Papers by Author: Bernard Bolle

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Authors: Bernard Bolle, Albert Tidu, L. Jolly, Christophe Valot, C. Laruelle, J.J. Heizmann
Authors: Y.D. Liu, X. Zhao, Albert Tidu, Bernard Bolle, Liang Zuo, J.J. Heizmann
Authors: Thierry Grosdidier, Y. Samih, Nathalie Allain-Bonasso, Bernard Bolle, Z.X. Zou, Y. Quin, Sheng Zhi Hao, Chuang Dong
Abstract: The low energy high current pulse electron beam (LEHCPEB) irradiation induces ultra fast dynamic temperature fields in the surface of the material to which is associated dynamic stress fields that causes intense deformation at the material surface and sub-surface. Improved surface properties (hardness, corrosion resistance) can be obtained using the LEHCPEB treatment. Under the “Melting” mode, the top surface (few µm) which is melted and rapidly solidified (107 K/s), can solidify has nano-domains formed from the highly under-cooled melt. The thermal stress wave that propagates in the sub-surface imposes strain hardening and grain size refinement. This induces a sub-surface hardening that can extent over about 100 µm. The use of the “Heating” mode is less conventional. This mode can promote grain size refinement, hardening as well as texture modification without modification of the sample geometry.
Authors: B. Petit, Nathalie Gey, Michel Humbert, Bernard Bolle, M. Cherkaoui
Abstract: A micromechanical model was used to simulate the mechanical behaviour, the transformation kinetic and the texture evolutions of a 304 stainless steel, deformed by tensile tests at T=–60°C. When the transformation strain is calculated with the phenomenological theory, the model does not very well predict the observed transformation rate and the texture evolution of the main γ grain orientations. XRD and EBSD analyses show that the martensitic transformation of γ phase into α’ martensite involves the intermediate ε phase. From these observations, new simulations were performed in which only the γ→ε transformation strain is considered in competition with classical plasticity of austenite. The α’ variants were calculated in a second step, from the ε variants selected in the micromechanical model. Among the 6 potential α’ variants able to nucleate from the same ε variant, the best oriented ones, with respect to the applied stress were selected. Under these conditions, the numerical simulations reproduce the experimental results in a more satisfying way.
Authors: Y. Samih, Bernard Bolle, N. Alain-Bonasso, Sheng Zhi Hao, Chuang Dong, Thierry Grosdidier
Abstract: The present paper presents the first results of an ongoing research dedicated to the analysis of microstructure in steels surfaces treated by Low Energy High Current Pulsed Electron Beam (LEHCPEB). Various steels - 316L (a stainless steel), D2 (a cold-worked die steel) and 4Cr13 (a martensitic steel) - have been treated by LEHCPEB in order to improve the understanding of the surface microstructure modifications induced by this treatment. The microstructures in the modified surface were characterized by microscopy and diffraction techniques.
Authors: Thierry Grosdidier, Bernard Bolle, J.D. Puerta Velásquez, J.X. Zou, Jean-Jacques Fundenberger, Nathalie Allain-Bonasso, P. Chevrier, Albert Tidu
Abstract: This paper reviews some recent results concerning surface integrity of materials processed with two important developing techniques: high speed machining (HSM) – here applied to the difficult case of Ti alloys – and low energy high current pulsed electron beam (LEHCPEB) surface treatment of steels. The effect of the processing parameters on the development of microstructure, texture and residual stresses is detailed for modifications occurring both at the surfaces and sub-surfaces.
Authors: J.D. Puerta Velásquez, L. Lavisse, J.C. Kneip, H. Andrzejewski, P. Chevrier, Bernard Bolle, Albert Tidu, S. Matteï
Abstract: A titanium alloy Ti-6 Al(wt%)-4V(wt%) was treated in air by Nd:YAG laser radiation (wavelength of 1.064 %m) in continuous mode. Targets were irradiated globally with different levels of energy (accumulated fluence) at constant power. Different focal lengths and beam displacement velocities were used. Cross section microstructural observations were carried out by scanning electron microscopy. Backscattered electron imaging reveals microstructural modifications in samples. A structural phase transformation of beta (bcc) to alpha prime (hcp) phase was observed. The depth of the transformed zone observed by phase transformation is dependent on the treatment parameters. Conformity between microstructural observations and the treatment parameters is discussed with reference to thermal simulations.
Authors: Y.D. Liu, Albert Tidu, Bernard Bolle, Liang Zuo, J.J. Heizmann
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