MIGRATION MECHANISM OF SELF-INTERSTITIAL ATOMS IN MO AFTER LOW-TEMPERATURE IRRADIATION .2. DISLOCATION PINNING

Dislocation pinning due to (110) self-interstitial atoms (SIAs) in Mo after 20 MeV proton irradiation at 5 K was investigated in the wide ra nge of Frenkel-pair concentrations C-FP from 10(-4) to 10 ppm, where d islocation pinning due to the free migration of SIAs is observed as a broad pinning at around 40 K (the so-called 40 K pinning). With increa sing C-FP, the magnitude of the 40 K pinning increases showing a shift to lower temperatures. Close study suggests that the 40 K pinning is composed of a constituent lower temperature pinning (LTP) and higher t emperature pinning (HTP). The fractional ratio of SIAs arriving for LT P to those for the whole 40 K pinning F-LTP increases with decreasing C-FP, showing saturation at 100% for C-FP below 0.001 ppm, or decrease s in proportion to C-FP(1/3) for C(FP)greater than or equal to 0.001 p pm. The C-FP dependence of F-LTP is very similar to the fractional rat io of SIA-Is in C-FP reported in Part I, where SIA-Is are (110) SIAs w hich can undergo three-dimensional migration. The C-FP dependence of S LAs of another type responsible for HTP is very similar to that of SIA -IIs reported in Part I which reveal no relaxation peak, suggesting th at SIA-IIs cannot undergo three-dimensional migration but migrate two or one dimensionally. The present work suggests that (110) SIAs of two types can be formed in Mo during low temperature irradiation.