Research On Brazing And Liquid Phase Diffusion Bonding Processing Of Ti₂ AlNb Alloy

Ti₂AlNb alloy has the advantage of high melting temperature, low density, high elastic modulus and good oxidization-resistance at elevated temperature. It has been widely used in aerospace and automobile industry. In the practical application of Ti₂AlNb alloy to the components, technology developments not only in alloy design but also in processing, joining is necessary. In this paper, vacuum brazing and transient liquid phase diffusion bonding were used to join Ti₂AlNb alloy. The influence of the filler metals and brazing parameters upon the interfacial microstructure and joint strength has been analyzed for these two different bonding methods and the optimal brazing parameters are identified.Ti₂AlNb alloy was brazed using TiZrNiCu filler metal. Intermetallic compounds Ti₂Ni, Ti(Cu,Al)2, and (Ti,Zr)[s,s] were formed at the interface. With the increase of bonding temperature and holding time, the diffusion of elements Ti, Al, Ni, Cu was fully, the amount of Ti₂Ni, Ti(Cu,Al)2 increased and (Ti,Zr)[s,s] decreased.The formation of plentiful intermetallic compounds Ti₂Ni, Ti(Cu,Al)2 decreased the joining strength. When joined at 940℃for 10min, the largest shear strength was 228MPa. Ti₂AlNb alloy was brazed using TiNiNb filler metal. Intermetallic compoundsTi₂AlNb, Ti3Al, TiNi, Ti₂Ni and Ti[s,s] were formed at the interface. Ti₂Ni and Ti [s,s] was dispersed on the TiNi matrix, which strengthened the mechanical performance of the interface. With the increase of bonding temperature and holding time, the amount of Ti₂Ni, Ti3Al, TiNi increased and Ti[s,s] decreased. Due to the intermetallic compounds connected together and became big blocks, the joint presented brittle fracture and the joining strength was decreased. The joining strength increased at first and then decreased with the increase of bonding temperature and holding time. When joined at 1160℃for 20min, the largest shear strength 308MPa was reached.In this paper, the TLP bonding of Ti₂AlNb alloy using Ni/Ti/Ni interlayers was investigated. Intermetallic compounds Ti₂AlNb, AlNb2, TiNi, Ti₂Ni was formed at the interface. Brittle intermetallic compounds Ti₂Ni and a few TiNi coexisted at the interface. The shape of brittle phases were lamellar and had a little change with the increase of bonding temperature. As the bonding temperature increased, Ti₂Ni was dispersed and strengthened mechanical performance of the interface. When joined at 1000℃for 120min, the largest shear strength was 323MPa. With bonding temperature increased sequentially, the reaction was more fully, Ti₂Ni distributed in blocks, and the joining strength decreased.