Description of low-temperature interstitial hardening of the b.c.c. lattice from in situ experiments

The interactions between mobile screw dislocations and interstitial atoms are described by analogy with interactions between dislocations and localized obstacles observed by in situ straining experiments on b.c.c. crystals at low temperatures. The major effect of interstitial doping is to reduce the length of the elementary screw dislocation segments on which double-kink nucleation takes place. This length is evaluated using simple statistical arguments and is introduced into the strain-rate equation of the deformation. Numerical evaluation of the thermal component of interstitial hardening is discussed with regard to recently published data on nitrogen-doped ultra-pure niobium. Difficulties associated with the experimental determination of interstitial hardening by conventional tensile tests are discussed. (author)