Papers by Author: N. Dewobroto

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Authors: N. Dewobroto, Nathalie Bozzolo, Pierre Barbéris, Francis Wagner
Abstract: The microstructure and crystallographic texture in zirconium (Zr702) sheets, initially deformed by 80% cold rolling, are investigated at different stages of the primary recrystallization. Inhomogeneities were observed in the deformed microstructure at different scales down to the submicrometer range. The influence of these inhomogeneities on the local recrystallization mechanisms is discussed. The measurement of the orientation of the new grains shows that the nucleation is definitely not oriented. Since the global texture change is very slight, recrystallization by subgrain growth is probably one of the most important mechanism during the recrystallization process in zirconium.
Authors: Nathalie Bozzolo, N. Dewobroto, Thierry Grosdidier, Pierre Barbéris, Francis Wagner
Abstract: Primary recrystallization of a 80% cold–rolled T40 or Zr702 sheets leads to equiaxed microstructures. Subsequently, only normal grain growth takes place in T40 while a few grains can grow abnormally after sufficient time at high annealing temperature (close to the transus) in Zr702. The grain sizes reached after extended grain growth at moderate temperatures in Zr702 are smaller than in T40. The presence of precipitates in Zr702 is probably responsible for this and also for the abnormal phenomena observed at high temperature in this material. The texture changes occurring in both materials under normal grain growth conditions (often roughly described as “30° rotation around c axes”) are due to the development of the largest grains produced by the primary recrystallization. These large grains are preferentially oriented around {j1=0°, F=30°, j2=30°} for T40 and around {j1=0°, F=25°, j2=30°} for Zr702, orientations which become predominant after extended grain growth.
Authors: N. Dewobroto, Nathalie Bozzolo, Francis Wagner
Abstract: The mechanisms governing the very first stage of static recrystallization in two hexagonal alloys (commercially pure titanium and low alloyed zirconium) are investigated in this paper. Initially fully recrystallized and equiaxed materials were cold-rolled to 80% thickness reduction and subsequently recrystallized at 500°C for short times. High resolution EBSD maps were acquired in a FEG-SEM before and after annealing in order to see where and how the new grains appear. Nonoriented nucleation mechanisms are involved in both materials, and there is a strong correlation between the local deformation substructures and the recrystallization kinetics. Recrystallization is extremely fast in the areas where the deformation cells are small and highly misoriented, i.e. in the areas which underwent severe grain fragmentation. Twinning plays an important role for that purpose in the studied titanium sheet.
Authors: Nathalie Bozzolo, Francis Wagner, N. Dewobroto, Thierry Grosdidier
Authors: Francis Wagner, Nathalie Bozzolo, N. Dewobroto, Nathalie Gey
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