Research On Brazing Process And Mechanism Of TZM Alloy By Using Ti-Ni Brazing Alloys

TZM alloy had been widely used in aerospace, nuclear power and other fields,which was a kind of high temperature material with good performanc. Aiming the high temperature working environment connection requirements of TZM alloy, the brazing of TZM alloy using three kinds of TiNi eutectic brazing alloy had been realized which obtained high performance splices in this paper. The effects of brazing process on the interfacial microstructure and mechanical propertieswere studied in details, and the interface structures of brazed joints were expounded. The related factors of the dissolution of the TZM alloy had been explored, so did the fracture mechanism. The relationship among brazing alloys, mechanical properties and interfacial microstructure of joints had been analyzed comprehensively. The corrosion of TZM alloy caused by Ti was controled by increasing the content of Ni element in brazing alloy. And the best brazing process parameter was summarized at T=1240°C/t=20min using Ti-61 Ni brazing alloy.The three kinds of TiNi eutectic brazing alloy had been detected, which were prepared by vacuum arc remelting. Ti-24 Ni brazing alloy consisted of two kinds of phases: δ-Ti2 Ni phase and Tiss. The melting point of this Ti-24 Ni was about 940°C. Two phases, TiNi phase and dispersed distributed δ-Ti2 Ni phase, were detected in Ti-50 Ni brazing alloy, and the melting point was 1290°C. Ti-61 Ni brazing alloy, with a melting point at 1114 °C, was consisted of TiNi phase and TiNi3 phase.The interfacial microstructure of the joints made by using Ti-24 Ni brazing alloy was TZM/ Tiss/δ-Ti2 Ni phase/ Tiss/TZM. The brazing seam had a symmetric structure with no defects. There were some crack-like structures formed between Tiss layer and TZM substrate. This is because the liquid brazing alloy infiltrated the TZM substrate along grain boundaries and numbers of Mo blocks were dissolved into the brazing seam.Finally, the crack-like structures were retained at the brazing seam in cooling process.Analysis showed that both the thickness of Ti2 Ni phase layer and the amount of crack structureaffected the mechanical properties of joint.The brazing seam obtained by using Ti-50 Ni brazing alloy mainly contained TiNi3 phase and TiNi phase and a small amount of Ti2 Ni phase, which also had a diffusion zone. Due to the high brazing temperature, recrystallization of base metal was occurred which resulted in the easiercrystal infiltrate in base metal. The corrosion of base metal by Ti-50 Ni brazing alloy was intensified, and the brazing seam had net-like structures.The net-like structures became small and uniform when the brazing temperature was high. Fracture analysis showed that fracture positions were occurred in the center of the brazing seams, and the fracture mode was brittle fracture.The joints of TZM alloy, which were brazed with Ti-61 Ni brazing alloy, contained TiNi phase and TiNi3 phase. There were no crack-like structures or net-like structures occurred in the brazing seam, which was ascribed tothe increasing of Ni content in Ti-61 Ni brazing alloy. Some Mo matrixs were dissolved into the brazing which formed a metallurgical bonding, and the mechanical performance of joints was enhanced. The corrosion of base metal by Ti-61 Ni brazing alloy was intensified with higher brazing temperature or longer holding time. The fracture positions of all the joints were occurred in TZM alloy, the fracture mode was brittle fracture. The sequence of each interfaceproduct was ensuered by thermodynamics calculation.