FRACTOGRAPHIC ANALYSIS OF TI-7AL-2CB-1TA AND TI-6AL-4V FRACTURES DEVELOPED IN 'WET' FATIGUE.
NAVAL RESEARCH LAB WASHINGTON D C
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Crack-growth-rate studies on Ti-7Al-2Cb-1Ta and Ti-6Al-4V alloys in low-cycle fatigue were performed in air and in a 3.5-percent salt-water solution. The Ti-7Al-2Cb-1Ta alloy was additionally tested in distilled water. An increase in crack-growth rate at all strain ranges was observed for the Ti-7Al-2Cb-1Ta in the wet environments over that in the dry, whereas the Ti-6Al-4V alloys did not appear to be sensitive to a wet environment. At a strain range of 8000 to 9000 microinchesinch, corresponding to about 60-percent yield strength, the crack-growth rate of Ti-7Al-2Cb-1Ta alloy accelerated and became erratic. Fractographic studies show that the increase in crack-growth rate is due to a change from the ductile mode of fatigue fracture usually found in dry low-cycle fatigue tests of titanium alloys, to the brittle quasi-cleavage mode of fracture-a fracture mechanism of stress-corrosion cracking. The amount of quasi-cleavage seen on the fatigued fracture surface generally corresponds to the crack-growth-rate increase thus, it is indicative of the degree of stress-corrosion cracking sensitivity. Author
- Properties of Metals and Alloys