Microstructure And Property Of TLP Points For A Ni-based Single Crystal Superalloy

Ni-base single crystal superalloy has excellent high-temperature mechanical properties,the transient liquid phase(named as TLP)bonding is a kind of bonding technology for the superalloy which is difficult to be welded by fusion welding.In this dissertation,the Ni-base single crystal superalloy was bonded by TLP method using NiCr-B and Ni-Cr-Si alloy powders as the interlayer alloy respectively.The effect of the bonding temperature and holding time on the microstructure and composition distribution of the joints was studied,the isothermal solidification behavior of TLP bonding process was analyzed,and the hardness and shear properties of the joints were tested.The TLP joint using Ni-Cr-B interlayer alloy consists of three typical regions: eutectic zone,isothermal solidification zone and diffusion affected zone.Cr2B+? and Ni3B+? eutectic occur in the eutectic zone of the joint center;the isothermal solidification zone is the solid solution of ? Ni-based solid solution;M3B2 precipitates are formed in the diffusion zone.With the increasing of bonding temperature or holding time,the amount of boride decreased gradually and the width of the eutectic zone become more and more narrow;the isothermal solidification interface forward from both sides to the joint center and the width the isothermal solidification zone becomes wider and wider;the boride phases in the diffusion zone continue to grow and spread to the matrix.In order to avoid the phenomenon of initial melting,the bonding temperature and the holding time of TLP process should be selected beneath the initial melting transition boundary.With the increasing of the bonding temperature the hardness of the joint decreased obviously when the holding time was 2h.With the increasing of the holding time the hardness of the joint decreased slightly at 1200?.The increasing of the bonding temperature or the holding time can help to increase the shear strength and the fracture toughness of the joint.The shear fracture surface was brittle cleavage fracture mode at 1170 ? for 30 min.The TLP joint using Ni-Cr-Si interlayer alloy consists of two typical regions: eutectic zone and isothermal solidification zone.Ni16Cr6Si7 + ? and(Cr,Si)3Ni2Si + ? eutectic occur in the eutectic zone of the joint center;the isothermal solidification zone is the solid solution of ? Ni-based solid solution.With the increasing of bonding temperature or holding time,the width of the eutectic zone become more and more narrow and the width the isothermal solidification zone becomes wider and wider.In order to avoid the phenomenon of initial melting,the bonding temperature and the holding time of TLP process should be selected beneath the initial melting transition boundary.With the increasing of the bonding temperature the hardness of the joint decreased obviously when the holding time was 2h.With the increasing of the holding time the hardness of the joint decreased slightly at 1170?.The increasing of the bonding temperature or the holding time can help to increase the shear strength and the fracture toughness of the joints.The shear fracture surface was ductile micro-porous aggregated fracture mode at 1170 ? for 30 min.