Vacuum brazing of TiAl alloy to 40Cr steel with Ti60Ni22Cu10Zr8 alloy foil as filler metal

Dissimilar metal vacuum brazing between TiAl alloy and 40Cr steel at 900 °C for 5 min, 10 min and 15 min was conducted with Ti-based alloy foil as the filler. Five distinct regions were detected in the brazed seam from each joint during microstructure examination. The hardness in the brazed seam was measured much higher than those in the two substrates, and the hardness in the filler metal layer was higher than that in the reaction layer. However, brazing for longer time can reduce the hardness of the brazed seam. The average shear strength of the joint was 26 MPa when the joint was brazed for 5 min, and it increased to 32 MPa when brazed for 10 min and 15 min. The specimen brazed for 5 min fractured through the interface between 40Cr steel base metal and filler metal layer, but the specimen brazed for 10 min and 15 min fractured through the filler metal layer in the brazed seam. It was found that the compositions of the filler material and sufficient interdiffusion between the filler and substrates are important to improve the joint strength, and the mechanical properties of the filler metal also control the strength of the resultant joint.