Hydrogen-induced cleavage fracture of Fe3Al-based intermetallics |
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Authors: | X Mao L Qiao |
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Affiliation: | (1) the Department of Mechanical Engineering, The University of Calgary, T2N 1N4 Calgary, AB, Canada |
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Abstract: | Hydrogen-induced fracture of ductile Fe3Al-based intermetallics was studied through mechanical testing, fracture surface observation, andin situ transmission electron microscopy (TEM) tests of tensile specimens. Mechanical properties of ordinary ductile X-80 pipeline
steel (low-alloy steel) were tested and compared with Fe3Al intermetallics. Elongations of the Fe3Al alloy decreased from 14 to 10 pct, with increases in the strain rate from 10−6 to 10−3/s. The elongation reduction of Fe3Al was caused by the hydrogen-induced fracture. There was no elongation reduction when the testing was done in mineral oil.
Non-necking occurred near the fracture section, and the fracture surfaces mainly consist of cleavage and partial intergranular
morphologies. Elongation near the fracture surface of the Fe3Al intermetallics was about 14 pct, which is the same as the total elongation. For the pipeline steel, however, an elongation
near the fracture cross section was greater than 130 pct, which was much higher than its total elongation of 17 pct.In situ TEM observation on a tensile test sample showed crack propagation accompanied by dislocation plasticity. When the Fe3Al was precharged cathodically, the crack tip was sharp. Its radius was much less than that obtained without hydrogen charging.
The crack propagated along the grain boundary for the charged specimens, but penetrated the grain boundary for the specimen
without hydrogen charging. Effects of hydrogen on plastic deformation and grain-boundary cracking are discussed in this article. |
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