Regensburg 2007 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 12: Growth
MM 12.5: Talk
Monday, March 26, 2007, 17:15–17:30, H6
Recrystallisation phenomena of HPT-processed 99.99% iron. — •Kejing Yang1, Ralf Theissmann2, Julia Ivanisenko2, and Hans-Jörg Fecht1,2 — 1Materials Division, University of Ulm, 89091 Ulm, Germany — 2Institut für Nanotechnology, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany
The understanding of mechanisms governing the recrystallisation of nanocrystalline metals and alloys is important for fundamental materials science, but also for practical applications of such materials, because it can help to find out the routs for improvement of their thermal stability. We conducted a comprehensive investigation of microstructure evolution upon annealing in the temperature range between 100°C and 400°C of high purity (99.99%) iron processed by severe plastic deformation using transmission and orientation imaging microscopy, and XRD analysis. The as-processed microstructure was typical of severely deformed metals consisting of grains with a mean size of 160 nm, and subgrains with a mean size of 90 nm. The grain boundaries originated from plastic deformation are in non-equilibrium state, which is manifested in presence of steps and facets in their structure, and a high level of micro stresses of 0.2 %. After annealing at 200°C for 1 hour, a growth of both grains and subgrains was observed, and after 400°C the microstructure was completely recrystallised. The mechanism of recrystallisation of as-processed iron was of continuous type. Surprisingly, a very high dislocation density was observed in grains after recrystallisation. Presumably, these dislocations appeared as a result of migration of grain boundaries with steps.