Study On The Mechanism And Law Of Rolling/sliding Competing Failure Of NiCrBSi Coatings Prepared By Plasma Spraying

Plasma spraying, widely used in surface modification, is a technique to prepare coatings with good performance by using plasma arc as its heat source, which could acquire flame flow with high-temperature and high droplet flight speed. Ni-based coatings prepared by plasma spraying are in good wear resistance and fatigue resistance, which could effectively improve the service life of the workpiece. Plasma sprayed coatings served in actual conditions are usually in a rolling/sliding coexistence contact state, and fail in a wear-andcontact-fatigue coexisting mode.In this paper, NiCrBSi alloy coatings were deposited by high-efficiency supersonic plasma spraying technology(SPS) and conventional air plasma spraying technology(APS). The optimal spray parameters of depositing SPS NiCrBSi alloy coatings, such as spraying distance, spraying current, spraying voltage and argon flow, were analyzed and determined by adopting the orthogonal experiment. The microstructure, porosity, phase composition, and micro-hardness of SPS coatings were respectively experimented, analyzed and compared with APS coatings by lots of equipments and methods, by XRD, SEM, etc. Ni-based alloy coatings deposited by supersonic plasma spraying and conventional air plasma spraying technology had been systematically tested in its rolling contact fatigue stress state and concluded in their different failure behavior and evolution of life. To study the Ni-base alloy coating failure mechanisms and laws of varying contact state, a software that could provide random slip ratio had been developed. Finally the results showed that:(1) Spraying parameters have significant impact on coating performance when supersonic plasma spraying NiCrBSi coatings. The orthogonal test showed the order of importance of spray parameters affecting the quality of the coating is: sprayin voltage> Ar flow> spraying distance> spraying current.(2) It had been found that in pure rolling contact state, contact stress significantly affect coating NiCrBSi contact fatigue failure mechanisms. High contact stress reduces contact fatigue life of the coating, and will increase the probability of occurrence of delamination failure.(3) Under the same contact stress, APS coatings have lower service life, due to their high porosity and low bond strength. The occurrence probability of delamination failure of APS coatings is greater than that of SPS coatings.(4) The slip ratio affects the service life and failure mechanism of the prasma sprayed coatings. When tested by the software and relating testing machines, coatings with changing slip ratio over time serve a shorter time than that of constant slip ratio.