Thermal stability of nickel structure obtained by high-pressure torsion in liquid nitrogen

Using transmission electron microscopy and durometry, the structural evolution of commercially pure nickel (99.6%) under high-pressure torsion (HPT) in liquid nitrogen and subsequent annealings in the temperature range 100-400A degrees C has been investigated. In this nickel, at cryogenic temperature, HPT gives rise to a nanocrystalline structure with the record high microhardness (6200 MPa) and average crystallite size similar to 80 nm. The obtained structure is stable at room temperature and possesses a relatively low thermal stability, since recrystallization occurs at lower temperatures than after conventional deformation or HPT at room temperature.