Papers by Author: Oliver Geoffroy

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Authors: Nicolas Meyer, Yves Bréchet, Muriel Véron, Marc Mantel, Pierre Emmanuel Dubois, Oliver Geoffroy
Abstract: Softening kinetics of two 17% chromium (Cr) stainless steel grades that differ in niobium (Nb) content are compared. In the experiments, we observed that a low Nb stabilization makes recrystallization nucleation much faster and prevents incomplete recrystallization. A qualitative interpretation, based on interaction with precipitates, is proposed and explains the main features of the softening kinetics as well as the microstructures obtained. For the Nb stabilized grade, magnetic losses were measured in the deformed state and after recrystallization. Above a specific magnetizing frequency, the deformed state led to smaller losses than the recrystallized state. These results are believed to be attributed to a grain size effect.
Authors: Bogdan Viorel Neamţu, Olivier Isnard, Ionel Chicinaş, Florin Popa, Oliver Geoffroy, Viorel Pop
Abstract: The nanocrystalline Ni3Fe powders were obtained via wet mechanical alloying route in argon atmosphere. As process control agent (PCA) the benzene (C6H6) was used. In order to release the internal stresses an annealing at 350 °C for 4 hours was performed. Alternatively, the nanocrystalline Ni3Fe powder was subjected to a process of incipient recrystallization at 600 °C for 30 minutes in vacuum. The recrystallised powders have a crystallite size of 30 nm. The magnetic properties (the frequencies dependence of permeability and magnetic losses) were investigated in AC field of 0.05, 0.1 and 0.2 T. It was found that the polymerization process has a strong influence over the magnetic properties of compacts. If the polymerization was performed by heating the powders into a mould, generally we observed a positive influence over the permeability but a negative influence over the magnetic losses.
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