Q: I’m working with a high temperature, bi-metallic bolted flange design. The steady state temperature of the flange is 1400 degrees F. The bolt is TZM, which has a lesser CTE than the thru-hole material. I’m looking for a material with a CTE less than TZM to use as a washer under the bolt head that will balance out the overall flange & bolt CTEs, to prevent overstressing the bolt at temperature. Any suggestions?
A: Probably the best bet is commercially pure tungsten. A Tungsten bolt has a melting point of 3420°C . The high temperature stability of tungsten fasteners make them ideal for some of the hottest vacuum furnace environments and will have a CTE of 4.2 10-6 (m/m-K) as long as they are in an inert or vacuum environment.