TC4 Titanium Alloy Diffusion Bonded Interface Characters And Simulation Of The Voids Shrinkage

Titanium alloys have been applied extensively in the aerospace filed due to their significant advantages such as high specific strength, excellent corrosion resistance and good heat resistance, and their joining technology is a key to the engineering applications. In this thesis, two kinds of TC4 Titanium alloys with different grain sizes (GS) were joined by diffusion bonding process respectively. The joint interface characters and their evolution with parameter were comparing studying. In additional, the void shrinkage model in diffusion bonding was established, and the voids shrinkage process was simulated.The metallographic analysis and statistical results of interfacial voids indicated that, whatever GS TC4, increasing bonding temperature (T), pressure (P) and time (t) can decrease the volume of interfacial voids, and thus increasing the bond ratio for the joints. However, when the same bonding parameters were used, the smaller the GS is, the faster the interface voids close and the better the joint quality is.Through the analysis of the interface characters, comparing to the influence of T and t on the interface microstructure, P contributes less. For the volume fraction ofβ, when the GS of Titanium alloy is larger, it reduces first and rises afterwards with T elevating, and increases earlier but decreases later as t prolongs; while the smaller GS, it increases slowly when T rises, and increases earlier but decreases later as t extends. For the size ofβ, when the larger GS , it increased in company with the elevation of T, and increased earlier and decreased later as t continued; while the smaller GS, it enlarges both as T and t increases. And for the quantity ofβ, when the larger GS, it reduces with T rising and increases as t protracts; while the smaller GS, it reduces when T rises, and elevates earlier and drops later as t prolongs.On the basis of the established model, the shrinkage of voids in the diffusion bonding process was simulated. From the simulation result, creep mechanism contributes most, surface source mechanism the next, and interface source mechanism the least for the voids shrinkage during diffusion bonding process. The surface source mechanism nearly ceases when the bonding time reaches enough. The predictions were compared with the experiment data for TC4 and in general show good agreement, which approved rational of the model.