Investigation Of Laser Surface Texture On The Forming Mechanism And Fatigue Property Of Ni60 Sprayed Coatings

Plasma spraying coatings have been widely applied to the surface in part to improve its corrosion resistance,wear resistance and fatigue resistance.But crack and porosity defects occur in the coatings as the sprayed coatings are constituted by the piling up of sprayed particles,and the bonding type between coatings and substrate is mechanical anchoring which leads the low adhesion strength of coatings.Therefore,sprayed coatings are easy to failure in the process of service.The failure of the coating will result in the instability of the entire service system and a great loss to the national economy.It is necessary to improve the performance of coatings according to its failure characteristics and the service environment.Laser texture processing is an effective method to improve interface and surface properties of coatings.However,research on surface texturing improving the sprayed coatings performance is very limited.In this paper,texture were prepared at the interface of Ni60 sprayed coatings to improve its adhesion strength,discussing the mechanism of surface texturing increasing the bonding strength of coatings combined with image processing software?Image Pro Plus?;The technique of collection for single particle was used to acquire the deposition morphology of particle,analyzing the influence of surface pattern on the spreading behavior of sprayed particles,and studying the deposition mechanism of sprayed coatings on the textured surface;The influence of texturing parameters on the wettability of the spraying particles in high temperature was explored and the relationship between the strength and roughness parameters of the coating was established;At the same time,the texture was prepared on the surface of coatings,and the rolling contact fatigue life of textured coatings was investigated using YS-2fatigue test machine.The rolling contact fatigue life of sprayed coating with different bonding strength was predicted.The influence of texture pattern on the adhesion strength of sprayed coatings was investigated and compared with adhesion strength of sandblasting pretreatment?50MPa?,and the factors influencing adhesion strength was discussed which was resulted from the variance of texture pattern.The results show that additional contact area ratio at interface increases by1.28 times after laser textured treatment with groove pattern,and the adhesion strength of coatings with groove pattern is 58MPa.Adhesion strength of coatings with square pattern texturing is 33MPa,and the adhesion strength of sprayed coatings present obvious variance with different texture patterns at interface because the different texture shape changed the contact area ratio,the density of dimples and the area of plane zone at interface.Meanwhile,the coatings near interface after laser treatment present the smaller grain size which can prevent the crack extension during the tensile process.The influence of texture parameter depth?H?,diameter?D?and distance?L?on the filling state and forming behavior of coatings was discussed,and the interaction of texturing parameters on the boding strength of coatings was explored.Results show that with the texture depth increasing air pore occurs inner the texture dimple,and the adhesion strength of coatings depends on the competition mechanism between the additional contact area ratio and the air pore volume?Vt?inner the dimple;Adhesion strength of coatings increase with the texture diameter increasing and decrease with texture distance increasing.The texture diameter influences the wetting behavior of particles inner the dimples and the texture distance changes the bonding type between sprayed particles and plain area;considering the interaction of the parameters of the texture,the diameter to distance ratio?D/L?of texture is the direct parameter that affects the bonding strength of the coating.The relationship between roughness parameter and wettability of sprayed droplets was investigated.The roughness parameter of textured surface was extracted gradingly through the wavelength limit of Gaussian passing ratio,and the relationship between bonding strength and roughness amplitude parameters?Ssk,Sku?was established.Results show that contact angle of sprayed droplet increases with the increasing of amplitude parameter S_skk and spatial parameter S_tr,while contact angle of sprayed droplet decreases with the increasing of amplitude parameter S_ku and spatial parameter S_al.Nanoscale debris of laser textured surface is beneficial for improving the amplitude parameter S_kuu which can increase the wettability of sprayed particles with substrates.The amplitude parameters?Ssk,Sku?of the roughness can be used to establish the relationship with the bonding strength of the coating,but the variance tendency of adhesion strength with amplitute parameter can be confirmed by relationship between the texture diameter and the particle size of the spraying particle.The mechanism of surface texture improving the rolling contact fatigue property of spray coating was studied,and results show that the interfacial texture can improve the adhesion strength of coatings and thus effectively improve the laminated failure under the contact fatigue condition;fatigue life of the coating with different bonding strength?50MPa,60MPa and 70MPa?was predicted,and the results show that with the increase of the bonding strength,the characteristic life of the coating?failure life of the failure probability P is 62.5?rise from1.233 to 1.415 and 1.995 respectively.The influence of surface texture diameter and density on the rolling contact fatigue property of coatings was studied.Results show that surface texturing increase with the diameter of the texture as the accumulation inner and around the dimples increase gradually,and the contact fatigue property of the coating increase first and then decrease.Carrying capacity of coatings decrease with the increasing of texture density,thus contact fatigue property of the coatings increase first and then decrease.