Microstructure and High-Temperature Properties of Cr3C2-25NiCr Nanoceramic Coatings Prepared by HVAF

Abstract

The study examines the microstructure and high-temperature properties of Cr3C2-25NiCr nanoceramic coatings on 316H high-temperature-resistant stainless steel that were prepared by high-velocity air–fuel spraying (HVAF) technology. The micromorphology, phase composition, fracture toughness, high-temperature hardness, high-temperature friction, and wear properties of the coating were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), high-temperature Vickers hardness tester, high-temperature friction and wear tester, and surface profiler. The results show that the Cr3C2-25NiCr coating prepared by HVAF presents a typical thermal spraying coating structure, with a dense structure and a porosity of only 0.34%. The coating consists of a Cr3C2 hard phase, a NiCr bonding phase, and a small amount of Cr7C3 phase; The average microhardness of the coating at room temperature is 998.8 HV0.3, which is about five times higher than that of 316H substrate. The Weibull distribution of the coating is unimodal, showing stable mechanical properties. The average microhardness values of the coating at 450 °C, 550 °C, 650 °C, and 750 °C are 840 HV0.3, 811 HV0.3, 729 HV0.3, and 696 HV0.3 respectively. The average friction coefficient of the Cr3C2-25NiCr coating initially decreases and then increases with temperature. During high-temperature friction and wear, a dark gray oxide film forms on the coating surface. The formation speed of the oxide film accelerates with increasing temperature, shortening the running-in period of the coating. The oxide film acts as a lubricant, reducing the friction coefficient of the coating. The Cr3C2-25NiCr coating exhibits exceptional high-temperature friction and wear resistance, primarily through oxidative wear. The Cr3C2-25NiCr coating exhibits outstanding high-temperature friction and wear resistance, with oxidative wear being the primary wear mechanism at elevated temperatures.