Microstructure And Properties Of Laser Cladding Ni - Based Tungsten Carbide Coatings

Metal surface coating is a very effective way to improve the metal surface performance, can be the method to increase wear-resisting, corrosion resistance and hardness. So the researching of the coating and coating material property is very meaningful. We use NiCrBSi and WC to be the cladding materials, use semiconductor laser to make the metal ceramic composite coating in the surface of Q235 steel and by changing the laser power, scanning speed and the scale of WC in the cladding material to discuss the influence of the various process parameters to the microstructure and properties of cladding layer. Eventually get excellent performance of Ni based WC metal ceramic composite coating.Using OM, SEM, XRD, EDS to observe the microstructure of cladding layer, we can find that a very strong metallurgical bond has been formed between the cladding layer and matrix. But with the increasing of laser power and the reducing of scanning speed, cladding layer width increased, accompanied by the generation of porosity. The layer has a lot of defects such as the surface roughness increased, a splash, local sag. The layer absorb more energy in unit time, residual WC particles in the coating and around the continuous block of W2C, Cr7C3 CrB, Ni3B, carbide and boride hard phase is also has a large number of decomposition, massive grain structure increased. When the laser power is 2.2kw-2.6kw, scanning speed is 300mm/min-500mm/min, the WC content is 60%-70% can obtain a good cladding layer.When to measure the mechanical properties of cladding layer, compare Ni60 coating with Ni60/WC coating. In the researching, we can find that the hardness rule of Ni60/WC coating is increase gradually until the middle to get the maximum, begin to falling in the fusion zone. With the power increases, the hardness value is bigger, but when the power is too large to make the coating in various phase decomposition and generates a large number of dendrites and reduces the hardness of the coating. When the P=2.6kw, coating reach maximum hardness is 580HV0.3, When the V=500mm/min, the coating hardness reaches maximum 600HV0.3, six times of substrate material. Ni60 coating hardness under the same conditions can be achieved 270HVo 3. With the increase of scanning speed, the coating wear was reduced from 6.6mg to 3.9mg, the wear rate was reduced from 0.37 to 0.2, the wear resistance were enhanced. Add WC in cladding layer of ceramic particles can improve the coating hardness, friction and wear properties, but reduces the coating corrosion resistance.