Laser Cladding Surface Alloyed TC4

In this paper ,the structure, microhardness , friction resistence and the distribution characteristics of composition of laser clad zone of WC-12Co, 45C on TC4 were investigated. Cross-section of the laser clad zone showed three distinct regions which consisted of clad layer, melt zone and heat-affecting zone .The result showed that laser cladding leads to the formation of a continue and compact clad layer and the elimination of the lamallar structural character which occurred in plasma-spraying WC-12Co, 45C coatings. The difference in the composition, temperature and cooling speed in different areas of the coating leads to the result that there are several kinds of structural feathers including dendritic, polgon lumpish, petaloitic, lathy and particulate. The metallurgical combining interface between the cladding layer and matrix is achieved. The maximum of the microhardness of WC-12Co, 45C layers cladded by laser comes up to 1354 HV.The influence of laser power and coating thickness on the microhardness of the clad zone ,on the thickness of clad-layer and the depth of melt zone were studied using scanning electron microscope(SEM) and microhardness testing techniques. The result showed that given the WC-12Co coating thickness constant, the microhardness of clad zone increases while the depth of clad-layer decreases with the increment of laser power .The same is the case with 45C .The test of friction resistence of both kinds of clad-layers was conducted on GCr15 grinding wheel . The result showed that the friction resistence of WC-12Co clad-layer increased by 2 times or more compared with that of the corresponding plasma spraying coating , while the friction resistence of 45C clad-layer increased by 2.5 times compared with that of the corresponding plasma spraying coating . And the friction resistence of WC-12Co clad-layer is higher than that of 45C clad-layer . In addition , given the coating thickness constant , the friction resistence of both kinds of clad-layers increased with the increment of laser power .There is a process of convection at the bottom of the melting pond, where the alloy elements flows upwards, and the alloy element, Cr , Ni, Co etc. in coating layer, flows down. The effect of convection differs with the laser power. The alloy elements in the melting pond distribute more equably when the laser power is stronger.