TWI

In relation to the development of corrosion barrier capsules for spent nuclear fuel disposal, friction stir welding experiments were conducted on oxygen-free copper plate specimens (thickness 20 mm) using different joint preparation, shielding gas and machined groove depth conditions to study the behaviour of entrapped oxide particles. The effects of oxide removal (by chemical cleaning) and use of Ar shielding gas during welding were studied on workpieces in which narrow grooves (depth 0-8 mm) were made by electric discharge machining (since it has been reported that machining the workpiece reduced the occurrence of oxide particles). Microstructure was observed by optical microscopy, SEM and electron backscatter diffraction. Hardness profiles were measured by a microhardness tester. Hydrogen sickness, which results in voids, was examined by annealing of test pieces in 90%N₂, 10%H₂, 850 deg.C, 30 minutes. The role played by local oxide particle pinning of grain boundaries during annealing in enhancing the formation of inhomogeneous microstructure is discussed.

7th International Symposium, 20-22 May 2008, 4B: Non Ferrous, Paper 01