Research On Surface Integrity Of TC4 Titanium Alloy By Ultrasonic Rolling

TC4 titanium alloy has been widely used in aerospace,marine medical and other industries,but the surface strengthening effect of traditional surface treatment technology on titanium alloy is limited,which seriously restricts its further development in the field of high precision.To investigate the effects of different process parameters on the surface integrity of TC4 specimens and the effect of ultrasonic-assisted rolling strengthening on the enhancement of microstructure and mechanical properties of TC4 specimens,this paper uses TC4 titanium alloy specimens as the test object for ultrasonic-assisted rolling strengthening test.The main work and research contents are as follows:(1)Firstly,given two circular objects contact stress and deformation calculation formula,and analyzed the micromachining principle of ultrasonic-assisted rolling strengthening of TC4 titanium alloy.Designed the shape and size of the amplitude transformer used in this processing system,and build the kinetic simulation model of the designed luffing rod based on the finite element simulation method.The simulation results show that the designed longitudinal vibration frequency of the amplitude transformer is19863 Hz and the amplification is 9.791,which verified the accuracy of the design.(2)By designing and conducting single-factor tests,investigated and analyzed the trends and causes of the effects of different spindle speed,feed rate,static pressure and machining times parameters on the surface morphology,hardness and residual stress of the specimen.The test results showed that: within a certain range,the surface shape of the specimen will improve with the increase of spindle speed,static pressure and machining times,and will deteriorate with the increase of feed rate;static pressure and residual stress will improve with the increase of spindle speed,static pressure and machining times,and will decrease with the increase of feed rate,and too large or too small of any kind of process parameters will have harmful effects on the surface quality of the specimen.(3)The degree of influence of the process parameters on the surface integrity of the specimen was derived from the orthogonal test as follows: spindle speed > machining times >feed rate > static pressure.At a spindle speed of n=950 r/min,a feed rate of f=0.08 mm/r,a hydrostatic pressure of F=550 N and a number of machining operations of N=8,an optimum roughness of 0.145 μm is obtained on the surface of the test piece.(4)Observed the microstructure and morphology of specimen sections and discovered that a grain refinement layer with a thickness of about 89 μm was formed on the surface of the specimen after processing.Analyzed the hardness gradient of the surface layer of the specimen before and after processing and found that the layer depth of work-hardening layer basically the same as the grain refinement layer,and the hardness value gradually decreased with increasing depth.Measured the surface nanoindentation curves before and after processing,it shows that the surface modulus of elasticity increased from 96.98 GPa to112.96 GPa after processing and the surface elastic recovery capacity became weaker.The corrosion resistance of the specimens was also greatly improved after processing,and the corrosion rate was reduced by about 80%.