Patent Number: 054901871
Section: summary

BACKGROUND OF THE INVENTION This invention relates to a method for controlling the migration and removal of gas bubbles and voids from a metal material. Nuclear reactor lifetimes are influenced by the structural damage due to gas bubbles and voids. The formation and growth of helium bubbles in metals and alloys following (n,.alpha.) reactions or .alpha. implantation are of practical interest due to the long-term deleterious effects of inert gases in fission and fusion reactor structural materials, such as reactor fuel cladding or containment structural materials. Because inert gas atoms are essentially insoluble in all metals, bubbles quickly nucleate at defects in the host lattice and subsequently grow by acquisition of additional gas atoms (and capture of vacancies to lower the gas pressure within the bubble) and by bubble migration and coalescence. In multiphase alloys, inert gas bubbles are typically found at matrix/precipitate interfaces. It is an object of this invention to provide a process whereby inert gas bubbles and voids are removed from fusion and fission reactor materials. It is another object of this invention to provide a process whereby impurity metal particles attached to the bubbles or voids are melted to provide a liquid coating to allow the bubble or void to migrate with much greater velocity than is otherwise possible. It is still a further object of this invention to provide a process for biasing the direction of migration of the bubble or void out of a metal by applying a temperature gradient across the metal. Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention. SUMMARY OF THE INVENTION To achieve the foregoing and other objects, a method is provided for biasing the direction of migration of gas bubbles or voids out of a host metal (or metal alloy), which contains impurity metal particles, by applying a temperature gradient across the host metal (or metal alloy). In the preferred embodiment of the present invention, the impurity metal particles are insoluble in the host metal and have a melting point lower than the melting point of the host material. By melting the impurity metal particles, but not the host metal, the liquid impurity metal is distributed over the surface of the inert gas bubbles or voids, thereby enhancing bubble diffusion in the host metal. Also, preferably the impurity metal is lead or indium and the host metal is aluminum or a metal alloy. Operating fusion and fission reactors can provide the required temperature gradient during normal operating conditions, thereby removing the gas bubbles or voids without interruption of operations. Alternatively, an external heating source (e.g., electrical resistance heating) can be used to provide the required temperature gradient when the reactor is off line.