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    Fractographic Analysis of Hydrogen-Assisted Cracking in Alpha-Beta Titanium Alloys

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    The role of hydrogen in the subcritical crack growth of titanium alloys is a subject of intense interest to those who use these alloys for structural applications. The most widely accepted theories are based on the absorption of hydrogen (in the case of environmental hydrogen-assisted cracking), its diffusion to regions of high tensile stress, and the initiation of microcracks at hydrides precipitated in such regions. One of the difficulties with such a mechanism is the paucity of observations of titanium hydrides on fracture surfaces, such as those caused by stress corrosion cracking or inert-environment sustained load cracking caused by residual hydrogen impurity. Another difficulty has been the identity in microstructural crack paths between stress corrosion cracking in hydrogen-containing (saltwater, etc.) and hydrogen-free (carbon tetrachloride) environments.

    Studies reported in this paper suggest that hydrogen is not unique in its ability to cause alpha cleavage, but may be a primary cause of alpha-beta interface cracking. Alpha cleavage also occurs in sustained load cracking, but is not, in the present studies, influenced by hydrogen content. Cracking in environmental hydrogen gas is primarily distinguished by alpha-beta interface cracking. The detailed fractographic character of such interface cracking appears to show that the microstructural locus of interface cracking is at the boundary between the alpha phase and the interface phase. The existence of this phase in bulk materials has recently been called into question, and it will be one purpose of this paper to discuss the role of hydrogen content on its formation and the effects of this phase on fracture mechanisms.


    subcritical cracking, fractography, stress corrosion cracking, hydrogen embrittlement, titanium alloys, mechanical properties, fracture (materials), cracking mechanisms

    Author Information:

    Meyn, DA
    U.S. Naval Research Laboratory, Washington, DC

    Bayles, RA
    U.S. Naval Research Laboratory, Washington, DC

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP25631S