Fatigue fracture and slip processes in B.C.C. TiV alloy single crystals

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The fatigue crack propagation behavior of oriented beta-phase (b.c.c.) Ti-40 at.% V alloy single crystals as well as polycrystals has been studied. Both the fatigue limits and the crack propagation rates are dependent on the crystallographic orientation of the specimens. Extensive cracking on a plane inclined to the stress axis is observed in crystals with the specimen axis near the [110] direction. Crack propagation in these samples as well as in those with specimen axis near the [111] direction and in the polycrystalline specimens obey the relationship da dN α ΔK1.8. An examination of the features of the fracture surfaces in terms of the slip processes at the crack tip indicate that ductile fatigue crack growth occurs by slip on intersecting slip planes and that the crack plane contains the line of intersection of at least two active slip planes. Macroscopic crack growth on an inclined plane can occur as a consequence of unequal slip on two intersecting slip planes. These observations as well as calculations based on both Isotropie and anisotropic plasticity strongly support ductile fatigue crack growth being controlled by crack tip opening displacements. Crack tip yielding models based on diffuse as well as discrete slip are used to analyze the results. © 1978.

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Acta Metallurgica