Study On Laser Cladding Process And Properties Of Co Based Alloy

The Co based alloy cladding layer and with 10%WC cobalt based alloy cladding layer were successfully obtained by a combination of the fiber laser and simultaneous powder-feeding technology. The influence of scanning speed, overlapping ratio, substrate preheating and WC on the structure and properties of cladding layer were studied. The microstructure, composition distribution and phase composition of the cladding layer were analyzed by scanning electron microscope, energy spectrum analyzer and X-ray diffraction technique. The microhardness and macrohardness of cladding layer were analyzed by hardness test. The tensile compressive property and wear resistance of the cladding layer were studied by tensile compression test and friction and wear experiment.The experimental results show that the metallurgical bonding between the cobalt base alloy powder and the matrix is good. In the transverse melting coating, the melting line is in wavy type and in the longitudinal cladding, the melting line is in linear type. Although there are differences in the size and morphology of cladding layers structure under different parameters, the research shows that the microstructure is composed of four phases: ?-Co,CrCo,Cr23C6 and M6 C.Microhardness test analysis shows that the process parameters have an important influence on the fluctuation of microhardness, and the influence of the process parameters on the Rockwell hardness is not obvious. The mass loss of Co based alloy cladding layer before and after wear experiment is small, friction coefficient is high, and the friction process fluctuation is small, so its wear resistance is good. The furrow wear scar on worn surface indicates that the wear process is the synergic wear of abrasive wear, adhesive wear and oxidation wear. The tensile fracture of samples belongs to brittle fracture, the fracture is smooth, and there is no necking phenomenon, which indicates that the fracture process is mixed mode fracture of dimple-cleavage-like fracture. The compression test of the sample shows that compressive strength of the cladding layer is good.Laser process parameter is an important factor affecting the quality of cobalt base alloy cladding layer. With the increase of scanning speed, the energy that the substrate got from laser beam reduces, which lead to the reduction of melting amount of the substrate. So dilution rate decreases. Therefore, the increase of scanning speed should be appropriate, the premise is to ensure that the scanning speed can make cobalt base alloy powder melt completely. Overlapping ratio affects the size and morphology of the structure in re-melting zone, and the surface quality of the cladding layer. The melting amount of substrate in the laser beam is increased after the preheating, and the interface region which is combined with the cladding layer becomes wider. Cobalt base alloy element can diffuse into the matrix better, which makes the structure and property of the binding domain transited smoother.Under the same process parameters, the dendrite microstructure of the cobalt base alloy with 10%WC was refined by laser cladding, dendrite arm spacing also is decreased, and hardness and friction coefficient are increased. The wear resistance of the cladding layer is good. Compared with the cladding layer of the Co based alloy without WC, there are WC and W2 C phases in the cladding layer.