Elevated temperature erosion of HVOF Cr 3C 2/TiC–NiCrMo cermet coating

Abstract

The high-velocity oxygen-fuel (HVOF) coating from composite Cr 3C 2/TiC–NiCrMo powder is used for protection of steel components against elevated temperature erosion in energy conversion and utilization systems. The paper presents results of this coating protective properties investigation, using a nozzle type elevated temperature erosion tester. The influence of the test temperature, particle erosivity, velocity and impact angle on the material wastage was revealed. The elevated temperature erosion behavior of this coating was compared with that of 1018 low carbon steel, and other thermal sprayed coatings including HVOF Cr 3C 2–NiCr, HVOF WC–Co cermet coatings, an arc-sprayed Fe–Cr–Si–B coating and a low velocity flame-sprayed Cr 2O 3 ceramic coating. The hardness, bond strength and thermal shock resistance of the coatings were measured. The morphology and structure of specimens were examined by optical and scanning electron microscopy. It was found that the Cr 3C 2/TiC–NiCrMo coating exhibited excellent thermal shock resistance and high erosion resistance at both shallow and steep impact angles, with 2–3 times less thickness loss than the Cr 3C 2–NiCr coating and the same level of erosion resistance as the WC–Co coating. The elevated temperature erosion wastage of the Cr 3C 2/TiC–NiCrMo coating tested at a 30° impact angle increased with particle velocity according to a power law having a velocity exponent of 3.11, which is slightly higher than that of the Cr 3C 2–NiCr coating. Tested at a 90° impact angle and at higher velocities, especially using a high erosive erodent, the Cr 3C 2/TiC–NiCrMo coating showed strong brittle erosion behavior with very high erosion wastage. The erosion behavior of this coating was found sensitive to the test temperature. Thus, this coating is not suitable for application over 600°C during service.