrosion, oxidation, and valve endurance tests. The results demonstrate that the deposition technology strongly affects the coating structure and performance. UNSM produced a pronounced increase in microhardness, reaching 1468 HV for DS + UNSM, 1596 HV for HVOF + UNSM, and 1561 HV for APS + UNSM. Ultrasonic treatment also reduced material loss under abrasive, erosive, impact-abrasive, and cavitation conditions. APS + UNSM demonstrated the best performance in the principal laboratory wear tests, with the lowest abrasive mass loss (0.42–0.45 mg), erosive mass loss (0.55–0.60 mg), impact-abrasive mass loss (0.75–0.85 mg), and cavitation mass-loss rate (0.33–0.38 mg/h). In tribological testing, APS + UNSM exhibited the lowest coefficient of friction (0.28), compared with 0.32 for HVOF + UNSM and 0.36 for DS + UNSM. In valve endurance testing, HVOF + UNSM showed the lowest plunger displacement growth rate (0.050 mm/h) and the longest calculated time to reach the 2 mm displacement criterion (22 h). Overall, the combination of thermal spraying and UNSM improves the mechanical and service performance of WC–Co–Cr coatings, while the optimal coating condition depends on the specific degradation mechanism and operating conditions.