The dependence of the tensile properties of irradiated aluminium-lithium alloys upon gas bubble size and distribution

Abstract

The effect of inert gas bubbles on the tensile properties of neutron irradiated aluminium-lithium alloys was examined in the temperature range 103 to 523 °K. An analysis of the macroyield strength of alloys containing various size distributions of gas bubbles at 223 °K showed that bubbles are weak obstacles to dislocation movement with breaking angles which vary from 132° for 150 Å diameter bubbles to 144° for 50 Å bubbles. Below 50 Å diameter the breaking angle decreases rapidly and becomes 174° for bubbles approximately 15 Å in diameter. The temperature dependence of the macro-yield stress for alloys irradiated to thermal neutron doses of 1.2 × 10 19 nvt and less showed that the presence of small bubbles caused an additional friction stress. Higher irradiation doses produced dislocation locking, possible due to the formation of jogs on glide dislocations. Ductility was severely reduced at high temperatures by the presence of inert gas bubbles in the grain boundaries. The ductility of irradiated material at low temperatures increased significantly and material which contained bubbles became more ductile than the unirradiated alloy. During post-irradiation annealing, which results in the coarsening of an originally fine distribution of small bubbles, the macro-yield stress increases to a maximum value and then decreases.