Study On Processes And Structure Features Of WC-NiCrBSi Coating Prepared By Thermal Spray And Induction Heating

In this paper, the sample of 17-4PH stainless steel coated with WC-NiCrBSi was prepared by flame spray and high velocity oxygen fuel and induction heating. The particle velocity distribution in the flame was studied by high speed camera. The surface roughness of coatings and cladding layers was tested by surface contourgraph. The cross-section morphology was observed by SEM. The hardness distribution was obtained by Micro hardness tester. The porosity was calculated through SEM images. Friction coefficient and specific wear rate was tested by wear experiment.The experiments shows that:(1) the best spray distance of CP-3000 is 200 mm. The smaller the particle diameter is, the higher speed it will be obtained. The velocity of 37-53 μm particles is 110 m/s and 53-105 μm particles is 100 m/s. The porosity and pore diameter will be smaller, when the velocity is higher. The cladding layer has a higher density and hardness. The micro hardness of layer prepared by 37-53 μm particles is 9.5 GPa and 53-105μm particles is 8.0 GPa. (2) When 02 flow is 811 NLPM, the best γ of WokaStarTM-610-Si HVOF gun is 1.11, The powder has the highest speed, about 645 m/s, and maximum flat. The coating is harder and much more compact than flame spray. The micro hardness is 11.60 GPa and porosity is 0.8%. (3) When velocity is 2.5 mm/s and output current is 820～860 A, the higher the current is, the smoother the surface is. The roughness is 4.5 μm when current is 820 A and 3.75 μm when 880 A. The layer has a higher bonding strength and lower porosity, dropping from 0.8% to 0.1%. The substrate has a deeper softening depth, rising from 60 μm to 80 μm. The WC-NiCrBSi layer has a higher roughness,4.0 μm, and porosity,1.7%, when output current is 900 A, because the layer is burned out. (4)When output current is 900 A, the velocity changes from 3 mm/s to 6 mm/s, the rougher the surface is,rising from 4.7 μm to 6.2 μm, and the layer has a poorer bonding strength and higher porosity, rising from 0.3% to 1.5%. The substrate has a shallower softening depth. The softening depth is 65 μm when velocity is 3 mm/s, and the substrate will not be softened when velocity is 6 mm/s. When velocity is 2.5 mm/s, the softening depth rising to 90 μm and porosity rising to 1.7%. (5) The original coating thickness changes from 50 μm to 100 μm, the rougher the surface is, rising from 3.5 μm to 4.9 μm, and the layer has a higher porosity, changing from 0.075% to 0.14%. Much more particles were not melted and penetrating cracks were appeared. The substrate has a little bit deeper softening depth. (6) Induction heating can increase wear resistance significantly; The specific wear rate of original coating is 4.5×10-7 mm3/(Nm), and falling to 1.5 ×lO-7 mm3/(Nm) whenoutput current is 920 A and velocity is 2.5 mm/s.