| Solid particle erosion (S.P.E) is one of important failure forms of turbine blades. The plating treatment on the surface of turbine blades is a primary means to improve the erosion resistance. Surface modification treatment on the 2CrlOMoVNbN steel was conducted using multi-arc ion plating method. The microstructure of CrNx coating was analyzed and the study was focused on the S.P.E. resistance of both coating and base metal. The experimental results are as follows:it was successively composed of CrN+Cr2N+Cr, Cr2N+Cr, and Cr2N+Cr+Fe-Cr(solid solution) phases from coating surface to interface of film-substrate. The microstructure was dense with raised droplets on the surface and fewer defects in the coating. There were elementary substance Cr particles in the coating. The bonding state of coating-substrate was good.2Cr10MoVNbN substrate steel was characterized of typical wear characteristics of plastic materials, and the erosion wear rate was maximum at the impacting angle of about 22°. The CrNx coating was characterized of typical wear characteristics of brittle materials, and the erosion wear rate was maximum at the impacting angle of 90°. The bigger the impacting velocity, the greater the erosion wear rate. The erosion wear mechanism of two tested materials was determined (obtained) by means of ANSYS/LS-DYNA finite element simulation (FES) and morphology analysis on the material surface which was afer erosion wear. For the 2Cr10MoVNbN steel, the morphologies of "plough " and "deformed lip" were as the main failure characteristics at low-angle, the deformed lips were directly sheared out due to higher energy effect of erodents, which was composed of 75% sheets with higher velocity, showing serious erosion wear. Under the condition of high-angle, the failure was mainly characterized of plastic deformation, and the ability of plastic deformation was dissipated due to the repeated impacts of erodents, and resulted in surface fatigue spalling. At low-angle, there were still traces of slight cutting in the CrNx coatings because of the factors such as microstructure with fewer defects. There were the removals of pieces (flakes) and the pull out of Cr droplets in the positions of defects and shedding Cr droplets. At the high-angle, the erodents impacted the coating surface and resulted in local stress concentration, which easily propagated along the inter-plates and made the cracks connected together under the repeated impacts of erodents, leading to pieces spalling. Through making a comparison between the S.P.E. resistances of the base metal and CrNx coating, it was found that the S.P.E. resistance of CrNx coating was much superior to that of the substrate as the high-temperature. When the impacting velocity was 210m/s, the erosion wear rate of substrate was 400 times of CrNx coating at the impacting angle of 18°and it was about 27 times at 90°; When the impacting velocity was 420m/s, the erosive wear rate of substrate was 400 times of CrNx coating and it was about 3 times at 90°. Meanwhile, making a comparison between boriding layer(which was regularly used as protective coating of steam turbine) and CrNx coating on the two aspects of experimental results of erosion wear and fracture toughness, it was found that whether at the impacting angle of 18°or 90°, the erosion wear rate of boriding layer was much higher than that of CrNx coating, that is to say, the plated CrNx coating showed better erosion resistance than the boriding layer. The fracture toughness of CrNx coating was superior to boriding layer but the hardness was close to each other. Thus, it is concluded that CrNx coating was an ideal protective coating of the steam turbine blade to S.P.E.. |
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