Influence Of Cu Content On Microstructure And Tribological Properties Of Ni60 Coating With Directional Structure

Using Cu element to modify the Ni-based alloy directional structure coating,the Ni60/Cu directional structure composite coating was prepared by thermal spraying+induction remelting+forced cooling composite technology.Setting the added mass fraction of Cu element to 5%Cu,10%Cu,15%Cu and 20%Cu respectively,the influence of Cu element addition content on the microstructure,phase evolution,element distribution,mechanical properties and friction and wear properties of thermal sprayed prefabricated coatings,high-frequency induction remelting coatings and forced cooling formed Ni-based alloys with directional structure has been systematically studied.The systemic influence mechanism of Cu element addition on the coating from thermal spraying,high-frequency induction remelting,to the microstructure evolution and performance of the directional structure coating was discussed.And the effect of cooling strength on the microstructure and friction properties of the coating under the optimum amount of Cu addition was studied,and the following conclusions were drawn:1)The addition of Cu element promotes the grain boundary fusion of the flame sprayed prefabricated coating,refines the laminar structure,but reduces the lateral expansion ability of the Ni60 alloy;Induction remelting eliminates the laminar structure formed by the prefabricated sprayed coating and forms a solid-state coating.Remelting makes the Cu element to diffuse into the crystals,promotes the precipitation of solute elements,and promotes grain refinement and grain boundary evolution.With the increase of Cu element content,the microstructure in the coating is gradually promoted to form"martensite-like structure"and"bainite-like structure".The grains of the directional structure coating formed by forced cooling grow from the interface to the surface in the form of columnar dendrites.The Cu element in the directional structure coating enriched in the crystal grains,which promotes the enrichment of Cr,C,and B elements in the grain boundary area.The amount of Cu added has a significant effect on the orientation,grain morphology and size of the directional dendrite growth.When the Cu addition amount is 15%,the directional dendritic structure is fine,and it grows vertically along the interface.2)The strong metallurgical compatibility of Cu and Ni elements promotes the recrystallization ability of the composite alloy coating.In the process of continuous diffusion to the crystal grains,Cu and Ni solid solutions and compound phase CuNi are formed,which promotes Cr,B and C precipitate toward the grain boundary,and then refine the microstructure.At the same time,the growth morphology of the interface eutectic structure evolves,so that as the Cu content increases,the dendrite orientation changes significantly during the formation of the directional structure coating.3)With the increase of Cu content,the friction coefficient and volume wear rate of prefabricated spray coating,induction remelting coating and directional structure coating all show the law of first decreasing and then increasing,indicating that the addition of Cu element can effectively enhance the coating the antifriction performance of the layer,the 15%Cu content coating showed the lowest friction coefficient and wear amount,indicating that the 15%Cu added coating exerted the best anti-friction performance;However,when Cu is 20%,the addition of a larger amount of Cu will cause the adhesive wear of the coating to become serious,resulting in a decrease in the wear resistance of the coating.4)The crystal grain orientation evolution of the directional structure coating with15%Cu content and the effect on the friction performance at the cooling rate of0.944m L/(min·mm~2),1.886m L/(min·mm~2)and 2.831m L/(min·mm~2)are studied.Studies have shown that the cooling intensity has a significant impact on the microstructure of the oriented crystal.When the cooling water flow rate is2.831m L/(min·mm~2),the directional structure of the coating is obvious,the columnar dendrites are developed and regular,and the grain boundaries are fine.However,it has no significant effect on the phase evolution and hardness properties.The wear resistance test shows that the coating under the flow rate of 2.831m L/(min·mm~2)shows the lowest friction coefficient and wear rate,the width of the wear scar is also the smallest,and the friction surface is smooth.It shows that the stronger cooling strength can promote the regular growth of the directional structure of the coating and enhance its wear resistance and friction reduction performance.