The high temperature static recovery and recrystallization behaviour of cold-worked Carrara marble

Abstract

The static recovery and recrystallization behaviour of Carrara marble has been investigated as a function of pre-strain (8–27%) and annealing temperature (500–700 °C). Quantitative estimates of the rate of recovery were obtained by comparing the stress/strain curves generated at a temperature of 426 °C, a confining pressure of 170 MPa, and a strain-rate of 3 × 10 −4s −1 before and after a period of isostatic annealing. Curves of fractional recovery ( r) as a function of log time ( t) show a characteristic sigmoidal shape in which the rate of recovery ( dr/d logt) is initially small, increases rapidly, and finally becomes small again. The acceleration of recovery occurs at shorter times both with increasing pre-strain and with increasing annealing temperature. Microstructural examination of the annealed material shows that the acceleration of recovery corresponds to the onset of recrystallization, and that prior to the onset of recrystallization, recovery is controlled by the development of a subgrain structure, whereas after recrystallization has gone to completion, it is controlled by the intensification and growth of this substructure. The results have been interpreted within the perspective of Hart's state variable description of inelastic deformation. This analysis shows that the decay of the mechanical state of the marble during annealing can be treated as a two stage static recovery process (substructure formation → substructure coarsening), with the recrystallization marking the transition between these two stages.