Work-hardening behaviour of Mg single crystals oriented for basal slip

Abstract

Work-hardening behaviour of Mg single crystals oriented for basal slip was studied by means of tensile tests carried out at 4, 78 and 295 K. The crystals show critical resolved shear stress values (CRSS) for a {0001} basal slip system in the range 1–1.5 MPa. The samples exhibit two-stage work hardening characteristics consisting of a long easy glide stage and a stage of rapid hardening terminated by failure. The onset of the plastic flow up to the point of fracture is accompanied by a low work-hardening rate in the range 5 × 10⁻⁵–5 × 10⁻⁴ µ, corresponding to the hardening rate in Stage I of copper single crystals. The analysis of thermally activated glide parameters suggests that forest interactions are rate-controlling processes. The very low value of the activation distance found at 4 K, ∼0.047 b, is attributed to zero-point energy effects. The failure of crystals occurs well before their hardening capacity is exhausted by mechanisms which are characteristic of deformation temperature.

Keywords:

• magnesium
• single crystals
• plastic deformation
• basal slip
• work hardening
• fracture
• low temperatures

Acknowledgements

The financial support of Natural Sciences and Engineering Research Council (Canada) is gratefully acknowledged.