Ti-Cu-Ni-Nb-Al-Zr-Hf非晶钎料合金真空钎焊Ti50Al50 接头的界面组织与剪切强度

Interfacial Microstructure and Shear Strength of Ti50Al50 Joint Vacuum Brazed with Ti-Cu-Ni-Nb-Al-Zr-Hf Amorphous Filler Alloy

摘要:

在钎焊温度1140~1220 ℃、钎焊时间30 min的工艺参数下，采用Ti-9.5Cu-8Ni-8Nb-7Al-2.5Zr-1.8Hf（质量分数，%）非晶钎料成功实现了Ti₅₀Al₅₀ (at%)合金的真空钎焊连接，并研究了钎焊温度对钎焊接头的显微组织、剪切强度的影响规律。结果表明，在任何钎焊温度下获得的Ti₅₀Al₅₀钎焊接头均有3个界面反应层且每个反应层都含有α₂-Ti₃Al和Ti₂Cu(Ni) 2个物相。随着钎焊温度的增加，α₂-Ti₃Al和Ti₂Cu(Ni)在钎焊接头中的尺寸与分布发生了明显的变化，尤其是等温凝固层Ⅱ中的Ti₂Cu(Ni)相。1200 ℃下稳定存在的连续α₂-Ti₃Al层Ⅰ对母材和钎料原子的相互扩散具有阻隔壁垒作用，温度一旦超过1200 ℃，α₂-Ti₃Al相变得不稳定使得连续α₂-Ti₃Al层被打破从而失去阻隔壁垒效应。在钎缝中析出且弥散分布的α₂-Ti₃Al对焊缝中物相的形成可以起到抑制形核和细化晶粒的作用。随着钎焊温度升高，Ti₅₀Al₅₀钎焊接头平均抗剪切强度先增加后减小，在钎焊温度1180 ℃、钎焊时间30 min时钎焊接头的抗剪切强度最大，达184 MPa。剪切断口表面呈典型解理断裂特征且α₂-Ti₃Al占绝大多数。

Abstract:

Amorphous Ti-9.5Cu-8Ni-8Nb-7Al-2.5Zr-1.8Hf (wt%) filler alloy was employed to vacuum braze Ti₅₀Al₅₀ (at%) alloy at the brazing temperatures ranging from 1140 to 1220 °C for 30 min. The effect of brazing temperature on the microstructure and shear strength of the brazed joints was investigated. Results show that all the brazed joints are mainly divided into three reaction layers regardless of the brazing temperature, and both of α₂-Ti₃Al and Ti₂Cu(Ni) phases exist in each reaction layer, but their size and distribution change significantly with brazing temperature, especially the Ti₂Cu(Ni) phase in isothermal solidification layer Ⅱ. The continuous α₂-Ti₃Al layer Ⅰ is stable below 1200 °C but breaks and loses its barrier effect above 1200 °C. It is notable that the α₂-Ti₃Al precipitated in the brazed seam can act as a nucleation inhibitor and refine the crystal grain. Shear test results show that the average shear strength of Ti₅₀Al₅₀ brazed joints first increases and then decreases with brazing temperature and the maximum shear strength of 184 MPa is obtained at 1180 °C. α₂-Ti₃Al mainly occupies the fracture surface with cleavage characteristics.