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Brazing Stainless Steel to Titanium

Brazing steel to titaniumResearch Objective
To braze a stainless steel tube to a titanium “puck” without flux in a vacuum atmosphere.

Parts & Materials Description
1/8” diameter, stainless steel tube, 1 5/16” diameter, 11/16” wide titanium “puck”; braze ring

Temperature Required

Induction Heating Equipment
7.5 kW RF power supply; vacuum heating chamber; two-place, two-turn helical inductor (coil)

Operating Frequency
250 kHz

Heating Procedure
A specially-designed two-place, two-turn helical inductor was used to provide heat from either side of the braze joint. This allows the heat to soak into the joint area. Initial tests were conducted with temperature sensing paints to establish time-to-temperature and heating profiles. The parts were cleaned with acetone the braze ring was positioned over the joint area, and the assembly was placed in position with a 1/16” gap between the “puck” and the inductor. After pulling a vacuum, RF heat was applied with the power supply for 80 seconds to reach the brazing temperature of 2,000°F. At this temperature the braze alloy flowed into the joint and formed a strong bond. A 30-minute cool-down cycle is recommended before venting the vacuum chamber.

Consistent, repeatable results were achieved at 2,000°F with an 80-second heat cycle. The braze flowed cleanly around the entire diameter of the stainless steel tube. The finished assembly required no cleaning.

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