Study On Technology And Mechanism Of Diffusion Bonding Ti₃Al And Ti₂AlNb Alloy

Due to its low density, high strength, superior oxidation resistance and creepresistance, Ti₂AlNb alloy is an ideal material for aeronautic and aerospace application.However, the density of Ti₂AlNb is much heavyer than Ti₃Al because of the content ofNb. Thus, reliable joining Ti₃Al and Ti₂AlNb, which can expand its application scope andreduce production cost, would make a profound difference to aerospace materials. In thispaper, Ti₃Al and Ti₂AlNb were bonded by solid diffusion bonding directly and with Tiinterlayer. Optimal diffusion paremeters as well as bonding mechanism were indentifiedand the effect of bonding parameters on interface microstructure and mechanical propertywere discussed.Ti₃Al and Ti₂AlNb were bonded by solid diffusion bonding directly. There weresome stick O-phase at the interfacial joints, and some B2-rich phases near the Ti₂AlNb.The bonding joints was bonded favorable and the elments were diffused adequately whenthe temperature ranged from950℃to1000℃and the bonding time ranged from60-90min. The shear strength could reach to635MPa and the tensile strength could reachto795MPa under the optimum technological process. Both of the joints fractures were inthe Ti₃Al-base alloy. Further more, the diffusion mechanism was also illustrated in thepaper. However, the properties of Ti₃Al alloy were degraded due to the high temperatureduring the diffusion bonding.Ti₃Al and Ti₂AlNb were bonded by solid diffusion bonding with pure Ti interlayer.The typical interfacial microstructure of joint bonded with pure Ti interlayer wasindetified to be Ti₃Al/+β/B2-rich/Ti₂AlNb. With the increase of thickness of Ti foil, theshear strength reduced gradually. In final, the10μm of Ti interlayer was used for study.The shear strength could reach651MPa and the tensile strength could reach906MPaunder the parameter of T=900℃, t=120min, P=5MPa, and also both of the jointsfractures were in the Ti₃Al-base alloy.The adding of Ti interlayer improve the property ofTi₃Al alloy and decreased bonding temperature for about100℃, made the tensilestrength enhanced.The extent for element diffusion in the joint of Ti₃Al/Ti/Ti₂AlNb, Ti₃Al/Ti andTi/Ti₂AlNb was indentified by studying diffusion mechanism and kinetic equation forelement diffusion. The effect of concentration gradient during diffusion process wasanalysed. The diffusion equation of elements Al and Nb was established in Ti₃Al/Ti andTi/Ti₂AlNb.