Corrosion Fatigue Properties of Ti-6Al-6V-2Sn (STOA)

Abstract

The corrosion fatigue crack properties of Ti-6Al-6V-2Sn (STOA) were studied in room-temperature laboratory air, dry air, high-humidity air, and 3.5 percent sodium-chloride solution environments. The alloy was characterized by chemical, microstructural, tensile, and fracture-toughness properties. Corrosion fatigue tests were conducted using wedge-open load (WOL), center-cracked-through (CCT) and part-through-cracked (PTC) specimens. Frequency and environmental interactions were studied as well as the effects of orientation and stress ratio. The effect of frequency was to increase the fatigue crack growth rate as the frequency was decreased. A severe effect of frequency was noted in salt water where at 0.1 Hz, crack-growth rates increased to such a high level that failure occurred at Kmax levels significantly below the stress-corrosion cracking threshold. Fractographic studies showed no apparent cause of this unexpected phenomenon.