Abstract
Ni60B coating and Cr3C2-NiCr coating were prepared through the plasma spraying technology on steel roll substrate surface in this paper. Optimized the spraying process parameters, used tensile test, hardness test and thermal shock test with other related equipments or instruments, and had a research of coating structure and property.As the index of the combination strength of coating and substrate, by the orthogonal experiment method, optimized the main parameters of spraying --namely spraying distance,the main steam flow, the sending powder amount and spraying power, and analyzed the every parameter influence law on the coating structure and properties. Observed the fracture tensile test, fracture mainly happened in coating and substrate. The coating under the optimization parameters, its bonding strength was greater than the group before optimization samples strength. Ni60B coating binding strength after optimization was 59.311MPa, Cr3C2-NiCr coating binding strength after optimization was 68.491MPa,realized the optimization effect.
Prepared the metallographic specimen of coating, to observe the microstructure observation, the coatings are characteristic of lamellar microstructure and porosities, micro cracks. The coalescent between coating and substrate is most of mechanical bond. The optimized coating organization, the number of pore, crack defects reduced significantly.XRD analysis showed that the before and after spraying, coating material did not appear obvious phase change, had kept the original powder characteristics，such as high hardness etc. Coating's micro hardness of parallel to the matrix and perpendicular to the direction of the matrix, coating micro hardness was dispersion, but accorded with normal distribution significantly.
The thermal shock test of Ni60B coating and Cr3C2-NiCr coating, it found that two coating both had a good thermal shock performance, a high fever fatigue life. The thermal shock temperature were selected as 650℃ and 450℃, after the thermal shock test, found that the higher thermal shock temperature, the thermal fatigue life was short; Conversely,life was long. The main failure forms of the coating were the cracks of the coating initiate, expanded and then overall peel from the interface along the coating and substrate, and the failure of small pieces off. The thermal temperature had a larger influence of thermal shock failure forms.
Keywords: steel roll; plasma spraying; orthogonal experiment; bonding strength; thermal shock test
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