Effects Of Ultrasonic Vibration On Laser Cladding Ni60B And Wc/Ni60B Coatings

Laser cladding is a kind of high energy density surface treatment technology, it has many advantages which other surface treatment methods cannot compare with. Ni-based self-fluxing alloy powder has excellent properties, such as corrosion resistance, anti-oxidation, wear resistance. Ultrasonic has good refine effect on metal solidification. The influence of ultrasonic to laser cladding Ni60B and WC/Ni60B coatings were researched in this paper. The microstructure, crack, micro-hardness and wear resistance were systematically analyzed by scanning electron microscope with energy disperse spectroscopy, X-ray diffractomer, micro-hardness test system and multi-function surface compositive test instrument. Research results and main conclusions were summarized as follow:(1) In this study, the influence degree of main laser cladding processing parameters to the laser cladding coating and crack were ranked as follow:scanning velocity>current and impulse width (namely laser power)>powder feeding velocity>frequency.(2) With the aid of ultrasonic, the Ni60B laser cladding coating microstructure got well-distributed and fine, dentrite reduced and isometric crystal increased. In the Ni60B+10%WC coating, WC dissolved mostly and ultrasonic vibration improved the WC distribution in the whole coating and the microstructure became fine. Fully dissolved WC was found at the bottom of the Ni60B+20%WC coating, and there were more dissolved WC re-precipitation in the middle of the coating. WC particles aggregation was weakened by ultrasonic vibration. The WC distribution character which was concentrated in the middle and at the top of the coating kept the laser cladding coating with high hardness and excellent wear resistance, meanwhile ensured the metallurgical bonding with the substrate. Ultrasonic had a great influence to the microstructure of laser cladding Ni60B+10%WC coating.(3) There were many transverse cracks which were perpendicular to the direction of laser scanning speed in the Ni60B coating. Cracks on the upper layer of the coating were mainly cold cracks, and cracks propagated throughout the cross-section of the coating were mainly hot cracks. After adding ultrasonic vibration, the cracks reduced, but there were still several micro-cracks. Crack-free and good qualified laser cladding Ni60B coating by adding1%Y2O3was obtained with the aid of ultrasonic. In the WC/Ni60B coating, there were many transverse and longitudinal macro micro cracks. The crack number and crack gap in extent obviously decreased after ultrasonic vibration, meanwhile ultrasonic had a prominent effect to the crack inhibition of the Ni60B+20%WC coating.(4) The micro-hardness of the laser cladding Ni60B+1%Y2O3coating was HOOHVo.2, and the surface layer micro-hardness of the laser cladding Ni60B+10%WC coating could reached1750HV0.2both with the aid of ultrasonic.(5) The micro-hardness of the laser cladding Ni60B coating and WC/Ni60B coating without the aid of ultrasonic fluctuated violently, the homogenization and numerical value were improved after ultrasonic vibration.(6) Wear resistance of the laser cladding Ni60B and WC/Ni60B coating were improved with the aid of ultrasonic vibration, and the stability of the friction coefficients got better. To the laser cladding Ni60B coating, the wear mechanism was endurance failure and abrasive wear compared with endurance failure to the laser cladding WC/Ni60B coating. The laser cladding Ni60B+10%WC coating with the aid of ultrasonic had the best wear resistance and the smallest friction coefficient compared with other coatincs.