A method to study deformation mechanisms in ion-irradiated steels using a disk bend test technique

A disk bend test technique has been developed for transmission electron microscopy (TEM) disks to study deformation mechanisms in ion-irradiated steels. In the bend test, a TEM disk specimen is clamped in a circular holder and indented with a tungsten carbide (WC) ball of 1 mm diameter. Models for evaluating the stress and strain components in the central region of the TEM disks were developed and used to calculate average plastic strain, surface plastic strain, and stress components at top and bottom surfaces of a 316LN stainless steel disk. Deformation regimes and stress state in the disk bend deformation were discussed in relation to the variations of strains and stresses. To investigate deformation mechanisms in irradiated 316LN stainless steel, irradiations of TEM disks were carried out with 0.36 MeV He⁺ ions and/or 3.5 MeV Fe⁺ ions at 200°C. Those irradiated samples were deformed up to a surface plastic strain of about 10% in the disk bend jig. To examine the deformation microstructures at the peak damage region, the surface layer to a depth of about 600 nm was removed from the irradiated surface by electrochemical polishing followed by back thinning to perforation. Microstructures were examined in a Philips CM 12 transmission electron microscope at an acceleration voltage of 120 keV. The results displayed changes in deformation mechanism due to ion irradiations.