Hardening behavior of molybdenum by low energy He and D ion irradiation

Hardening of Mo by He and D ion irradiation with fusion relevant energy was examined by means of nanoindentation technique and TEM. Steep initial increase of load/displacement-displacement plots and following pop-in movement of the indenter indicate that the subsurface region where the ion-induced damage occurs is hardened. In the early stage of irradiation the hardness increases by about a factor of two due to the formation of dense dislocation loops and saturates for D ion irradiation and He ion irradiation at high temperature. For D ion irradiation, however, one order of higher displacement damage is required to cause similar hardening. In the case of He ion irradiation at 300 K the hardness increases by a factor of four at dose of 1.0 x 10(22) ions/m(2), where a high-density of He bubbles is formed. These results indicate that the irradiation effects of He are much stronger than that of D. (C) 1998 Elsevier Science B.V. All rights reserved.