Impact Wear Behavior of NiCr-Cr₃C₂ Coatings with Different NiCr Contents at High Temperature

Steam turbine is a kind of power machinery that converts the heat energy generated by fuel combustion into mechanical energy for driving power generation, and is the key equipment of coal power units, nuclear power units, gas and steam cycle generating units and other units. In the actual work of the steam turbine, due to the influence of high temperature, high pressure steam, high pressure fluid, etc., the key components of the steam turbine are susceptible to corrosion, mechanical damage, impact wear and other problems. In order to extend the service life of these components, a protective coating is usually applied on the surface of the components by various processes. NiCr-Cr₃C₂ coating prepared by thermal spraying technology has excellent high temperature wear resistance and corrosion resistance, and has the potential to serve as a protective coating for turbine components. At present, there have been many studies on the properties of NiCr-Cr₃C₂ coating, but there are few reports on the impact wear behavior of this coating under high temperature environment. In this paper, 35% NiCr-Cr₃C₂ coating and 25% NiCr-Cr₃C₂ coating with different NiCr content were prepared by supersonic flame spraying. The real service condition of steam turbine was simulated by using a self-developed high-temperature iron chip impact wear tester. Impact tests (1×10⁴, 2×10⁴ and 5×10⁴) were carried out at 630 ℃ and under the environment of iron filings erosion. The impact wear behavior of the two coatings under the environment of iron filings erosion at high temperature was studied through the dynamic response during impact and the wear pattern after impact. The dynamic response data in the impact process mainly included the impact velocity curve and the impact force curve, which were collected by the corresponding sensor. The macroscopic morphology of the wear marks was observed by ultra depth of field optical microscope, and the microscopic morphology of the surface and cross section of the wear marks was observed by scanning electron microscope. The maximum wear depth and wear area and volume of the wear mark were obtained by measuring the contour of the wear mark with white light interferometer. The distribution of elements on the surface and cross section of the abrasion were analyzed by energy dispersive spectrometer. The results showed that the damage mechanisms of 35% NiCr-Cr₃C₂ coating and 25% NiCr-Cr₃C₂ coating were plastic deformation and abrasive wear, and the wear areas of the two coatings were not different under the same impact times. With the increase of impact times, the impact energy, energy absorption rate and wear area of the two coatings all showed an increasing trend, while the peak value of impact force showed a decreasing trend, that was, with the increase of impact times, more material removal and plastic deformation occurred in the two coatings. The wear volume of 25% NiCr-Cr₃C₂ coating increased with the increase of impact times, and under the same impact times, the energy absorption amount, absorption rate and wear volume of 25% NiCr-Cr₃C₂ coating were smaller than that of 35% NiCr-Cr₃C₂ coating, showing better resistance to high temperature impact wear. In the high temperature environment, the iron filings had good durability and were easy to be compacting by the impact ball and became the third body between the impact ball and the impact sample. As the formation of this third body would fill part of the pits on the wear marks, the wear volume of 35% NiCr-Cr₃C₂ coating would first increase and then decrease with the increase of impact times.