Thermocouple Application Note 8
How to Weld Tungsten-Rhenium Thermocouple Wire
Joining of tungsten and tungsten-rhenium alloys has been done using a variety of techniques from gas welding to ultrasonic welding. However, for joining wires to produce thermocouple junctions the most common technique is gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding. An experienced welder can easily join the small diameter wires normally used for thermocouples without the use of filler metals or fluxes.
After TIG welding the thermocouple bead and some of the adjacent material may be quite brittle due to the cast structure of the fused metal. Therefore it is often advisable to wrap the wire ends together before welding using a small diameter wire of either alloy to provide support. In some designs such support may be possible by wrapping the negative thermoelement leg (the high rhenium content alloy is more ductile) around the positive leg.
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