| Plasma spraying technology is often used to enhance the comprehensive properties of the surface of materials prone to failure,but the Fe-based Ni/WC cermet coatings deposited by this method have disadvantages such as uneven deposition layer,poor coating adhesion,stress concentration and large pores.Therefore,it is necessary to develop new coating post-processing technologies.The use of high-temperature assisted ultrasonic rolling can produce a larger amount of plastic deformation than traditional ultrasonic rolling,resulting in a deeper gradient nano-hardening layer,which makes the structure and properties of the high-hardness difficult-to-machine ceramic coating have new characteristics,so as to effectively improve the plasma comprehensive properties of sprayed cermet coatings.In this paper,the cermet coating treated by plasma spray grinding was subjected to surface strengthening treatment at room temperature and high temperature assisted ultrasonic rolling,and the improvement mechanism of high temperature thermal effect on ultrasonic rolling coating was compared and analyzed,and the grinding before and after high temperature assisted ultrasonic rolling was explored.The microstructure and physical properties of the coating were changed,and the regression equation between the process parameters of high temperature assisted ultrasonic rolling and porosity was established.The post-processing process of the layers provides theoretical guidance.The main research results are as follows:(1)The microscopic morphology of the coating was detected by metallographic microscope and SEM electron scanning microscope.The surface of the coating without ultrasonic rolling treatment after grinding has many microscopic defects,high roughness and porosity,and the interior of the coating is soft and hard.The surface is in a state of residual tensile stress;after ultrasonic rolling at room temperature,the coating undergoes strong plastic deformation to form a gradient nanostructure,the structure is densified,the surface microscopic defects are reduced,the roughness and porosity are reduced,and the surface residual tensile stress is transformed into a larger In the state of residual compressive stress,there is no phase evolution;except for 800 °C,the surface roughness of the coating and the size of surface nanocrystals show a decreasing trend with the increase of temperature after high-temperature assisted ultrasonic rolling,and the size of residual compressive stress and pores are improved.The depth of the region increases with the increase of temperature,and the diffusion of elements is accompanied by the formation of new phases and the enrichment of elements,which enhances the activity of element diffusion,is conducive to the formation of carbides and solid solutions,and improves the depth of the hardened layer of surface hardness.Compared with the untreated samples and the normal temperature ultrasonic rolling samples,the overall performance of the coating is improved,and the high temperature assisted ultrasonic rolling treatment achieves the best surface integrity improvement effect under the conditions of 0.4MPa and 600°C;When the temperature rises to800°C,it is easier for the material to transition to an equilibrium state,and the residual compressive stress and the work hardened layer are prone to thermal relaxation,and the surface integrity of the coating deteriorates,thus reducing the microstructure and properties of the material.(2)Through the Minitab software,the experiment scheme between different process parameters(rolling temperature T,static pressure F,preloading depth H)and response value(coating porosity Y)was designed.The second-order regression equation of the coating porosity Y,analyzed the single factor of porosity and its interaction,and finally obtained the best process parameters: rolling temperature of 600°C,static pressure of 0.40 MPa,and preloading depth of0.20 mm.The microstructure and properties of the coating were better under these conditions,which further verified the reliability of the response surface model.(3)The friction factor of the high-temperature assisted ultrasonic rolling coating at 0.4MPa and 600°C is reduced by 93.6% and 66%,respectively,compared with the non-ultrasonic rolling coating after grinding and the normal temperature ultrasonic rolling coating,and the wear loss is heavy.They are reduced by 78.8% and 37.3%,respectively.Due to the synergistic effects of high-temperature-assisted ultrasonic rolling on the improvement of microstructure defects,surface nanoscale,soft + hard phase system enhancement,and residual compressive stress transformation,it has excellent tribological properties. |
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