MICROPROBE STUDY OF BRAZED JOINT FOR SNAP 10A THERMOELECTRIC PUMP APPLICATION

There is a program requirement to produce sound brazed joints between stainiess steel and copper metal components that will remain sound after long time exposure to a high vacuum environment at a temperature of approximately 1000 deg F. Results are described of a microprobe study of one of the promising brazed joints after long time exposure to high vacuum conditions at a temperature of approximately 1200 deg F. It was desired to determine the extent of gold diffusion into the stainless steel after long time exposure under accelerated conditions. The brazing test alloy contained 81.5% gold, 15.5% copper, and 3.0% nickel. Microprobe scan photographs are shown for each of the major elements present in the test specimen and a traverse profile sketch of the braze zone is shown for the microprobe equipment set to detect gold and nickel. The results of this microprobe study indicated significant diffusion of gold into the copper metal but no diffusion of gold into the stainless steel. There were indications of minor diffusion of nickel into the copper and perhaps some concentrating of nickel atoms at the surface of the stainless steel. (auth