CHARACTERIZATION OF THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF LIQUID PHASE DIFFUSION BONDS USING EUTECTIC Ni-Hf AND Ni-Zr BRAZE ALLOYS AFTER SHORT PROCESSING TIMES (40 MINUTES)

As shown in the preceding chapter, simple binary eutectic Ni-Hf and Ni-Zr braze alloys can be used to successfully join In738 Ni-base superalloy. The joint gap must, however, be narrow (less than 0.15 mm in width) to allow capillary action to draw the filler metal into the joint. Such narrow joint gaps are usually only found in the manufacturing industry. In the repair industry, especially in IGT (industrial gas turbine) engine components, cracks are frequently wider than 0.15 mm and the simple eutectic Ni-Hf and Ni-Zr brazes will most likely not deliver adequate mechanical properties if used independently. In order to improve the mechanical properties of the In738 braze joints, the Ni-Hf or Ni-Zr eutectic braze alloy was mixed with MarM247 Ni-base superalloy powder, and processed using the liquid phase diffusion bonding (LPDB) process described in §1.6 of the literature survey.