Strength of high temperature brazed joints:influence of brazing parameters

Investigations on strength of brazed joints in AISI Types 321 and 316 Ti stainless steel made with two metallurgically different high temperature filler metals (BAu-4 and BNi-5) demonstrated the influence of important brazing parameters. Using the AWS single-lap standard test method, several parameters-brazing cycle, condition (roughness) of the brazing surface, fixed and free-adjusting clearance - were varied. With the brittle phase, tests with filler metal BNi-5 showed that too short a brazing time and brazing surface conditions hindering filler metal flow give an average unit tensile stress in the base metal at failure which is similar to the 0.2% yield strength of the base metal. The strength of joints brazed with the ductile gold-nickel filler metal BAu-4 is by no means influenced by the roughness of the surface as much as it is by the nickel-base filler metal. Comparing investigations on joints with a fixed and free-adjusting clearance shows that, in the case of the free-adjusting clearance, the average unit tensile stress in the base metal at failure is about 10% lower. Investigations demonstrated that, using applicable brazing parameters even at over-lap-to-thickness ratios of 1.5-2, joints brazed with both filler metals failed in the base metal.