Large Load Impact Behavior Of WC-12Ni Cemented Carbide Coating Sprayed By Hvof

In the application of hydraulic mechanical parts such as pumps,cemented carbide coatings are not only impacted by large loads,but also in water environment.In order to meet the application requirements of such parts as cemented carbide protective coatings,the experimental study on the impact resistance of large loads in water was carried out.In this paper,the large load impact test method at 5²0 kN and 10²5 Hz is used to evaluate the impact resistance of HVOF sprayed WC-12Ni coating in water environment,and compared with WC-13Ni cemented carbide bulk material.The maximum profile depth,porosity,roughness,micro-hardness and cross-sectional crack density of the impact samples were measured.The surface and cross-sectional morphology of the impact test coating were observed by scanning electron microscopy and surface composition was analyzed by energy dispersive spectrometer.The results show that after 6000 impacts,as the coating thickness increases from 100?m to 300?m,the spray angle increases from 45°to 90°,and the surface profile depth of the coating gradually decreases.The impact load increased from 5 kN to 20 kN,the impact frequency increased from10 Hz to 25 Hz,the surface profile depth gradually increased,and the coating profile depth ranged within 3?m.The depth of the coating profile indicates that the coating is deformed during the impact process,and the surface is work hardened,so that the hardness of the impact area is higher than that of the unimpacted area by 100 to 200 HV_0.3.The contour depth of the bulk material is within 0.8?m,the deformation is smaller than the coating,and the hardness of the impact region is higher than the unimpacted area of 30 HV_0.3.As the load and impact frequency increase,the surface damage after coating impact is transformed by the fragmentation and detachment of WC particles and the Ni bond phase to the center and edge cracks.The fragmentation and detachment of WC particles and Ni binder phase results in a surface porosity growth rate of up to 250%and a surface large pore ratio of up to 40%,which increased surface roughness and damage.The surface damage form of the bulk material is WC particle spalling and crack along the Ni bond phase and surface porosity growth rate is as high as 150%,and the large pore proportion is as high as 80%,which is much higher than the coating large pore ratio and the surface damage.As the load increases,the cross-sectional failure mode of the coating changes from WC particles spalling to four types of cracks,and 15 kN is the threshold for cross-section crack initiation.The crack density increases from 0 to 420?m²/mm².An increase in the thickness of the 45°spray coating reduces the crack density,while increasing the thickness of the 90°spray coating to 300?m increases the residual stress and produces more cracks.In contrast,an increase in the impact frequency does not promote cross-section cracking.The number of impacts is increased to 360,000 times,the surface profile depth is up to 15?m,the coating deformation is increased,and the hardness of the impact region is higher than that of the unimpacted area.In particular,the surface of the coating under 20 kN impact caused the hardness of the impact area to be lower than that of the unimpacted area due to excessive cracks.After impact,the surface porosity growth rate of the coating is up to 150%,the large pore proportion is in the range of 0³5%,the surface edge crack and center crack increase,and the surface roughness increases.As the load increases,the cross-sectional crack density increases from 0 to 650?m²/mm²,the cross section crack initiation threshold is reduced to 5 kN,the crack is widened,and the coating has large flaking failure.Both the thickness of the coating and the increase of the spray angle can reduce the surface deformation of the coating under the impact of large load,thereby reducing the surface crack and cross-section crack damage to the coating and improving the impact resistance of the coating.