| In order to obtain wear-resistant coatings with good properties, a laser cladding of GH 864 nickel based superalloy substrate with Ni75Si25, Ni75Si25-B, Ni75Si25-Nb, Ni78Sil3Ti9, Ni78Sil3Ti9-WC, Ni78Sil3Ti9-(Ti+C) powder was performed. The microstructure of clad layers was characterized using XRD, SEM and EDAX. The microhardness of clad layers was measured using HVS-1000 type microhardness tester. Through the comparison analyses of macroscopic and microscopic quality for the above laser clad layers, the Ni78Sil3Ti9-(Ti+C) pre-alloyed powder was chosen as optimal clad materials.Under the optimized cladding parameters, the Ni78Sil3Ti9-(Ti+C) clad layers without of pores and cracks can be obtained, and an excellent bonding between the clad layer and the substrate was ensued by a strong metallurgical interface. The microstructure of the coating was mainly composed of Y -Ni, Ni3(Si,Ti) and TiC, which means that the TiC particles can be in-situ formed. From interface to the coating surface, the TiC not only presented a variety of steps on the quantity, and the size of TiC particles but also enlarged gradually, which was advantageous to exalt the strength and wear resistance of coatings. The mechanism of TiC formation regarded the dissolve-crystal mechanism as principle.The microhardness distribution curve of the Ni78Sil3Ti9-(Ti+C) clad layers was composed of three parts: the clad layer, the heat-affected zone and the substrate. The microhardness of clad layers was the tallest, the heat-affected zone was middle, and the microhardness of substrate was the lowest. With the increasing of (Ti+C) addition, the hardness of coatings was going up one by on in order, when the content of (Ti+C) attains 20 wt%, the hardness of coating can reach Hv780 that was 2.4 times of the substrate, and the hardness distribution was also very even. The coatings had a high hardness distribution because of the rapidly solidified fine microstructure and the presence of TiC reinforcement. |
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