Papers by Author: Francis Wagner

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Authors: Anthony D. Rollett, Francis Wagner, Nathalie Allain-Bonasso, David P. Field, Ricardo A. Lebensohn
Abstract: We examine the relationship between local gradients in orientation, which are quantified with the Kernel Average Misorientation, and the grain boundary network in an interstitial-free steel sheet, before and after 12% tensile strain. A portion of the unstrained microstructure is used as input to a full-field spectral viscoplastic code that simulates the same deformation. The orientation gradients are concentrated near grain boundaries in both experiments and simulation. Mapping out stress gradients in the simulation suggests that the development of orientation gradients is strongly correlated with such gradients.
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: P. Rendtel, Francis Wagner, Rolf Janßen, N. Claussen
Authors: Nathalie Bozzolo, Grzegorz Sawina, Francois Gerspach, Krzystof Sztwiertnia, Anthony D. Rollett, Francis Wagner
Abstract: Grain boundary character in samples of Zr701 annealed at two different temperatures has been investigated in terms of lattice misorientation. The main difference between the two samples was the extent of grain growth post-recrystallization. The textures were typical for the material. Differences between the texture-based misorientation distribution function (T-MDF) and the microstructure-based MDF (M-MDF) revealed significant preferences for certain grain boundary types, notably those with <11-20> rotation axes.
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: Abdelhak Ayad, Nathalie Allain-Bonasso, Nadjet Rouag, Francis Wagner
Abstract: From an EBSD map made on a polycrystal one can define a set of grains using a criterion of misorientation between the adjacent pixels. Once such a list of grains is obtained, various quantities can be associated to each grain such as its size, (mean) orientation, GOS (Grain Orientation Spread) etc... The GOS associated to one grain is the mean value of the misorientations between all the pixels of the grain and the mean orientation of the grain. This value is quite sensitive to the state of the material (degree of plastic deformation, degree of recrystallization for example). Therefore it can help in interpreting the evolution of a microstructure during thermomechanical treatments. It is the purpose of this presentation to provide GOS values for an IF steel after several degrees of plastic deformation as well as after several annealing treatments which lead to partially or totally recrystallized states. The sources of influence on GOS values (as grain detection limit or grain size) are analyzed. The link between the values and the state of the material will be discussed at a global stage for a given population of grains.
Authors: Claude Esling, Michel Humbert, M.J. Philippe, Francis Wagner
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: P. Keramidas, R. Haag, Thierry Grosdidier, P. Tsakiropoulos, Francis Wagner
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