Guillaume Geandier

Bio: Guillaume Geandier is an academic researcher from University of Lorraine. The author has contributed to research in topics: Austenite & Martensite. The author has an hindex of 23, co-authored 118 publications receiving 1330 citations. Previous affiliations of Guillaume Geandier include European Synchrotron Radiation Facility & Lawrence Berkeley National Laboratory.

Metallurgical study on chips obtained by high speed machining of a Ti–6 wt.%Al–4 wt.%V alloy

Abstract: A metallurgical analysis on chips obtained by high speed machining of a Ti–6wt.%Al–4wt.%V alloy has been performed to provide a better understanding of chip formation mechanisms. For this purpose, X-ray diffraction, energy dispersive X-ray analysis, scanning electron microscopy and electron backscattering technique were employed. The titanium β phase was observed in all chips for any tested cutting speeds. No evidence of phase transformation was found in the shear bands. Microscopical observations are in agreement with the catastrophic thermoplastic shear model for saw-tooth chip formation, instead of the periodic crack initiation one.

Microstructure and phase composition of microarc oxidation surface layers formed on aluminium and its alloys 2214-T6 and 7050-T74

Abstract: The influence of substrate on the microstructure and phase composition of surface layers synthesised by microarc oxidation (MAO) on aluminium and its alloys 2214-T6 and 7050-T74 is studied using scanning (SEM) and transmission electron microscopy (TEM) as well as cross-sectional X-ray diffraction. MAO layers are composed of three layers and are mainly made of gamma-Al2O3 and alpha-Al2O3 phases. The proportion of each phase depends on the substrate. The external porous layer is mainly composed of the gamma-Al2O3 phase. The internal dense layer can present two aspects according to the percentage of the alpha-Al2O3 phase. The so-called granular aspect indicates a high proportion of “dendrite” defect which results from discharge formation and implies a high percentage of the alpha-Al2O3 phase. The so-called columnar aspect indicates a high proportion of “small channels” associated with a very weak percentage in the alpha-Al2O3 phase. In the latter, it is believed that a Zn alloying element can inhibit the growth of alpha-Al2O3. During the MAO process, discharges likely occur in the vicinity of the MAO layer/substrate interface, probably in the spherical porosities that result from oxygen generated in the thin layer localised at the interface.

In situ characterizations of phase transformations kinetics in the Ti17 titanium alloy by electrical resistivity and high temperature synchrotron X-ray diffraction

Abstract: The β ( BCC ) → α ( HCP ) + β ( BCC ) phase transformation kinetics of the β -metastable titanium alloy Ti17 was studied by in situ high energy X-ray diffraction (XRD) and electrical resistivity. The use of synchrotron radiation ( E = 89.12 keV, λ = 0.01402 nm) allowed to characterize specimens 6 mm in diameter, limiting thus oxidation effects. The α + β → β phase transformation kinetics was characterized during continuous heating up to the β temperature range. The β → α + β transformation was studied in isothermal conditions (dwell at 708 ° C or 750 ° C) and during continuous cooling (cooling rates of 0.05 ° C/s, 0.1 ° C/s and 0.61 ° C/s). The evolutions of the phase fractions are analyzed and compared to kinetics measured by electrical resistivity, showing a good correlation between both methods. In addition, the evolutions of the cell parameters of each phase obtained from XRD patterns are analyzed in regard of the transformation kinetics.

Young modulus and Poisson ratio measurements of TiO2 thin films deposited with Atomic Layer Deposition

Abstract: Atomic Layer Deposition (ALD) allows the deposition of thin films onto flat as well as complex geometry surfaces with excellent conformality. Thicknesses of few atomic layers can be achieved. Moreover, low-temperature deposition is possible and this enables the change of surface properties of many kinds of materials. Good adhesion characteristics and also good mechanical performance of ALD deposited thin films make the technique extremely interesting for several applications, as for example micro-electronics. TiO 2 is a well studied semiconductor material because of its multifunctional properties that open a wide range of applications for example in photocatalysis, optics and solar cells. ALD is extremely completive to other technique, to deposit titania thin films, employed even to improve the biocompatibility of many kind of materials. TiO 2 thin films are deposited with ALD technique at low temperature (90 °C) onto Kapton substrate and then crystallized ex-situ after annealing at 300 °C. X-ray diffraction (XRD) techniques are very suitable for the analysis of structure and microstructure of films and surface layers. In this work, XRD in combination with in situ tensile testing has been applied for the first time to measure elastic properties (elastic modulus and Poisson ratio) of TiO 2 anatase thin films obtained by ALD. For the experimental conditions, the tensile stage was installed in a Synchrotron laboratory of Soleil. The information extracted from diffraction patterns is presented.

Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends

Abstract: Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Quantitative X-ray tomography

Abstract: X-ray computer tomography (CT) is fast becoming an accepted tool within the materials science community for the acquisition of 3D images. Here the authors review the current state of the art as CT transforms from a qualitative diagnostic tool to a quantitative one. Our review considers first the image acquisition process, including the use of iterative reconstruction strategies suited to specific segmentation tasks and emerging methods that provide more insight (e.g. fast and high resolution imaging, crystallite (grain) imaging) than conventional attenuation based tomography. Methods and shortcomings of CT are examined for the quantification of 3D volumetric data to extract key topological parameters such as phase fractions, phase contiguity, and damage levels as well as density variations. As a non-destructive technique, CT is an ideal means of following structural development over time via time lapse sequences of 3D images (sometimes called 3D movies or 4D imaging). This includes information nee...

Recent advances in X-ray microtomography applied to materials

Abstract: This review highlights recent advances in X-ray microcomputed tomography (microCT) as applied to materials, specifically advances made since the first materials microCT review appeared in Internati...