THERMAL-STABILITY OF SMALL HE-VACANCY CLUSTERS IN 316L STAINLESS-STEEL IRRADIATED WITH 2.5 MEV HE-DEGREES-C( IONS AT 550)

In this work, temperature-variation irradiations were performed with 2 .5 MeV He+ ions in order to study thermal stability of small He-vacanc y clusters in 316L stainless steel at 550 degrees C. One specimen was irradiated at 300 degrees C to a low dose of 6 x 10(18) ions/m(2), and was subsequently irradiated at 550 degrees C to a high dose of 2.5 x 10(21) ions/m(2). For comparison, two other specimens were irradiated to the same high dose of 2.5 x 10(21) ions/m(2) at constant temperatur es of 300 degrees C and 550 degrees C, respectively. Microstructures w ere investigated with cross-section transmission electron microscopy ( XTEM) after irradiation. It is found that the pre-irradiation at 300 d egrees C increases significantly the number density of He-vacancy clus ters in the subsequent irradiation at 550 degrees C even if the dose o f the pre-irradiation is low, indicating that the small He-vacancy clu sters formed by the pre-irradiation are very stable in the subsequent irradiation at 550 degrees C, with a migration coefficient smaller tha n 1 x 10(-18) m(2)/s. (C) 1998 Elsevier Science B.V.