Ultra-fine grained molybdenum alloys with fine TiC particles at grain boundaries that were recently developed by the authors are very promising for the application to divertor components in advanced fusion devices. In order to examine the impact toughness and microstructural change of the alloys which were exposed to high temperature heating, miniaturized flat specimens, 1 mm by 1 mm by 20 mm, of both the alloys with TiC additions to 1.0 wt% and TZM alloy were subjected to vacuum heating up to 2273 K for 3.6 ks. The impact toughness was evaluated by three-point bending tests. It is shown that the developed alloys exhibit much improved toughness (lower ductile-to-brittle transition temperature and higher yield and maximum strengths) and the toughness increases both by increasing TiC content and by using mechanical alloying (MA) treatment for fabrication : the ductile-to-brittle transition temperature of the MA treated alloy with 1 wt% TiC is 75 K lower than that of TZM. In addition, the alloy with 1 wt% TiC shows no significant grain growth, though TEM observation indicate the occurrence of recrystallization
