Effect of Brazing Clearance on Microstructure and Properties of Vacuum Brazing Lap Joint of Ni-Based Alloys

Nickel-based alloys GH738 and GH4169 were joined using Ni-based filler BNi-2 at brazing temperature of 1 080℃with different brazing clearances.The effect of brazing clearance on the microstructure, composition distribution and micro-hardness distribution of the Ni-based alloy joint was investigated by means of optical microscopy,scanning electron microscopy with energy dispersive X-ray spectrometer and micro-hardness tester.The results show that the brazed joints in brazed seam with different brazing clearances were all composed of solid solution in both sides and intermetallics in the center.The micro-hardness of the brazed joints in the middle was higher than that in the sides.With the decrease of brazing clearance,the diffusion reactions of the filler and the base metal were more full,that could decrease the content of intermetallics in the brazing clearance.The more the content of solid solution,the lower the hardness of joint.When the brazing clearance was 30μm,the microstructure of the jiont was solid solution.