Small specimen procedures for determination of deformation maps

Irradiation-hardened metals undergo changes in plastic deformation modes that degrade mechanical properties. Variation of deformation mode as a function of fluence and level of strain can be tracked with deformation mode maps. Mapping requires many tensile tests and TEM specimens. To streamline the process, a special tensile test cradle and refined TEM specimen preparation techniques have been developed. The 0.25-mm-thick sheet tensile specimen with dogbone shape is sufficient to ensure bulk mechanical behavior and eliminates grinding operations for the TEM pieces. Extraneous strains that might arise in such a small specimen from pin loading or friction gripping are avoided by loading the specimen under its shoulders in a small, sliding cradle which also prevents accidental damage during remote handling in and out of the tensile machine. After straining, three TEM pieces each 1.5 mm square are cut from the gauge section in one pass in a special jig using a slow speed rotary saw fitted with ganged blades. To accommodate these square specimens during electrochemical thinning, the specimen holder is custom altered. Finally, for TEM examination, the thinned specimen is supported by an auxiliary platform constructed from molybdenum foil rings.