INITIATION AND PROPAGATION OF STRESS-CORROSION CRACK IN ALPHA-TITANIUM ALLOYS AS CANDIDATE CONTAINER MATERIALS FOR THE HLW DISPOSAL

摘要

Initiation and propagation behavior of stress-corrosion crack is investigated in the present investigation for alpha-phase titanium (Ti) alloys exposed to environments of an electrode potential region suitable to hydrogen-evolution. The following conclusions were obtained; a definite correlation was found to exist clearly between the formation of Ti-hydride layers and the crack initiation based on microscopic observation conducted, a layer of hydride started to grow from the surface to the inside of a specimen, when the thickness of the hydride layer reached a critical value, the hydride layer fractured mechanically, then, a new layer of hydride started to grow at the tip of the crack, the newly formed hydride layer started to fracture mechanically after it had reached the critical thickness, and [6] the stress-corrosion crack propagated according to the sequence described above. Based on the data obtained on the critical thickness of hydride layers to initiate fracturing and on the time dependency of the rate of hydrogen evolution, alpha-Ti alloys are concluded to be resistant to stress-corrosion cracking damages in the coming 1,000 years under the anticipated environments that overpack materials for disposing of high-level waste will be exposed.