| Steel 45 has been widely used as a high quality carbon steel for mechanical components,which operate under extreme working conditions with high loads and most mechanical components fail mainly due to surface wear.The wear process produces micro-cracks on the surface,which gradually sprout and expand into large crack sources under the working load,and finally the whole part is fractured and scrapped.Previously,plasma spraying technique was used to prepare wear-resistant Ni-WC coating on the surface to improve its service life.However,the Ni-WC coating has large surface defects,more cracks and pores in the internal coating tissue,higher residual tensile stress,and low bond strength and cohesive strength.In this study,High temperature + Ultrasonic deep rolling(HT+UDR)was used for post-treatment of Ni-WC coatings to improve surface defects,structure and strengthening properties.A singlefactor test was used to investigate the influence law of the preloading depth under the main process parameters of ultrasonic deep rolling on the microstructure and mechanical properties of Ni-WC coatings,as well as the influence of tribological properties.The main findings are as follows.(1)Characterization and analysis of the surface morphology and microstructure of Ni-WC coatings after different preloading depths of HT+UDR showed that.The specimens were not ultrasonically deep rolled with uneven surface morphology,unmelted particles and pores,cracks inside the tissue,and poor density.After high-temperature ultrasonic deep rolling treatment,the surface morphology of the coating is more flat,and the cracks and pores in the internal microstructure are basically eliminated,with the increase of the preloading depth,the surface morphology and microstructure of the coating are improved first and then material peeling and fine lines appear.After HT+UDR,elemental diffusion occurred at the interface of Ni-WC coating and substrate bonding,and the XRD pattern showed that a new phase was generated with the same diffraction peaks under different preloading depth treatment,but shifted and broadened.The porosity decreases with increasing downward pressure,reaching a minimum of 2.45%.(2)HT+UDR treatment of Ni-WC coatings,the main strengthening mechanisms are fine grain strengthening,work hardening and stress strengthening.The surface roughness was improved with the best preloading depth at 0.25 mm,which improved by 60% relative to the not ultrasonic deep rolled specimens.The hardness of the coating section increases and then decreases with the increase of the preloading depth,and the maximum section hardness after different preloading depth treatment is 610.5 HV0.1,726.3 HV0.1 and 685.3 HV0.1respectively.HT+UDR transforms the residual tensile stresses on the coating surface into residual compressive stresses,and a continuous increase in the preloading depth leads to an increase in the dynamic recrystallization behavior of the surface and a decrease in the residual compressive stresses.(3)HT+UDR has a significant improvement on the tribological properties of the coating,with a significant reduction in the coefficient of friction and wear.Not ultrasonic deep rolling coating wear surface for serious three-body abrasive wear and fatigue wear,the preloading depth to reduce the surface defects,the coating hardness increases,nickel-based alloy region and WC hard particles mosaic structure more closely,play a strong bonding role.At a preloading depth of 0.25 mm,the coating wear was in the form of slight abrasive wear,and the friction coefficient decreased to 0.04,with a 73.1% reduction in wear relative to the not ultrasonic deep rolled coating. |
PDF Full Text Request