MECHANICAL PROPERTIES, DISLOCATION SUB-STRUCTURE AND DENSITY IN NIOBIUM SINGLE CRYSTALS DEFORMED AT HIGH STRAIN RATES

Mechanical properties of single crystals of niobium have been measured in the strain-rate range 103-104 see−1 where flow is thermally activated and is probably controlled by the Peierls stress. Dislocation configurations and densities have been measured as a function of strain at strain rates of 6·5 × 103 sec−1 and 2·7 × 10−4 sec−1. The flow stress is a square root function of the dislocation density at both strain rates and the rate of increase of dislocation density with increasing strain is independent of strain rate. It was found that the work-hardening rate decreased with increasing strain rate and the dislocation configurations observed are consistent with a work-hardening mechanism based on dislocation interactions of the type. © 1969 Taylor & Francis Group, LLC.