FRACTURE MORPHOLOGIES EXHIBITED BY COMMERCIALLY PURE TITANIUM WHEN STRAINED TO FAILURE WHILE IN CONTACT WITH CHLORIDE-CONTAINING ENVIRONMENTS

The combined effects of oxygen, nitrogen and carbon, expressed as an o xygen equivalent {O}, and, also, the influence of residual iron conten t, on the stress-corrosion behaviour of commercially-pure titanium whe n strained slowly to failure while in contact with sea water have been investigated. The fracture morphologies exhibited comprised a mixture of cleaved facets and areas of low-energy ductile rupture of the alph a phase, referred to as flutes or flutings. An increase in the {O} con tent resulted in an increase in the number of cleaved facets and in th e associated continuity of the observed cleavage fracture. The cleaved facets were not exactly smooth surfaces, but were comprised of facets separated by small steps. The latter have been associated with slight differences in orientation between the cleavage planes and the crack- propagation plane. Flutings which were well developed in low residual iron-containing titanium allowed the joining of two cleavage planes in two different grains sharing a common boundary. However, when two cle avage planes were unable to join by a single-fluted system, a two-flut ed system which met at a grain boundary became operative. Increased re sidual iron levels were found to eliminate stress-corrosion susceptibi lity; hence, the non-occurrence of cleavage fracture in low {O} titani um. In high {O}-containing material, cleavage fracture was observed, b ut with a much reduced continuity of the cleavage fracture.