SUBCRITICAL CRACK GROWTH IN SEVERAL TITANIUM ALLOYS
NAVAL RESEARCH LAB WASHINGTON DC
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Studies of low-cycle fatigue crack propagation in air and in salt water environments and salt water stress-corrosion cracking SCC were conducted on several intermediate-to-high strength, very low interstitial oxygen, titanium alloy plate materials. The alloys studied included one sample each of Ti-7Al- 2Cb-1Ta and Ti-7Al-2.5Mo, and two samples each of Ti-6Al-4V and Ti-6Al-6V-2Sn. The yield strengths of these alloys ranged from 110 to 150 ksi 77.3 to 105.5 kgfsq mm and included both as-received and heat-treated conditions. Fatigue and SCC data were obtained from single-edge-notched SEN cantilever specimens, and the results were analyzed in terms of crack tip stress-intensity parameters. Most of the alloys investigated exhibited low resistance to low-cycle fatigue crack propagation. The most favorable results were obtained from the Ti-6Al-4V alloys. However, several alloys were highly resistant to environmentally- accelerated crack growth in salt water. Several alloys also showed a correlation between fatigue crack growth behavior in salt water and the threshold stress- intensity for SCC to occur K sub Iscc. Examination of fatigue surfaces by electron fractography revealed that the predominant mode of separation was microvoid coalescence, regardless of environment.
- Properties of Metals and Alloys