1998 Volume 47 Issue 7 Pages 706-711
In order to clarify the fatigue crack propagation characteristics at a cryogenic temperature of the equiaxed Ti-6Al-4V alloy, fatigue crack propagation tests were carried out at 77K and 298K. Microscopic observations were also made on the longitudinal section and fracture surface of specimens. The fatigue crack propagation rate at 77K was smaller than that at 298K, especially in the low propagation rate region, where the crack closure level was higher as compared to that at 298K. The crack propagation characteristics in terms of the effective stress intensity factor range at 77K and those at 298K were close to each other. A marked crack bifurcation was seen in the low propagation rate region at 77K. Transmission electron microscopic observations revealed that a high-density dislocation structure existed in the close neighbor of crack route, and cracks propagated mainly across α-grains accompanied with small branch cracks. Although the fracture surface morphologies at these two temperatures were almost the same, the plateau in the low propagation rate at 77K was smoother as compared to that at 298K.
