Abstract
The effects of laser scanning speed on the microstructure, microhardness, and corrosion behavior of Ni45 coatings were investigated by using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness, and electrochemical measurements. The results showed that increasing laser scanning speed promotes the transformation from planar crystals to dendrites and refines the grains concurrently. The γ-(Ni, Fe), FeNi3, and M23(C,B)6 are identified as the primary phase composition in the Ni45 coatings regardless of the laser scanning speed. Thereinto, the formation and growth of M23(C,B)6 precipitates can be inhibited with increasing laser scanning speed due to the higher cooling rate, which affects the microhardness distribution and corrosion resistance of the coating. On the one hand, the microhardness of the whole coating presents a downtrend with increasing laser scanning speed due to the reduction of M23(C,B)6 phase. On the other hand, the corrosion resistance in 0.5 M NaCl solution is improved to some extent at higher laser scanning speed because the less precipitation of M23(C,B)6 reduces the depletion of Cr around the precipitates. In contrast, all the coatings exhibit undifferentiated but poor corrosion resistance in the highly corrosive 0.5 M NaCl + 0.5 M H2SO4 solution.
Highlights
Cladding technologies are usually employed to modify the surface structure and properties of alloys [1, 2], among which laser cladding exhibits some promising advantages [3,4,5]
All the interfaces were free of cracks and pores, indicating good bondings between the substrate and coatings. e thickness of the transition layer between the coating and heat-affected zone (HAZ) decreased with increasing laser scanning speed, which resulted from the hindered element diffusion between the coatings and substrate at a shorter heating time during the laser cladding process [8, 21, 22]
Ni45 coatings with good interface bonding have been prepared by the laser cladding process. e effects of laser scanning speed (4 mm/s, 6 mm/s, and 10 mm/s) on the microstructure, microhardness, and corrosion resistance of the as-prepared Ni45 coatings are clarified and explained: (1) e thickness of the transition layer between the coating and HAZ decreased the transformation from planar crystals to dendrites, and the grain refinements in the coatings were promoted. e formation and growth of M23(C,B)6 precipitates in the coatings were inhibited with increasing laser scanning speed due to lower thermal input and faster cooling rate
Summary
Cladding technologies are usually employed to modify the surface structure and properties of alloys [1, 2], among which laser cladding exhibits some promising advantages [3,4,5]. It is a simple, green, economic, and efficient process, which can make the surface coating have better corrosion resistance and wear resistance than the substrate [6, 7]. Fesharaki et al [14] reported better metallurgical bonding of Inconel 625 coating prepared by laser cladding than that developed by Tungsten Inert Gas Welding (TIG) cladding. Tanigawa et al [15] found that the HAZ of laser cladding prepared Ni-Cr-Si-B alloy coating on C45 carbon steel can be shrunken by employing smaller particles
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