Recovery and Recrystallization in Metals examined in terms of the Restoration of the Transient Creep Properties

Pure lead wires extended by creep under identical conditions have been subjected to a period of anneal, during which the stress was removed, and then re-tested under the original creep conditions. The effect of the temperature, the time of the anneal, and the grain size on the subsequent creep properties have been examined. As far as the grain size is concerned, there appears to be very little effect until the grain diameter becomes commensurate with the specimen diameter, when the amount of recovery softening, under any particular conditions, increases. The general features of interrupted creep observed previously by the author in leads which did not recrystallize are again exhibited, in particular, the creep results can be fitted by assuming some fraction N of the material to have had its original creep properties fully restored. This fraction is now made up of both recovered, n , and recrystallized, X , material. The time function of the recovery process is the same as that observed in the non-recrystallizing leads, and it is thus possible to compute the values of n and X in any particular case. A theory of recrystallization is developed based on the concept that nuclei are formed by the recovery process; this is shown to satisfy the observations and provides an activation energy for the growth of new material of 31 000 cal mole -1 . The activation energy for recovery is found to be 19 800 cal mole -1 and that for creep 18 400 cal mole -1 . Some consequences of this approach are reviewed in the light of previous work.