Effect Of Ultrasonic Deep Rolling On The Surface Microstructure And Fatigue Performance Of TC4 Under High-frequency And Ultrasonic Loading

Titanium and its alloys are widely used in aerospace,biomedical,chemical industries and other fields due to the excellent properties as high specific strength,strong corrosion resistance and superior biocompatibility.With the development of mechanical industry,the fatigue performance of titanium alloys became more and more important.Therefore,surface enhancement technologies have been researched.The effect of various mechanical surface treatments on the surface integrity and fatigue properties of Ti-6A1-4V were reviewed in this paper.In addition,the effect of ultrasonic deep rolling(UDR)on the surface microstructure,high-frequency and ultrasonic fatigue performance were detailed tested and analyzed in the present investigation.The conclusions can be summarized as follows:(1)Ultrasonic deep rolling can effectively reduce the surface roughness of TC4,improve its surface hardness,refine the surface grain,and introduce a residual compressive stress layer on the surface of TC4.(2)After the high frequency fatigue test and the ultrasonic fatigue test,the fatigue life of ultrasonic deep rolled TC4 decreased.The reason was that the ultrasonic deep rolled TC4 was much easier to overheat than the untreated TC4 because of its non-homogeneous microstructure.(3)The surface gradient structure of ultrasonic deep rolled TC4 samples became more uniform after vacuum heat treatment.The fatigue life of UDRed TC4 increased slightly after heat treatment at 200 ? and 300 ?.But the fatigue life greatly reduced when the temperature was increased to 400 ? and above.(4)Compared with the ultrasonic fatigue loading,the relaxation speed of the residual compressive stress on the UDRed TC4 was faster during high-frequency fatigue loading under the same stress amplitude,and the residual compressive stress after high-frequency fatigue loading was smaller.