Abstract
The thermal recovery of the increase in electrical resistivity caused by the deformation of niobium was studied. Polycrystalline niobium wires were strained in tension at temperatures from −196° to 50°C with strain rates of 3.3×10−5 to 3.3×10−3 sec−1.
The increase in electrical resistivity with strain was nearly linear and was strongly dependent upon the deformation temperature. The isochronal recovery curves of specimens revealed the well defined stage III recovery centered around 160°C and the strain aging was found at this recovery stage by the tensile test. The total recovery in this stage increased with decreasing deformation temperature and increasing strain. The effect of strain rate on this recovery was not observed apparently. The resistivities of the specimens which were stretched by 5% at each temperature and subsequently annealed up to 220°C showed a negative deviation from the initial resistivity.
It is concluded that the recovery in the stage III is mainly caused by the clustering of oxgen atoms to dislocations and the dependence of the stage III recovery on deformation temperature is attributed to the difference in the dislocation density. The experimental results suggest that the change in dislocation density with strain increases with decreasing temperature.
