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Effects of Yttrium on the Microstructure and Wear Properties of Laser-aided Direct Metal Deposition (DMD) Co-285 + WC Coatings
R. Zhou, G-F. Sun, A-X. Feng, C-S. Liu, K. Wang, X-D. Ren and X-P. Bu

The laser-aided direct metal deposition (DMD) technique was used to form Co-285 + WC and Co-285+WC+Y coatings on 1018 mild steel. Microstructure, element distribution, phases, micro-hardness distribution and wear properties of the two coatings were investigated. Comparison indicates that both coatings were dense, and inhomogeneous with undissolved WC particles distributed in the Co-rich matrix. Microstructure around undissolved WC particles in Co-285 + WC coating exhibited gradient distribution, while that in Co-285+WC+Y coating has uniform distribution. Due to the addition of yttrium, no cracks were found in the latter coating while there were some micro-cracks in the former coating. Also, Co6W6C new phase and Cr7C3 instead of Cr3C2 were formed in Co- 285+WC+Y coating. The average micro-hardness of the matrix in Co-285 + WC coating was 751 HV0.5, which was almost 1.2 times that of Co- 285+WC+Y coating (632 HV0.5). Wear results at ambient room temperature indicated that wear resistance of the two coatings was almost the same (Co-285+WC+Y coating was 1.06 times that of Co-285+WC coating) after 420 m (60 minutes) sliding wear test. Addition of yttrium did not change the wear mechanism. Effects of yttrium on the microstructure, phases and wear resistance were discussed.

Keywords: CO2 laser, yttrium, cobalt, tungsten carbide, laser-aided direct metal deposition (DMD), microstructure, sliding wear resistance

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