Study On Residual Stress And Surface Properties Of TC4 Titanium Alloy By Ultrasonic Rolling

Titanium alloys,known as high-performance metals,are widely used in aircraft engine blades,fuselage,landing gear and other key components,owing to their high strength,low density,corrosion resistance and superior thermal strength.In the complex service environments,early fail of aerospace critical components often happen due to fatigue,wear and corrosion.In order to meet the requirements of fatigue resistant manufacturing and long service life of key components in aviation,the TC4 titanium alloy evolution law of surface residual stress and surface properties under the condition of high strain rate and large deformation during ultrasonic rolling is studied.The research work was carried out from the aspects of dynamic mechanical analysis of ultrasonic rolling,finite element simulation,residual stress control and surface macro and micro properties.Based on the principle of ultrasonic rolling,the motion characteristic of ultrasonic rolling was analyzed,and the space motion track of ultrasonic rolling head was obtained,which laid a foundation for the analysis of mechanical behavior of ultrasonic rolling.The relationship between amplitude of dynamic impact force and static pressure and amplitude was obtained through the elastic impact contact theory and the piezoelectric sensor experiment principle,which provided the loading of dynamic impact force function for finite element simulation analysis.With the help of the residual stress model formed by ultrasonic rolling TC4 titanium alloy,the formation and action mechanism of ultrasonic rolling residual stress were studied.The distribution of the residual stress field due to the ultra-high frequency shock wave under ultrasonic rolling conditions,it provided theoretical guidance and basic data for the stress analysis and surface properties research of finite element simulation.Based on the dynamic impact mechanical model,a three-dimensional model of ultrasonic rolling processing was established by ABAQUS finite element(FE),the mesh evaluation was performed,and the simulation of dynamic impact force loading was defined,and the distribution of residual stress on TC4 titanium alloy surface and along the modified layer direction under different static pressure,amplitude and time were revealed.The FE results show that a higher value of residual compressive stress was generated after the ultrasonic rolling,which achieved strain strengthening.The ultrasonic rolling experiment of TC4 titanium alloy under different processing parameters was carried out,and the residual stress of the titanium alloy specimen after ultrasonic rolling was analyzed using a fully automatic gradient stress detection and analysis system.The experimental results show that the experimental values of the residual stress on the surface and along the depth of the layer are in good agreement with the simulation values,which verified the accuracy of the FE model.Combined with SEM and other micro detection results analysis,it was found that the grain refinement modified layer was formed on the surface of the material,and the surface grains were elongated.From the perspective of grain refinement,the reason why the maximum residual compressive stress was located at a certain depth from the surface was explained.Taking the formation of a high compressive stress layer on the processed surface as the optimization goal,the optimal parameter combination of static pressure,amplitude and rolling times were determined,which provided experimental basis and basic data for improving the surface properties of ultrasonic rolling titanium alloy.With the help of surface quality inspection methods,the macro and micro properties(including surface roughness,three-dimensional surface morphology,hardness,friction and wear properties)of TC4 titanium alloy surface under different ultrasonic rolling processing parameters were analyzed.The effect of ultrasonic rolling parameters on surface forming characteristics were discussed.The experiment of roughness and three-dimensional surface morphology revealed that the specimen had high-quality finishing after ultrasonic rolling.The effects of different ultrasonic rolling parameters on the surface hardness and wear resistance of TC4 titanium alloy were quantitatively analyzed by hardening and friction wear experiments.The results show that the micro and macro properties of the material were improved after ultrasonic rolling.