Effect Of Nanocrystallization In Surface Layer On Fatigue Strength Of Commercial Pure Titanium By High Energy Shot Peening

Possessing many advantages such as high strength and low density, good corrosion-resistance and good high temperature properties, Titanium and titanium alloys are widely used in the space flight and aeronautic industries, the martial industry and civilian industry. But the further applications of the materials are confined due to its poor wear-resistance, low fatigue strength and fatigue reliability. Although the methods of physical or chemical surface treatments to enhance the wearing resistance of Titanium and its alloys, almost these methods are not effective on improvement of their fatigue strength.Shot peening and rolling are the well-known methods that can increase the fatigue limit of Titanium and its alloys, however, the invigoration effect is limit. The surface nanocrystallization is known as one of the important methods to modify surface physical, chemical and mechanical properties, and prolong using life of machinery parts. The technique of nanostructures surface layer in metals and alloys is with most important significance for the industry application.In the present study, the nanocrystallization in surface layer of the rotary bending fatigue notch specimen (Stress concentration factor K_t=1.27) of commercial pure titanium was carried out using the high-energy shot peening (HESP). And the microstructure , microhardness mensuration and surface roughness were observed or analyzed before and after the surface nanocrystallization. Then the rotary bending fatigue test is performed, and the maximum stress at which the specimen is not broken at 10~7 cycles is defined as fatigue limit.(1) Surface nanocrystallization can be performed by HESP, and grain sizes were several ten nm.(2) The fatigue test results show that the fatigue limit of the commercial pure titanium after surface nanocrystallization was increased by 34%,...