Neutron radiation hardening of polycrystalline iron

Abstract

The dependence of the yield stress of vacuum-annealed and hydrogen-purified iron polycrystals on neutron dose and annealing temperature and the influence of these two parameters on the effect of static strain-ageing has been investigated. The radiation hardening was found to depend sensitively on the interstitial impurities N and C. This may be explained by both a nucleation of precipitation and a trapping of the impurities at radiation produced intrinsic defects. The radiation enhanced precipitation predominates in the relatively impure iron samples at low doses and may be eliminated by annealing at 190°C. The trapping becomes effective 'at higher doses or in higher purity iron. Below 400°C two recovery stages for the yield stress are observed, one between 200 and 260 "C and the other between 320 and 400 "C; these may be explained by the detrapping of N and C respectively. The static strain-ageing was found to be reduced by neutron irradiation. It reappears after annealing at temperatures at which the precipitates are thought to be redissolved and the C and N atoms to be detrapped.

Initiation and propagation of cleared channels in neutron-irradiated pure copper and a precipitation hardened CuCrZr alloy

“…The phenomenon of yield drop is commonly observed in unirradiated bcc metals (e.g. Seidel 1969) and alloys and is known to occur as a result of unlocking of dislocations from the "atmosphere" of carbon and nitrogen atoms (Cottrell and Bilby 1949). The occurrence of yield drop has been observed even in the unirradiated fcc copper containing small amounts of zinc (Ardley and Cottrell 1953).…”

Radiation effects in nuclear reactor materials—correlation with structure

“…unirradiated yield stress also ceases at about room temperature, Little (1967) inferred that thermally-activated overcoming of radiation-produced defects occur only at temperatures above which the unirradiated rate-controlling mechanism becomes athermal; in the absence of the latter, the defects introduced by irradiation would have been rate-controlling even at lower temperatures. Seidel (1969) has explained the differences in the observations on irradiation effects in polycrystals and single crystals of ~t-iron (figures 3a and b) as arising from the opposing influences of irradiation on the two parameters ai and K in the well-known Hail-Petch relationship a = tr~ + Kd-1/2 relating strength a to grain diameter d. In the unirradiated condition, the temperature dependence of flow stress is mainly contained in the Hall-Petch intercept ai. Since irradiation is found to increase the temperature dependence of the single crystal flow stress (figure 3b) it is to be inferred that the temperature dependence of ai is increased by irradiation.…”

Barkhausen and magneto-acoustic emission from ferromagnetic materials

“…Vacancies can be 'injected' into the matrix to aid dislocation recovery processes (dislocation climb, polygonization and migration into grain boundaries) from two sources: (i) The break-up of vacancy-interstitial solute complexes; and (ii) the thermal emission from cascade centres (these existing as vacancy dislocation loops or sicrovoids). The thermal dissociation of vacancy-carbon or vacancy-nitrogen atom pairs is believed to occur at ~200°-300°C (Fujita and Damask, 1964;Wutting et al, 1968;Seidel, 1969). These temperatures are significantly below the temperature range of 300°-400°C for major recovery and annealing out of radiation damage in the form of defect clusters or dislocation loops (Eyre and Bartlett, 1965).…”