Effects of B4C particle size and content on microstructure and properties of in-situ TiB2-TiC composite coatings prepared by plasma spraying

Abstract

In order to improve the surface properties of titanium alloy, in-situ TiB2-TiC composite coatings were successfully prepared by plasma spraying Ti-B4C composite powder. The effects of particle size and content of B4C raw powders on the phase composition, microstructure, and mechanical properties of the TiB2-TiC coatings were systematically evaluated. The results reveal that the decrease of B4C particle size had a significant effect on the increase of hard phases (TiB2 and TiC) in the 3Ti-B4C (1 μm) composite coating. Meanwhile, the density of the 3Ti-B4C (1 μm) coating was increased with the decrease of B4C particle size, so the microhardness of the 3Ti-B4C (1 μm) coating was significantly better than that of the 3Ti-B4C (19 μm) coating. The reduction of B4C (1 μm) content (Ti:B4C = 5: 1, 7: 1 and 9: 1) in the composite powders could promote the reaction of the system to form new phase TiB, and the main phases of the 5Ti-B4C, 7Ti-B4C and 9Ti-B4C coatings was finally transformed into TiC, TiB2 and TiB. The hardness of the composite coatings was improved with increasing of Ti: B4C from 3: 1 to 5: 1, but the hardness of the samples obtained by spraying 7Ti: B4C and 9Ti: B4C composite powders were drastically decreased. What's more, the 5Ti-B4C (1 μm) composite coating possessed good toughness. The toughening mechanism was mainly attributed to the grain refinement, dispersion strengthening and microstructure densification.