Surface Nanocrystallization And Properties Of Ti6Al4V And Commercially Pure Ti

Nanocrystalline materials have the unique mechanical, physical and chemical properties, which are different from the routine material owing to the particularity of structure. Most of failures of material begin from their surface, obviously a nanostructured layer can enhance the whole properties and behavior greatly by means of surface nanocrystallization. So surface nanocrystallization has been regarded as one of the most promising technologies.The surface nanocrystallization of Ti6A14V and commercial pure titanium was achieved by means of using shot peening equipment commonly used in industry by modifying shot peening equipment and the parameters. X-Ray diffraction (XRD), the scanning electron microscope (SEM) and the transmission electron microscope (TEM) were used to study the microstructure. It was demonstrated that the grain size of surface was about 20nm, in the nanocrystallization processing of α and β phase composition, the first was α phase and β phase need more energy and longer time.The thermal stability of surface layers of commercially pure titanium theated by high energy shot peening was studied, and the results show that the grain sizes of pure titanium surface layers have increased at 450°C evidently. The grain sizes increase with annealling temperature but they are smaller than that even annealed at 500 ℃.This thesis has been also studied further the effect of surface nanocrystallization on the fatigue properties of commercial pure titanium induced by high energy shot peening, and it was compared the effect of surface microstructures on the fatigue property of commercial pure titanium induced by high energy shot peening with normal shot peening through the microstructure, hardness, residual stress and the fatigue fracture. It indicated that these two methods can improve the effect of fatigue, but that of high energy shot peening improved 12% on fatigue effect lower than that of normal shot peening 18%. According to the analysis of fatigue fracture, it has shown that there are some damages in the surface of the commercial titanium and these damages can become fatigue crack easily, so these maybe account for the effect which induced by high energy shot peening improved lower than that induced by normal shot peening.