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Abstract
Dynamical fracture experiments with plasma hydrogenation have been used to study the influence of hydrogen on the brittle-to-ductile transition (BDT) in dislocation-free Czochralski-grown single crystals. The results show no effect of hydrogen on the surface energy of silicon, but the BDT temperature is lowered by about 60 K and the BDT activation energy by 0·8 eV. Also the threshold stress intensity for dislocations to be emitted from a crack tip is lowered by 0·2 M Pa m1/2. The Haasen model of the BDT is modified to contain a frictional or starting stress which is decreased by hydrogen. Possible reasons for the hydrogen softening are discussed.