The effect of radiation induced gas on the stress rupture properties of an aluminium-lithium alloy

The changes in stress-rupture properties of an aluminium-lithium alloy induced by the presence of inert gas bubbles after neutron irradiation have been investigated in the temperature range of 175 °C to 300 °C. A bubble distribution with a mean diameter of 47 Å at an average spacing of 1400 Å produces a decrease in the minimum creep rate of two orders of magnitude below that for the bubble-free material under the same test conditions. For very fine bubble distributions and distributions which contain a narrow size range of large bubbles, a breakaway to a very high stress-sensitivity at low stresses occurs. This is absent in alloys which contain stronger bubble obstacle arrays which include a wide range of bubble sizes. All inert gas concentrations reduce creep ductility of aluminium-lithium alloy but the severity of embrittlement increases markedly with gas concentration and testing temperature. The existence of a critical bubble size for breakaway growth of grain boundary voids is implied by the experimental evidence. For a given bubble distribution a critical stress exists below which grain boundary degeneration does not occur. As the gas concentration is increased, the fracture mechanism tends increasingly towards inter-granular failure