RESISTANCE WELDING OF REFRACTORY METALS.
Final technical rept. Aug 64-Feb 67,
TRW EQUIPMENT LABS CLEVELAND OH
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The purpose of this program was to determine the causes of electrode sticking when resistance spot welding refractory metals Cb 752, Ta-10W, TZM, D-43, and T-222 and to investigate means of eliminating it. Also, a limited investigation was conducted on Cb-752 and Ta-10W alloys to determine the feasibility of welding coated refractory metals. Electrode sticking to resistance spot welded refractory metal alloys was found to be caused by a combination of brazing, solid-state bonding and mechanical bonding depending on the temperatures achieved at the interface between the work and electrodes. The temperatures at the electrode-work interface were generally within the recrystallization range of the copper electrode and often above the melting point of the electrode. Electrode sticking was found to be directly related to welding current, electrode force and weld time. Class 1 copper electrodes were found to be generally less susceptible to sticking than class 3, class 11 or pure molybdenum because of its superior electrical and thermal conductivity. Several methods aimed at reducing electrode sticking were evaluated. Cryogenic welding, solid state welding and projection welding were found to provide the greatest relief from electrode sticking. Projection welding utilizing a solid state bond was considered to have more promise than cryogenic welding, and to provide better strenth properties than conventional solid state bonds made by resistance welding.
- Fabrication Metallurgy