Description: Thermal Stir Welding (TSW) advances the more conventional Friction Stir Welding (C-FSW) process by separating the primary process variables of metal stirring and forging from the control of the workpiece temperature. The independent heating is obtained by placing an induction coil in front of a specially modified tool to bring the workpiece to the appropriate joining temperature. However, studies to date on joining of high melting temperature materials, such as nickel (Ni) based superalloys have shown high forces between the tool and workpiece, which compromise tool life. In response to this, the NASA-Marshall Space Flight Center (MSFC) has developed an advanced, subscale Ultrasonically Assisted (UA) TSW prototype. Incorporating UA into either the shoulder or pin during a FSW has shown a reduction in forces using lower melting temperature aluminum (Al) alloys. However, further work is needed to demonstrate the combined effect of UA with the TSW process for high melting temperature materials. In response to this need, Keystone is submitting this Phase I SBIR proposal to demonstrate the combined effects of UA with TSW on a Ni based superalloy of interest to the NASA.

Benefits: Potential NASA applications for the TSW technologies we propose researching and developing would be solid and liquid rocket motor casing, liquid rocket nozzle extensions, and other high temperature components; more specifically, a nozzle skirt extension for the J2X engine and 4130 steel external casing for the NASA sounding rocket.

Keystone recently completed a SBIR project funded by DARPA and ONR to develop a solid-state welding process as part of their low cost Ti alloy initiative. Keystone anticipates that as the new low cost Ti alloys become commercialized in the near future, the TSWing process will become the process of choice for joining low cost Ti alloys for a variety of markets and applications; of noteworthy interest, ONR co-funded the Keystone effort for Naval applications because of its potential to enhance Navy ship building processes.