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 incr ease of load/displacement-displacement plots and following pop-in movement of the indenter indicate that the subsurface region where the ion-induced d amage occurs is hardened. In the early stage of irradiation the hardness in creases 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 te mperature. For D ion irradiation, however, one order of higher displacement damage is required to cause similar hardening. In the case of He ion irrad iation 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 resu lts indicate that the irradiation effects of He are much stronger than that of D. (C) 1998 Elsevier Science B.V. All rights reserved.