Recently, the demand on Titanium has grown rapidly. Especially in the sports industry, by using Ti-3Al-2.5V alloy which does not require the high temperature property and yet has similar mechanical property to Ti-6Al-4V alloy, the orthopedic production technology is being developed to simplify and raise the quality.
The Superplastic forming (SPF) has so great the strain even under the low stress that it can lower the production cost through the high shaping accuracy of product, the minimization of residual stress and the high design flexibility. Diffusion bonding (DB) has the characteristics to bond the two solid materials in the high temperature and pressure through the diffusion and to easily form the structures of high complexity and specific stiffness when it is used along with SPF.
In this study, the SPF and DB technologies that had never been applied to the sports industry in domestic were applied to the production of bike frame to establish the forming technology of Titanium material. Presently, as there are no appropriate forming technologies, the Titanium frames are usually produced with the fusion bonding of cylindrical tubes in order to reduce the weight, which causes the quality problem on the welded sections. To remove the present problems on the welded parts such as thermal deformation, uneven bonding strength and residual stress, the SPF and DB technologies were applied for the improved quality. But, there have been few studies about SPF and DB technologies for 2 and 3-axes with Ti-3Al-2.5V alloy tubes as well as about the temperature condition and holding time for the process.
In this study, to apply the SPF and DB technologies, the heat treatment experiment was carried out with the variable of holding time under the temperature condition that could be super plasticity. Through the observation of micro structure in the experiment, the data base for the forming was constructed. Based on the microstructure data base, the appropriate temperature for the SPF and the holding time for the DB were drawn out. Then, two Ti-3Al-2.5V tubes were bonded in T-shape through the consecutive process of SPF and DB, and the characteristics of microstructure on the connection part were analyzed.