The effects of 100 keV He-ion irradiation on the early stage of plastic deformation of copper polycrystals were studied by examining dose-dependence of the yield stress at 77 K and slip behavior at 90 K, and ultra-micro hardness measurements on thin surface damaged layers were also carried out at room temperature. The yield stress increased slightly at a dose of 2 × 1021 ions/m2, but did not increased at 2 × 1019 ions/m2. The hardness increased markedly at 2 × 1021 ions/m2 and slightly at 2 × 1019 ions/m2. The slip behavior was markedly different between unirradiated surfaces and irradiated ones at a higher dose, and slightly at a lower dose. These facts show that the very thin surface damaged layer affects the mechanical properties of fcc bulk materials. The possibility of the use of ultra-micro hardness testing in He irradiation effects is also briefly discussed.
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