THERMAL BEHAVIOR OF PURE NI DEFORMED BY HIGH PRESSURE TORSION TO ULTRA-HIGH STRAIN

摘要

Polycrystalline Ni (99.967%) has been deformed to an ultra-high strain of ε_(vM)=100 by high pressure torsion at room temperature. The samples at this strain are nanostructured with an average boundary spacing of 130 nm and a fraction of high angle boundaries (>15°) of 74%. The deformed samples have been annealed isochronally for 1h at temperatures from 100-600°C, and the evolution of the structural parameters (boundary spacing, average boundary misorientation angle and the fraction of high angle boundaries), crystallographic texture and hardness has been determined. It has been observed that high strain leads to rapid recovery and recrystallization, as an example, the recrystallization temperature has decreased to 160°C. The recrystallization grains are less than 2-3 μm and the fraction of high angle boundaries is about 90%. An analysis shows that the highly strained sample recrystallizes discontinuously i.e. by nucleation and growth, leading to different recrystallization textures.