ABSTRACT
Laser cladded Ni-based alloy coating reinforced by WC particles has broad application due to its excellent wear-resistant property. But because of many differences of the property between Ni-based alloy and WC particle,WC particles incline to deposit on the interface, which is apt to bring on stress concentration and form crack. If the Ni-based alloy gradient coating reinforced by WC particles in which the content of WC distributes gradiently from surface to interface is produced, it will relax the thermal stress greatly so that to eliminate the crack of coating and gain excellent mechanical property.
This article is about producing Ni-based alloy gradient coatings reinforced by WC particles through multilayer laser cladding. The main content is to optimize laser cladding technics to gain the good formation of coating, eliminate the crack of coating through preheating, analyze the microstructure of coating, test the mechanical property of coating and finally produce Ni-based alloy gradient coating reinforced by WC particles with excellent property.
The result of the research goes as follows. In the process of single track laser cladding Ni-based WC composite coatings, with the increasing content of WC particles, the dilution rate of cladding layer increases, γ- Ni dendrites in the top of cladding layers first coarsen then refine, and dendrites in the bottom of cladding layers coarsen steadily. In the single track laser cladding layers with different WC content, WC particles dissolve and react with surrounding elements to form different carbides, which exist in the shape of branch, block and grain. The average hardness of cladding layers increases with the adding of WC. When the weight percent of WC increases to 30%,the hardness of cladding layers is four point three times of the substrate. It can get good cladding effect through preheating the substrate under 350 ℃.Compared with no preheating, the crack of Deloro60 overlap cladding layer can be eliminated completely and the reduction of cladding layer hardness is little under 350 ℃ preheating, so it is a good base of gradient coating. The phase of gradient coating produced based on Deloro60 overlap coating mainly contains γ-Ni branch, eutectic included γ-Ni、Ni3B、Ni3Si and dispersed hard phase included M6C、M23C6、M7C3、CrB and so on. With the increasing of WC content in the gradient coating, there are more hard phases whose kinds are also different because of the dissolution of WC, and the quantity of γ-Ni dendrites decrease. The microhardness of Ni/WC gradient coating increases continuously from interface to the surface, and the highest hardness of surface can reach 1400 HV, which is about eight times of the substrate. The microhardness of every inferior layer are higher than the single track cladding layer with the same component. The average microhardness of gradient coating is about 960 HV, which is about five point six times of the substrate. The wear testing shows that the wear-resistant property of Ni/WC gradient coating is about three point eight times of the CCS-B substrate, which shows excellent wear- resistant property of Ni/WC gradient coating.
KEY WORDS: laser cladding, gradient coating, Ni-based alloy, WC
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