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Study On Microstructure And Properties Of Co-base Coating Prepared By Plasma Spray

Posted on:2011-05-26Degree:MasterType:Thesis
Country:ChinaCandidate:P R ChenFull Text:PDF
GTID:2121330338480443Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
The powder of cobalt-based self-fluxing alloy has been widely used in wear-resistant coating because of the excellent performance such as heat resistance, corrosion resistance, wear resistance, high temperature oxidation resistance and so on. Plasma spraying has been widely used to make coating because operation is simple, efficiency of spraying is high and the thickness of the coating is controllable. In this article the Co-base coating and Co-base compound coating containing different proportions of WC were prepared by using plasma spraying in order to improve surface properties of 12Cr1MoV and reduce cost. Then remelting treatment was adopted. The organization and properties were investigated before and after remelting treatment.The powder of cobalt-based self-fluxing alloy was refined by Mixing Mill for 10h. The phases were stillγ-Co and Cr23C6.However, the size of powder was significantly refined from 200μm to 70μm. The Co-base coating was prepared at different spraying currents. It was discovered that the value of porosity was the minimum and phases did not change at 500A. The combination between coating and substrate was mechanical. Results of the measurement revealed that the hardness value of Co-base coating was 447.8HV and the friction coefficient was stably kept at 0.42. The wear scars were shallow on the surface. The corrosion potential of Co-base coating was -583mv. The corrosion current density was lower when spraying current was 500A. The Co-base coating has better performance when the spraying current was 500A.Different proportions of WC (10wt%,15wt%,20wt%) were added in Co-base alloy powder. The organization of compound coating at 500A was investigated. It was found that the porosity increased with the proportions of WC rising and WC has been decomposed to W2C at high temperature. By interface analysis, the combination between coating and substrate was mechanical. Study on microhardness and wear resistance of the coating, the hardness value of 20%WC compound was 715.2HV, however the friction coefficient was unstable. The hardness value of 15%WC compound coating was 664.5HV and the friction coefficient was about 0.40. After corrosion resistance testing, the corrosion potential of 15%WC compound coating was found to be -576mv, passivation current density was lower (1.57×10-8A/cm2). The 15%WC compound coating has better performance than others.Some elements were diffused between interface of coating and substrate after remelting treatment at 1050-1150℃. Co3B and Co6W6C were added into Co-base coating and Co2C and Co6W6C were added into compound coating after remelting treatment. With the increase of temperature, the porosity significantly reduced, the organization was becoming uniform and element diffusion was much more obvious than before. The layer structure of the coating disappear, particles have been fusion and bonding strength of coating noticeably improved at 1150℃. The hardness of Co-base coating and compound coating were slightly decreased after remelting treatment. The highest hardness value of Co-base coating appeared at 1100℃, but the coefficient friction was increased after few minutes. The corrosion potential of Co-base coating was -480mv and the region of passivation reached about 455mv at 1100℃. The compound coating has the highest hardness (621HV) at 1150℃and coefficient friction was stable at 0.33. The corrosion potential of compound coating did not change a lot, but the region of passivation reached about 500mv at 1150℃.
Keywords/Search Tags:plasma spraying, Co-based alloy, microstructure, wear resistance, corrosion resistance
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