Papers by Author: Colin Scott

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Authors: Eglantine Courtois, Thierry Epicier, Colin Scott
Abstract: Niobium is a strong carbide forming element which is often used in microalloyed steels to control the grain size during thermomechanical treatments and to provide strengthening through precipitation processes. A detailed microscopic investigation is one of the keys for understanding the first stages of the precipitation sequence, thus Transmission Electron Microscopy (TEM) is required. The main difficulty of TEM studies is due to the nanometre scale dimensions of the particles, which makes their detection, structural and chemical characterization delicate. Model Fe- (Nb0.06%,C0.05%) and Fe-(Nb0.05%,C0.03%,N0.03%) ferritic alloys subjected to isothermal annealing treatments have been investigated. High Resolution TEM (HRTEM) and conventional TEM (CTEM) were used to characterise the morphology, nature and location of precipitates. Volume fraction measurements and a statistical approach to the determination of precipitate size histograms have been investigated using Energy Filtered TEM (EFTEM) and High Angle Annular Dark Field (HAADF) imaging. Chemical compositions were quantified by Electron Energy Loss Spectroscopy (EELS). The evolution of precipitate composition with time and temperature is compared with previous simulations obtained from new thermodynamic models based on equilibrium boundary conditions.
Authors: C. Iparraguirre, Ana Isabel Fernández-Calvo, Beatriz López, Colin Scott, A. Rose, W. Kranendonk, B. Soenen, G. Paul
Abstract: In this contribution strain induced precipitation of niobium carbides has been analyzed making use of different hot-rolling simulators and combining the advanced precipitation characterization methods of selective chemical extraction and transmission electron microscopy. A laboratory cast Fe-0.1C-0.07Nb alloy has been employed for the study. Thermomechanical simulations were carried out by torsion, plastodilatometry and plane strain compression techniques. The results have shown that, in spite of the different deformation modes a relatively good correlation is obtained between the measurements of the precipitate size and the amount of Nb precipitated in the different experiments.
Authors: J.L. Collet, Françoise Bley, Alexis Deschamps, Colin Scott
Abstract: The deformation mechanisms of an Fe-Mn-C TWIP steel have been investigated as a function of deformation and deformation temperature, using synchrotron X-ray diffraction at the European synchrotron radiation facility. Using the Warren theory, it is possible to reach a good qualitative understanding of the deformation mechanisms. We have confirmed that the deformation mechanisms shifted from the formation of martensite at very low temperature, to twinning around room temperature and dislocations at higher temperatures. Although some quantification of the density of crystalline defects can be reached using simple parameters such as peak shift and broadening, the complexity of defects present in this material require the development of more advanced data interpretation models. First results are shown, using shift and broadening of the peak and fit of intensity by a pseudo-voigt function, as well as the study of the asymptotic behavior of the intensity.
Authors: J.L. Collet, Françoise Bley, Alexis Deschamps, H. de Monestrol, Jean François Berar, Colin Scott
Abstract: Fully austenitic steels of the Fe-Mn-C system can show extensive deformation twinning (TWIP effect). The deformed microstructure of such steels has been analysed using X-ray diffraction at the European Synchrotron Radiation Facility (ESRF). The experimental diffractograms, recorded using a 2D CCD camera, are analysed in terms of Bragg peak profiles (broadening and asymmetry) and position (shift from the reference [undeformed state] position) leading to an estimation of dislocation and stacking faults densities.
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