Applying resistant coatings by surface modification techniques are widely used to improve the wear, erosion and corrosion resistance and hardness of the metallic components. NiCrBSi alloy is one of the most widely used Nickel-based alloys with desirable properties for wear and erosion applications. In this study, characterization of NiCrBSi, NiCrBSi-30%WC and NiCrBSi-60%WC coatings, fabricated by laser coating process, was performed. Microstructural investigations and phase transformation studies of coatings were carried out using X-Ray Diffraction (XRD) test, Optical microscope (OM) and Scanning Electron Microscope (SEM) equipped with X-ray Energy Dispersive Spectroscopy. The XRD results indicated that NiCrBSi coating mostly consisted of γ-Ni phase with FCC crystal structure and Ni3B and CrB boride phases. In composite coatings, however, Cr7C3, Cr23C6, WC and W2C carbide phases were also found in addition to the above-mentioned phases. The microscopic investigations showed that while some cracks were formed in the NiCrBSi coating in the direction perpendicular to the scanning direction of the laser beam on the surface of the coating, in NiCrBSi/WC composite coatings, these cracks were observed. The matrix of NiCrBSi coating consisted of dendritic and inter-dendritic microstructure. In composite coatings, partial melting of WC particles during the laser coating process led to the formation of diffusion zone as well as the precipitation of needle-shaped and blocky carbides near these particles. The microhardness measurement results from the cross section of the coatings showed that the microhardness of the coatings increases by addition of WC reinforcing particles which can be due to the distribution of WC hard phase, its partial dissolution and the formation of hard secondary phases. Additionally, by increasing the amounts of reinforcing particles from 30 to 60%, hardness of coatings significantly increased. The erosion, wear and corrosion resistance of the coatings were also eva‎luated. The results of tribological investigations indicated that the addition of reinforcing particles improves the erosion and wear resistance of coatings. The erosion test results showed that the erosion resistance of NiCrBSi coating at the angle of 90 degree was high whilst a suitable erosion behavior was observed in NiCrBSi/WC composite coatings at the angle of 30 degree. NiCrBSi-30%WC composite coating had the best wear and erosion resistance. By increasing WC content to 60%WC, a significant effect on wear and erosion was not observed. In NiCrBSi coating, erosion occurred with a ductile mechanism. In contrast, the erosion mechanism in composite coatings was brittle. The dominant wear mechanism in NiCrBSi and NiCrBSi-30%WC coatings was delamination and oxide mechanism while in NiCrBSi-60%WC coating, wear mainly occurred with an adhesive mechanism. The results of corrosion tests indicated that addition of WC reinforcing particles and increasing the volume fraction of WC led to a reduction in the corrosion resistance of coatings.

عبدالمجيد اسلامي , فخرالدين اشرفي زاده

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قاسم عظيمي روئين , ابوذر طاهري زاده