Low-Force Friction Surfacing for Crack Repair in 304L Stainless Steel

The objective of this research is to evaluate low-force friction surfacing as a means for repairing cracks in 304L stainless steel canisters. The motivation for reducing process forces is to allow for portability and miniaturization of the system to perform in-field repairs in confined spaces. 304L austenitic stainless steel rod was deposited over a substrate of the same alloy using a CNC machine tool in position control mode while observing the process forces on the back side of the repair. Friction surfacing was performed at spindle speeds up to 20,000 rpm. A fine grain structure was observed in the plastically deformed material. Axial pressures measured during the process showed a significant reduction when tests were performed at 20,000 rpm as compared to lower speeds. Friction surfacing was performed on simulated cracks followed by helium leak testing to evaluate the ability to create an acceptable repair. Closing of cracks near the interface of the substrate and deposit was observed after microstructural analyses. Acceptable helium leak rates through the repair can be achieved.