The Metal Physics group, led by Dr. Teresa Pérez-Prado, has succeeded in stabilizing a Li phase with a hexagonal closed packed (hcp) structure at room temperature and 1 atm by the application of pressure to Mg-Li alloys. At atmospheric pressure, pure Li and Li-Mg alloys undergo a bcc to hcp transformation when cooled down to temperatures lower than about 70-80 K. Subsequent heating gives rise to the back transformation, which takes place at higher temperatures (for example, at 150 K in a Li-10%Mg alloy) as it has significant hysteresis. This study, carried out by Dr. Bonta Srinivasa Rao, a postdoctoral researcher in the group, constitutes the first time that an hcp-Li phase is stabilized at room temperature and atmospheric pressure.
The stabilization of this metastable phase is carried out by high pressure torsion. An increase in the applied pressure leads to a larger volume fraction of metastable phases. It has been observed that the transformation takes place in single phase bcc Mg alloys with a high Li content. Lowering the amount of Li results in dual hcp-bcc microstructures which do not undergo the reported transformation.
It is expected that the application of pressure, or pressure and shear straining, may lead to the development of novel metalic materials, thus widening their property range.
Fig. Hcp Li particles in a matrix of bcc Mg-Li.