X-ray observation on fatigue failure of aluminum in air and vacuum

Fatigue failure mode of aluminum was inspected by using the X-ray diffraction technique. The specimens of aluminum single crystal were cycled under the reverse plane bending in air and vacuum. The diffraction profiles show that the Laue spots are segmented into several subspots as the stress cycling proceeds and extended gradually to the radial direction in air and to the circumferential direction in vacuum. The pseudo-Kossel patterns indicate that the diffraction profiles disappear little by little as the fatigue proceeds, and that a few lines in the air-tested specimen remain clearly to the final stage of failure, while all of them in the vacuum-tested one disappear. It is found that the pseudo-Kossel lines disappear gradually in following order of (333), (511), (422), (420)..., This phenomena are believed to be closely related to the slip characteristics of crystal. The difference of slipping modes in air and vacuum may suggest that the oxide layer grown on the surface during fatigue acts as the barrier to the slip motion of crystal in air. (author)