抄録
Fractographic inspections have been conducted to know the failure mechanism of a aluminum which was subjected to stress cycling under the pressure range from the ambient pressure to 10-5 Torr. The topography of fracture surface has been examined by an optical and electron microscopy, and the chemical state and/or its properties have been analyzed by using ESCA and X-ray microanalyzer. The deterioration of fatigue strength in air has been discussed on the basis of the mechanisms of chemical and physical adsorption of the constituent gas in air to the fresh crack surface.
The fracture surface appearance photographed by camera has shown that its morphology of specimen tested in air was very rugged, while it was relatively smooth in high vacuum pressure level over 10-3Torr. The dark deposits were observed on the fracture surface of the air-tested specimen, but not on the vacuum-tested one. The surface inspections by an X-ray microanalyzer indicated that the amount of oxygen molecules adsorbed on the fracture surface changed drastically in the region of 10-2 to 10-3Torr. The analytical survey by ESCA showed a marked signal of chemical shift from aluminum metal to aluminum oxide in the air-tested specimen, but not so in the vacuum tested one. These physico-chemical effects may have a great influence on the degradation of fatigue strength of aluminum in air.
