Abstract
The effects of environment, microstructure and texture on transgranular fatigue crack facet orientation are established with electron-back scattered pattern analysis and stereofractography for single grains in peak aged AlLiCuZr alloy 2090. For vacuum, facets are near-{111} due to fatigue fracture through intense deformation bands with a complex planar-slip dislocation structure. Multiple facets in single grains and the tortuous crack path are caused by high shear stresses resolved on multiple slip systems. Low stress intensity range fatigue fracture in NaCl is transgranular and faceted, but not tortuous. Eighty-five per cent of the facets in unrecrystallized plate and 50% of the facets in recrystallized sheet are within 10° of a high index plane, on average {521}, subjected to high normal stresses. Such facets are inconsistent with: (a) hydrogen-enhanced localized plasticity and {111} decohesion; (b) slip-locking with bisecting {100} cracking; (c) environment-enhanced alternate slip with {100} faceting; or (d) {100}{100} decohesion. Environmental fatigue may be governed by faceted cracking associated with hydrides or hydrogen embrittled dislocation cell walls.
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