Possible dislocation multiplication laws operating upto the upper yield point of covalent materials were studied in <123>-oriented Ge single crystals by using techniques of stress relaxation and transient creep testing. Unlike the case of metals, the relaxation tests revealed a linear decrease in stress with time, and inverse creep was observed. It was shown that these features were a sign of multiplication processes occurring during transient tests. Attempts were made to interpret such behaviours were presented using three dislocation multiplication laws, proposed in the literature, for metals, covalent crystals in general (based upon etch-pit experiments) and Si (based upon computer simulations). Numerical reconstruction of the transient test curves showed that the last law was less satisfactory. This was attributed to the differing stress exponents of the dislocation velocity; being close to 1 in Si and close to 2 in Ge. A realistic multiplication law was expected to consider the heterogeneity of deformation at the onset of plasticity of these crystals.

A Critical Assessment of Dislocation Multiplication Laws in Germanium. T.Kruml, C.Dupas, J.L.Martin: Acta Materialia, 2006, 54[18], 4721-9