INFLUENCE OF HIGH-DOSE NEUTRON-IRRADIATION AT 385-DEGREES-C AND 750-DEGREES-C ON THE MICROHARDNESS OF MGAL2O4 SPINEL

High-purity specimens of stoichiometric MgAl2O4 single crystal spinel and a hot-pressed polycrystalline ceramic spinel were irradiated to ex posures as large as 24.9 x 10(22) n Cm-2 (E > 0.1 MeV) in FFTF at 385 and 750 degrees C. The specimens did not develop any brittleness or fr agility, and maintained their physical integrity. Microhardness measur ements revealed that initially all specimens hardened a small amount a nd then recovered slightly. At the lower irradiation temperature, the dependence of microhardness on orientation observed prior to irradiati on tended to disappear. There was also some evidence that a secondary slip system was being activated. Following 750 degrees C irradiation, the orientation dependence was not lost, and the evidence for activati on of a secondary slip system was stronger.