Martensitic transformation and mechanical deformation of high-purity lithium

The martensitic transformation of Li is characterized by a large temperature hysteresis and a complex low-temperature phase diagram. The phase transition is very sensitive to small mechanical strains. On the other hand, within the hysteresis region peculiar mechanical properties are observed. The critical resolved shear stress exhibits a pronounced anisotropy and asymmetry between tension and compression while the strong temperature dependence typical for other b.c.c. metals is absent. Investigations of the plasticity of Li single crystals above the Ms temperature indicated that stress-induced nuclei of the low temperature phase interact with the glide dislocations. This was partially confirmed by in situ deformation experiments during neutron scattering and seems to be in agreement with recent theoretical approaches which predict a stabilization of martensite clusters in the nucleation state above the Ms temperature.