Hydrogen Embrittlement-Hydride Fracture.
ILLINOIS UNIV AT URBANA-CHAMPAIGN DEPT OF METALLURGY AND MINING ENGINEERING
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Consideration is given to causes for the extreme brittleness observed for most hydrides. Surface energies for cleavage of the beta NbH0.82 f.c. orthorhombic hydride along the 100 and 110 are obtained using fracture mechanics methods. The values are shown to be about equal to those of b.c.c. niobium. The relative surface energies of niobium and NbH are consistent with measurements of phonon frequencies and elastic constants. None of the data indicates any decrease of atomic bonding due to the incorporation of hydrogen in the metal lattice. Dislocation mobility is considered on the basis of T.E.M observations and the crystal structure. It is shown that half of the 110 111 slip systems cause hydrogen disordering and therefore experience a high lattice frictional stress. Domain boundaries also are shown to be dislocation barriers. Hydride brittleness is considered to result from the decrease in dislocation mobility and in the slip systems available to cause plastic blunting at elastic discontinuities. Author
- Metallurgy and Metallography