Abstract
Fatigue deformation and stage I (shear mode) crack initiation in Ti-6Al-4V alloy test pieces have been studied using optical microscopy. Two types of stage I fatigue crack initiation were observed, (a) alongα/β interfaces and (b) transcrystalline initiation acrossα grains in partly transformed microstructures and acrossαβ interfaces in fully transformed microstructures. The α/β interface cracking occurred predominantly in the low stress regions of the test pieces. These observations suggested that a microstructure with a smallα grain size, to minimize the mean free slip path, and with minimum lengths ofα/β interface, would have a high fatigue strength. Such a microstructure, with anα grain size of < 10 μm, and spheroidal or near spheroidalβ particles, was produced by thermo-mechanical processing. The rotating cantilever fatigue strength of this microstructure, ± 670 MN m−2 at 10−7 cycles, compares with fatigue strengths in the range ± 480 to ± 590 MN m−2 for commercial Ti-6Al-4V bars.
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References
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Stubbington, C.A., Bowen, A.W. Improvements in the fatigue strength of Ti-6Al-4V through microstructure control. J Mater Sci 9, 941–947 (1974). https://doi.org/10.1007/BF00570387
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DOI: https://doi.org/10.1007/BF00570387