Research On Process Of Strengthening & Toughening And Its Mechanism Of The Joint Interface For Ti₃Al/TC11 By Laser Rapid Forming

Titanium alloy is widely used in aviation, aerospace, shipbuilding, petrochemical and other industries with excellent comprehensive mechanical properties. With the development of various industrial productions, the demand for new materials, new technology is increasingly extensive and urgent, so the properties of single materials can not meet the requirements of industries. Dissimilar alloys composed of different kinds of material are widely concerned because of their advantages and lowly costing. But the interface is the most weak in the joint of dissimilar alloys. As a new technology developed in the late 20 th century, laser rapid forming can sinter metal powder with high-energy laser and manufacture component without moulds. What’s more, its production efficiency is high and its microstructures are compact. So the new technology is generally used in aerospace field.In this paper, Ti₃Al/TC11 dual alloy was prepared by laser rapid forming and the joint interface was improved by isothermal forging plus heat treatment. Finally, the better process parameters and the strength mechanism of the joint interface have been analyzed and obtained. The main research contents and results are as follows:（1） Dual alloys were deformed by isothermal forging plus heat treatment with different strain rates and deformations at 960 ℃, and then compared with the Ti₃Al/TC11 dual alloy by laser rapid forming. The results show that this technology can improve the microstructure obviously. The coarse columnar microstructures in the joint interface are broken by laser rapid forming, and the microstructures become equiaxial, small and homogeneous.（2）Strain rate and deformation amount of dual alloy has a great influence on tensile properties. With the increase of strain rate, the room temperature strength of dual alloy is elevated and the high room temperature is decreased. But at the same time, the room and high temperature plasticity hardly change obviously. What’s more, the deformation has a little effect on room temperature strength and plasticity, but has a great influence on high temperature strength and plasticity. With the increase of deformation, Rm and Rp0.2 increase by 14.7% and 23.0%; z improves by two times from 11% to 23%, and A enhances by 37.6% from 42.5 to 58.5%..（3）Whatever how high is the strain rate and deformation degree, the microhardness of the joint interface after isothermal forging is lower than that of only after laser rapid forming. And along the same curve（the same forging process parameters） the difference in microhardness value decreases, and the distribution is uniform. With the increase of the deformation amount, the microhardness of Ti₃Al/TC11 dual alloy in the transition zone is increased obviously. On the other hand, the microhardness average value of the sample in the transition zone deformed by 50% is higher 70 MPa than that of. The increase range as high as 19%.（4）Strain rate and deformation amount have no effect on the phase composition of the joint interface, they only affect the phase morphology, distribution, content and size, etc. With the decrease of strain rate or the increase of deformation amount, the primary α phase,α2 phase and β phase tend to be equiaxial, and the grain sizes of each phase are increased.（5）Strain rate and deformation amount of dual alloy have a great influence on the alloy element diffusion in the transition zone. With the decrease of strain rate or the increase of deformation amount, the scan line of Ti, Al, Nb in the transition zone and its two sides are gently and the density gradient become small, which is attrituted to the low strain rate. When the deformation amount is increased, the microstructure is refined in the joint interface, the diffusion coefficients are increased and the distances of diffusion to boundary are shorted.