Search results for "Microstructure"
showing 10 items of 707 documents
Microstructure of Fe–ZrSiO4 solid solutions prepared from gels
2012
Abstract Microstructural changes associated with chemical and structural evolution from gels to Fe x –ZrSiO 4 solid solutions are reported. Mineralizer-free Fe x –ZrSiO 4 gels in the compositional range 0 ≤ x ≤ 0.15 were prepared by sol–gel liquid-phase route from mixtures of alkoxides of silicon and zirconium, and iron (III) acetylacetonate, and annealed at different temperatures and/or times. The first step on the whole process to the final Fe x –ZrSiO 4 solid solutions was the formation of aggregated of tetragonal Fe-doped ZrO 2 nanocrystals with diameters smaller than 50 nm. At this stage the tetragonal Fe–ZrO 2 were embedded in amorphous silica resulting nanocomposite materials. The …
Microstructural Evolution from Praseodymium-Containing Zircon Gels to Prx-ZrSiO4 Solid Solutions
2012
Structural evolution and coupled microstructural transformations occurred on annealing mineralizer-free Pr-containing ZrSiO4 gels up to final praseodymium-doped zircon yellow pigments are reported. Gels with nominal compositions Prx-ZrSiO4, 0 ≤ x ≤ 0.125, were prepared from mixtures of zirconium and silicon alkoxides and praseodymium acetylacetonate. Crystallization pathway and microstructural changes of thermally treated dried gels were followed by infrared spectroscopy, X-ray diffraction, field emission scanning and transmission electron microscopies, respectively. Results indicated that the crystallization pathway through the whole process of final Prx-ZrSiO4 solid solutions formation di…
Orthogonal cutting simulation of OFHC copper using a new constitutive model considering the state of stress and the microstructure effects
2016
International audience; This work aims to develop an orthogonal cutting model for surface integrity prediction, which incorporates a new constitutive model of Oxygen Free High Conductivity (OFHC) copper. It accounts for the effects of the state of stress on the flow stress evolution up to fracture. Moreover, since surface integrity parameters are sensitive to the microstructure of the work material, this constitutive model highlights also the recrystallization effects on the flow stress. Orthogonal cutting model is validated using experimental designed cutting tests. More accurate predictions were obtained using this new constitutive model comparing to the classical Johnson-Cook model.
Microstructure impact on high temperature corrosion behavior of AISI 316L stainless steel additively manufactured by Selective Laser Melting (AM-SLM)
2019
International audience; Additive Manufacturing by Selective Laser Melting (AM-SLM) is a near-net shape method producing dense and geometrically complex materials from micrometric powders. This process involves complete melting and very high cooling rates who induce a refinement of microstructure, improving the mechanical properties of the material [1,2]. However, the impact of these new microstructures on real functioning properties, like for instance the high temperature durability, needs to be studied. In this purpose, AISI 316L is considered in this work. Samples elaborated by AM-SLM and by conventional metallurgy were oxidized under laboratory air at 900°C for periods up to 3000h. The r…
Additive manufacturing, new elaboration technique of metallic materials : impact of the microstructure on high temperature durability of AISI 316L st…
2021
Additive Manufacturing (AM) processes are able to elaborate, in a single step, metallic parts with very complex geometry, as close as possible to their final dimensions, based on 3D CAD model. Despite a very large number of studies on AM parameters, very few studies report on the high temperature behavior of the metallic materials produced by these processes. This thesis work evaluates the impact of the Selective Laser Melting (SLM) process on the high temperature durability of the austenitic stainless steel AISI 316L, commercial grade widely used in the industry. For this purpose, the reactivity of SLM samples was studied in different conditions (atmosphere, temperature, isothermal or cycl…
Physical, chemical and mechanical evolution of the fuel-cladding interface in irradiated PWR fuel rods
2022
During the fuel irradiation in nuclear reactor, the fuel-cladding assembly is exposed to several irradiation-induced modifications. The fuel swelling coupled with cladding creep leads to a contact between the fuel and the cladding. The oxygen transport from the UO2 fuel to the zirconium layer induces progressively the Zr-cladding oxidation. This oxidation is initially local with the formation of islets. Then, with the increasing burnup of the fuel, it conducts to a continuous layer of about 8-µm thickness, localized at the fuel-cladding interface. At high burnup, zirconia growths anchor themselves in the periphery of the fuel (which is restructured) leading to pellet/cladding interlocking. …
Mid-infrared strong spectral broadening in microstructured tapered chalcogenide AsSe fiber
2012
We report on the generation of a supercontinuum in a chalcogenide microstructured tapered fiber. The suspended core diameter of the fiber is reduced from 5.5 μm to 0.8 μm in the waist of the tapered region. The zero dispersion wavelength is below 2 μm in the tapered region. To pump the fiber, we use a modelocked laser of 4 ps, with a central wavelength of 1960 nm. With only 150 W peak power in the fiber a supercontinuum is generated from 1300 to 2600 nm taking the supercontinuum wavelength edge at -30 dB from the continuum.
Nonlinear femtosecond pulse propagation in all-solid photonic bandgap fiber
2009
Nonlinear femtosecond pulse propagation in all-solid photonic bandgap fiber is investigated experimentally and numerically for both the photonic bandgap guiding in the central silica core and the total internal reflection in germanium doped inclusions.
Interface engineering for improved light transmittance through photonic crystal flat lenses
2010
In this paper, we present photonic crystal flat lenses with interfaces engineered to improve the light transmittance thanks to a broad angles impedance matching. The interface engineering consists in the realization of antireflection gratings on the edges of the lenses which are designed to reduce the propagative waves reflectivity over a wide range of incident angles. The fabricated structures were measured in optical near-field and a four times enhancement of the light transmission efficiency is reported.
Spatio-temporal beam dynamics in multimode nonlinear optical fibers
2017
We overview recent advances in the spatio-temporal nonlinear dynamics of optical pulses propagating in multimode optical fibers. The Kerr effect leads to spatial beam self-cleaning in a graded-index multimode optical fiber, followed by sideband series generation spanning multiple octaves. Effectively single mode supercontinuum spanning from the visible to the mid-infrared was also demonstrated. Enhancement of Kerr beam self-cleaning was observed in active fiber with quasi-step index profile. Moreover, mutual self-cleaning was recently reported for both the fundamental and the second harmonic beams in optically poled multimode fibers with cubic and quadratic nonlinearity.