Process,Microstructure And Properties Study On Transient Liquid Phase Bonding Of Ti₂AlNb Based Alloy

Ti₂AlNb-based alloy which is Ti-Al intermatallic compounds was considered to be useful in improving the quality while achieving the desired performance in the development of the aerospace vehicle engine industry for its low density,high specific strength and good oxidation resistance.In this paper,Transient liquid phase（TLP）diffusion bonding of Ti₂AlNb based alloy by making use of Ti-Cu-Zr based filler alloy with the thickness of 70μm was used was preformed.There were four kinds of filler alloy whose content of Ti was fixed,and the value of Cu/Zr was 5,3 and 1 respectively and the filler alloy whose Cu/Zr=5 contain trance elements（Fe,Ag,Si,Sn）.The effects of different filler alloy compositions on the microstructure and mechanical properties of the joints were investigated under different bonding processes.The TLP diffusion bonding of Ti₂AlNb based alloy was preformed using filler alloy #2（Ti51.8Cu40Zr7.9,Cu/Zr=5）.The effects of process parameters on the microstructure,microhardness distribution,shear strength and fracture morphology of the obtained joints were investigated.It reveals that when the bonding temperature is higher and the holding time is longer,although the base metal and the filler alloy diffused more full,due to the bonding temperature is too high,the base metal and the filler alloy are recrystallized,resulting in a large number of coarse grains,and the grain boundary directly goes through the joint.The microhardness of the joint increased with the increasing of the bonding temperature and the holding time,and the fracture position of the tensile shear test is also transferred from the center region of the joint to the base alloy region.The effects of different value of Cu/Zr on the microstructures,microhardness distribution,shear strength and fracture morphology of the joints obtained under same bonding process were studied.It reveals that it can obtain integral joint using filler alloys whose value of Cu/Zr is different from each other.With the value of Cu/Zr increased,the size of the acicular solid solution increased,and the content of the Cu element in the joint region tends to be uniform.When the bonding temperature is 1000℃ and the holding time is 1h,the tensile shear fracture position of the joint is close to the interface between the joint and the base metal.With the increase of the value of of Cu/Zr,the fracture mode of the joint is changed to brittle fracture.The TLP diffusion bonding of Ti₂AlNb based alloy was preformed by making use of the filler alloy #1（Ti47Cu38Zr7.4X,Cu/Zr=5）.The effect of different process parameter on the microstructure,microhardness distribution,shear strength and fracture morphology of the obtained joints were investigated.The results reveals that the joint using filler alloy which contains trance elements can be obtained at lower temperature.And the joint obtained under different kinds of process will always appear phase at the center of joint,whose morphology was different from the morphology of other regions of the joint.And it can be found that the phase was rich in Si element via the result of EDS.The microhardness of the joint was increases with the increase of holding time,up to 563.5HV,higher than the microhardness of joint obtained by using filler alloy #2（Cu/Zr=5）under the same bonding temperature.The shear strength is far below the shear strength of joint obtained by using filler alloy #2（Cu/Zr=5）under the same bonding process.Through the EDS analysis,it can be found that there is a large amount of Si at the fracture position.It is shown that the fracture location of the tensile shear test is the central region of the joint.