Study On Off-angle Deposition Process And Microstructure Of WC Particles Reinforced Composite Coatings By HVOF

In this paper, the sample of 17-4PH stainless steel coated with WC particles reinforced composite coatings was prepared by high velocity oxygen fuel and induction heating. Coatings were prepared by off-angle spraying. Deposition rate of coatings was obtained by parameters of HVOF. The cross-section morphology was observed by SEM and metallurgical microscope. The surface roughness of coatings and cladding layers was obtained by surface contourgraph. The hardness distribution was tested by Microhardness tester. The porosity was calculated by SEM images. Tensile strength and elongation and fatigue life was tested by fatigue experiment. The experiments shows that:(1) The coating thickness of ?19 cylinder specimen is 50-60 ?m. The two WC particles reinforced composite coatings are prepared by induction heating. The output current of Ni60A coatings is 700-740 A, the output current of Ni6040WC coatings is 760-780 A. When the output current of Ni60A coating is 700 A, the microhardness of cladding layer is 8.0-8.5 GPa and the softening depth is 0. when output current is 740 A, the microhardness is 6.0-7.5 GPa and the softening depth is 40 ?m. When the output current of Ni6040WC coating is 760 A, the microhardness of cladding layer is 8.0-9.5 GPa and the softening depth is 30 ?m. when output current is 780 A, the microhardness is 8.5-9.5 GPa and the softening depth is 50 ?m. (2) The bigger the spray angle is, the higher in small amplitude the deposition rate is and the lower the surface roughness is and the higher the microhardness is. After induction heating, the surface roughness and the microhardness is reduced. The bigger the spray angle is, the higher the microhardness of cladding layers is. For Ni60A cladding layer, the microhardness is 5.5 GPa when the spray angle is 30°, the microhardness is 7.5 GPa when the spray angle is 90°. For Ni6040WC cladding layer, the microhardness is 6.0 GPa when the spray angle is 30°, the microhardness is 9.5 GPa when the spray angle is 90°. (3) The cladding layer thickness of (p4 test specimen is 50-60 ?m prepared by HVOF and induction heating. The output currents of Ni60A and Ni6040WC coating are 860 A and 880 A respectively. The lower the velocity is, the lower the porosity is. The microhardnesses of Ni60A and Ni6040WC cladding layers are 9.5 GPa and 8.5 GPa respectively. (4) There are the most axial tensile strength and elongation for the substrate,1193 MPa and 1.575% respectively. The axial tensile strength of the test specimen coated Ni60A is the smallest. The axial tensile strength of the test specimen coated Ni60A when the spray angle is 45° is larger compared to the one when the spray angle is 90°; the axial tensile strength of the test specimen coated Ni6040WC when the spray angle is 45° is smaller compared to the one when the spray angle is 90°.The elongation of the test specimen coated Ni60A is larger compared to the one of the test specimen coated Ni6040WC. The elongation is bigger when the spray angle is 45°. (5) The surface polishing and heat treatment can increase fatigue life of test specimen prepared by induction heating. The test specimens by sand-blasting and ultrasonic cleaning also exhibit higher fatigue lives compared to the specimens without ultrasonic cleaning. The fatigue life of the test specimen with cladding layer prepared by 45° spraying and induction heating is higher than that of the test specimen with cladding layer prepared by 90° spraying and induction heating.