Microstructures And Properties Of TC4Titanium Alloy Treated By Shot Peening

As the performance of good biological compatibility, high specific strength and great corrosion resistance, Ti and TC4titanium alloy were widely used in chemical, aerospace, spaceflight, physical and medical industries et al. But, because of the poor anti-fatigue performance and wearability, the further development of TC4titanium alloy was limited. Therefore, it had a great value in theory and social benefit to improve the anti-fatigue properties of TC4titanium alloy.To improve the tensile fatigue performance of the TC4titanium alloy, mechanical shot peening was used in this paper to strengthen the surface. The microstructures and mechanical properties of TC4titanium alloy were also investigated by means of OM、XRD、TEM、SEM、EBSD and mechanics performance testing. This paper mainly studied the following four aspects:(1)"dry shot peening","dry+wet shot peening""wet shot peening" were assessed comprehensively by surface performance testing to find the optimum technological process.(2)Investigate the effect of air pressure, proportion of solid and liquid, coverage, standoff distance, shot angle and other parameters on the mechanical properties, and then establish the optimum technological parameters to improve the fatigue properties of TC4titanium alloy.(3) Analyse the mechanism of microstructures after wet shot peening, explore the mechanism of shot peening strengthening which will serve as surport for the engineering practice. The results were as follows:1. Results from surface performance testing indicated that:(1)The surface damage under wet shot peening was the slightest, the one under composite shot peening took second place, the one under dry shot peening was the most serious, and the roughness after dry shot peening was a few times bigger than the wet.(2)The surface of dry shot peening had a lowest residual stress and a deepest pressure zone, the surface of wet shot peening got the opposite results, and the composite shot peening got the results between them.(3) It was available through anti-fatigue properties testing that the fatigue limits of these three kinds of shot peening:The fatigue limit of original specimen was605MPa, of the dry shot peening was500MPa, of the composite shot peening was670MPa, and of the wet shot peening was680MPa, increasing by12.4%. It followed That the wet shot peening had a most effect on improving the fatigue strength of TC4titanium alloy.2. The analysis of the microstructure under wet shot peening indicated that wet shot peening reduced the grain size observably which was between20～100nm reaching nano size. It was beneficial to the increase of hardness and fatigue strength.3. Comparing all these technological parameters of wet shot peening it can be known that the most important influencing factors on the fatigue properties of TC4titanium alloy were:proportion of solid and liquid, air pressure and coverage. Among them, the best proportion of solid and liquid was13:1, the best air pressure was0.4MPa, the best coverage was400%, Besides, the best angle of shot peening was90°and the best standoff distance was150mm.4. The fatigue properties compared in different grain sizes of TC4titanium alloy indicated that:the fatigue limit of10μm is605MPa, it can be increased to680MPa by wet shot peening; the fatigue limit of3μm is640MPa, it can be increased to830MPa by wet shot peening. The result above indicated that with the decrease of the grain size, the fatigue strength became better, the strengthening effect became more obvious.