Structural Design And Optimization Of Super Thick CrN Coating Under Gradiet Young's Modulus

CrN coatings have been used as the research object because of their high hardness,corrosion resistance and oxidation resistance.Many scholars have studied thermal stress and mechanical simulation of nanoindentation of CrN multilayer coatings long ago.Howeve,for more multilayer CrN coatings,the thermal stress of CrN coatings with gradient Young's modulus and the mechanics of nanoindentation have been studied.The simulation has not been studied yet.When the coating is thicker,the film is easy to peel off,and the interface bond between the film and the substrate will become worse.Therefore,it is necessary to further explore and design a more reasonable coating structure to meet the need of industry and military.In this paper,the super-thick CrN coatings with whose thicknesses is greater than 10 ?m are studied.10 ?m,15 ?m and 20 ?m with layers of 16,32 and 64 are selected as the research objects.The thermal stress of the coatings and the mechanical properties under nanoindentation are compared by designing the gradient of the multilayer coatings.The stress laws under different gradients,thicknesses and layers are obtained.Thermal stress occupies an important part of the coating stress in the preparation process.When the gradient index is 0.25,0.5,1,2,12,the thickness is 10?m,15?m,20?m and the n?mber of layers is 16,32 and 64,two variables remain unchanged.By changing one variable,the correlation between several variables and the thermal stress of the coating and the stress under nanoindentation is analyzed.The following conclusions are drawn:(1)The thermal stress of the coating is hardly affected by the n?mber of layers of the coating.The thickness of the coating only prolongs the path of stress distribution without changing the n?merical value of stress.With the increase of gradient index,the von Mises thermal stress in the coating increases.When the gradient is 12,the stress along the path of the coating is the greatest,but at the position of the base interface and the surface of the coating,the large stress value is in several steps.The radial stress distribution in the coating is along the thickness direction.With the increase of the gradient,the radial compressive stress value increases gradually.(2)When nanoindentation is loaded to the maxim?m position,the radial stress along the thickness direction of the coating is obviously affected by the n?mber of coating layers when the gradient index is small.When the gradient index is large,the n?mber of coating layers has almost no effect on the radial stress.When the gradient index is larger,the radial compressive stress in the coating increases.When the gradient index is greater than 1,the radial compressive stress exceeds the yield strength of 11.6 GPa.When the gradient index is 0.25,the radial compressive stress in the coating is the smallest.(3)After unloading,the von Mises stress gradient is smaller,the more coating layers,the smaller the von Mises stress value,which indicates that the stress can be released better when there are more layers.(4)In the von Mises stress nephogram concentration area,the maxim?m radial stress concentration point is at the contact edge between the surface coating and the indenter in several layers of coatings near the indenter,while in the area below the indenter,the compressive stress concentration area is different under different gradient exponents.The maxim?m shear stress is concentrated in several layers of coating near the middle part.