Abstract
The hydrogen embrittlement of L1 2-type Co 3Ti compounds was investigated by the deformation and fracture experiments using the “bulk” specimens and the “thin” specimens for TEM observation in both forms of polycrystals and single crystals. The mechanical behavior for the “bulk” specimens was strongly sensitive to the environmental gas, the strain rate and the hydrogen gas pressure, regardless of polycrystals or single crystals. In the most embrittled state, the polycrystals showed the intergranular fracture mode and the single crystals did the cleavage-like fracture mode. TEM observations for the “thin” specimens exhibited that the specimens tensile-tested in vacuum showed extensive generations and propagations of the dislocations from a propagating micro crack while the specimens tensile-tested in hydrogen gas did show the extensive introductions of stacking faults together with dislocations along the either side of the cracked surfaces. This microstructural feature was investigated in both forms of polycrystalline and single crystalline. As micro mechanism of hydrogen embrittlement for the Co 3Ti compounds, it was suggested that hydrogen accumulated at a tip of propagating micro crack introduced the stacking faults, hindered the emissions and motions of dislocations and thereby resulted in decreasing the associated plastic works.
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