Vacuum Brazing and Diffusion Bonding of DD6 Single Crystal Alloy

DD6,the second generation single crystal superalloy developed in China, was joined by  vacuum brazing and diffusion bonding respectively. Firstly, BNi82CrSiB was used as brazing filler metal to join DD6 at 1070°C for 15 min. Diffusion bonding of DD6 at the condition of 1050°C/50MPa/2h was also carried out by employing Ni/Al nanostructured foil as interlayer. The micro-analysis results showed that, for the two kinds of joints, the microstructure characterization of reaction layer near the bonding seam was similar. The joint properties were tested at the room temperature and 750°C. At 750°C, the tensile strength of the brazed joint reached about 400MPa, and the corresponding stress-rupture strength at the condition of 750°C/100h was 100MPa. However, the maximum shear strength for the diffusion bonded joints at room temperature was only 118MPa. Although, at present, the property of diffusion bonded joint is inferior to that of brazed joint, the process of diffusion bonding is still attractive for DD6 superalloy. This is because, when the formed joints are heated to a higher temperature again, the diffusion bonded joints using nanostructured foils will no longer melt like the traditional brazing filler metals, and it means that  diffusion bonded joints would exhibit a higher service temperature than brazed ones.