Impact Resistance Of Thermal Sprayed WC-12Ni Gradient Coating

In this paper,supersonic flame spraying and ultra-high frequency induction cladding technology are used to prepare a 250 ?m thick WC-12 Ni single-layer coating and the WC-12 Ni gradient of the 50 ?m and 100 ?m thickness Ni60 A interface layer coating on a 17-4 PH stainless steel substrate.Conducted shock experiments with different loads in water medium,and the shock numerical simulation was carried out in the finite element analysis software ABAQUS.The characteristic of the coating are characterized by surface morphology,metallographic structure and microhardness,etc.The response behavior of the gradient coating under impact load is analyzed through the sample impact profile,surface/section damage morphology,model deformation,and stress distribution.The research results show that:The hardness of the WC-12 Ni coating prepared by supersonic flame spraying is between10?11 GPa.The hardness of the Ni60 A coating is about 7.9 GPa.After induction remelting,the hardness of the Ni60 A cladding layer is about 8.4 GPa,and the substrate is 17-4 PH stainless steel.The surface hardness is between 4.1 and 4.3 GPa.The addition of the interface layer forms a hardness gradient between the coating and the substrate.The single-layer WC-12 Ni coating cracked on the surface under both 10 kN and 15 kN loads.Longitudinal propagation cracks and interface propagation cracks appeared on the crosssections.The depth of the impact profile was 0.717 ?m and 0.848 ?m,respectively.The porosity of the impact zone is 2.31% and 2.13%,respectively.The addition of the interface layer can slow down the peeling of the coating surface under impact load and reduce the porosity of the impact zone of the coating.When the thickness of the interface layer is 100 ?m,the porosity of the impact zone is reduced to about 1.4%.The depth of the impact crater of the coating decreases with the increase of the thickness of the interface layer.After adding a 100 ?m interface layer,the depth of the impact profile drops to about 0.4 ?m.After induction remelting,a metallurgical bond is formed between the interface layer and the substrate,the bonding strength is greatly improved,and the damage threshold of the coating is increased.The 100 ?m interface layer sample only shows interface microcracks under 15 kN impact.In the impact process,the contact stress caused by work hardening and deformation is reduced,and the impact pit is basically formed in the first loading cycle.In the case of no serious damage to the sample,the amount of deformation in the subsequent loading process increases very little.Under a load of 10 kN,the matrix deformation of the single-coating model accounted for 7.3%,and the matrix deformation of the 50 ?m and 100 ?m interface layer models accounted for 5.6% and 4.3%,respectively;Under a load of 15 kN,the deformation of the single-coating model matrix accounted for 11.8%,and the matrix deformation of the 50 ?m and100 ?m interface layer models accounted for 8.7% and 8.0%,respectively.The increase of the thickness of the interface layer is beneficial to reduce the amount of model deformation,reduce the proportion of matrix deformation,and alleviate the phenomenon of interface cracking.The surface tensile stress during the impact will cause the initiation of surface cracks,and the increase in the thickness of the interface layer can reduce the surface tensile stress,thereby reducing the risk of surface cracking of the coating.The interfacial cracking is mainly due to the excessive shear stress of S12.When the peak of the interfacial shear stress is greater than the bonding strength of the coating interface,the coating will have delamination cracking.The addition of the interface layer can reduce the S12 shear stress at the interface,and the shear stress at the interface between the interface layer and the substrate decreases as the thickness of the interface layer increases.