Search

Diverse pathways of the deformation-induced transformations are investigated in the β-metastable Ti–12Mo alloy displaying combined TWIP ({332} β twinning) and TRIP (stress-induced α″) effects by means of Schmid factor analysis and in-situ microstructural characterizations. Two sets of Schmid factors, for {332} β twinning and stress-induced martensite, are calculated in grains of random orientation under uniaxial tension condition. Using in-situ EBSD characterization under tension, the correspondence is mapped between primary transformation products and the grain orientations. The correspondence results graphically in four grain-orientation domains in the inversed pole figure triangle, being twin-dominated, martensite-dominated, combination of both, and the domain unfavorable for both transformations. It is also found that the crystallographic partition of the domains, i.e. the selection of transformation pathways with respect to grain orientations, is related to the threshold of Schmid factor for the activation of each transformation and the transformation strain of the corresponding martensite variant. Guided by transformation partition mapping, grains at two special orientations, dominated by stress-induced martensite with-or-without primary {332} β twinning, are targeted in in-situ microstructural observations to clarify the transformation pathways and the underlying deformation mechanisms. Among the different pathways revealed, experimental evidences are highlighted on the unprecedented formation mechanisms of {332} β twins assisted by martensite {130} α″ deformation twinning via two different ways.

International audience; We report results on the processing and characterization of different glass preforms and single core fibers within the SiO2-Na2O-B2O3-Er2O3-P2O5-Al2O3 system. Micro-Raman spectroscopy was used to identify post-draw structural modification. The differences in the micro-Raman spectra recorded on the preform and on the fiber glass were attributed to a change in the structure induced by the drawing process. Changes in the silicate network organization and small scale molecular orientation within the glass matrix are suspected to occur during the fiber drawing process. We found that the extent in the changes between the preform and fiber properties depend on the glass composition. The glass network of the Al-containing fiber is expected to be less sensitive to the drawing process than that of the fiber matrix as the network of this Al-containing fiber is formed by a larger number of Si-BO units in the network and neutral three-coordinated boron compared to the network of the fiber matrix. From the micro-Raman spectra, formation of small crystals is suspected to occur in the P-containing glasses during the fiber drawing process. The resulting fibers were found to have propagation losses at 1330 nm and Er3+ absorption between (7 ± 1) and (25 ± 1) dB/m and (36 ± 1) and (47 ± 1) dB/m, respectively, depending on the glass composition.

International audience; The impacts of electrical parameters throughout PEO development so they can be upgraded to deliver coatings with improved properties were contemplated. Alumina coatings were saved on 6060 aluminum amalgam substrates in a soluble silicate electrolyte utilizing a unipolar pulse DC current mode. The impact of preparing conditions, predominantly electrical parameters (frequency and duty cycle), on the arrangement, development conduct and properties of PEO coatings were researched. Distinctive portrayal techniques including checking electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractometry, and contact tests were utilized to contemplate the microstructure, morphology and properties of the coatings. The connection between the phase of the PEO procedure and the properties of the covering were appeared. The voltage-time reaction was observed to be critical since it gave promptly quantifiable and helpful data about these stages. It was found that the microstructure, morphology, development rate, stage conveyance and organization of coatings could be changed by shifting the electrical parameters.

While ω precipitates in metastable β titanium alloys are typically considered embrittling and consequently deleterious to the mechanical properties, this paper demonstrates that low-temperature aging (LTA) treatments for short time periods can in fact enhance the yield strength while preserving substantial elongation-to-failure in ω containing β titanium alloys. LTA treatments, carried out on a ductile β metastable Ti–12Mo alloy, significantly improve the yield strength of the material (∼55% increase as compared to solution-treated samples) while keeping both TRIP/TWIP effects and a large elongation-to-failure (ε = 0.4 in true strain), resulting in a balance of mechanical properties.

International audience; The chemical durability of glasses with the composition 40P2O5-55ZnO-1Ga2O3-4Ag2O and 41P2O5-51ZnO-8Ga2O3 (mol%) was studied by measuring the rates of aqueous dissolution in neutral, acidic and alkaline aqueous solutions and discussed as a function of the glass composition. The change in the pH of the solutions as a function of the immersion time of the samples was used to study the dissolution mechanism. Using XRD and SEM/EDXA, we showed that the dissolution in deionized (DI) water and HCl consists of the leaching of the phosphate chains into the medium along with (i) the formation of a hydrated layer with the composition Zn2P2O7*3H2O and also of AgCl agglomerates when immersed in HCl and (ii) a leaching out of P, Ga and Ag when immersed for more than 180 min in DI water and for more than 60 min in HCl. The dissolution in NaOH-Na2CO3 consists of a net consumption of the OH− along with the formation of layers of Zn3(PO4)2*(H2O)4 and Zn(H2PO2)2*H2O with no apparent diffusion of P, Ga and Ag when immersed for as long as 240 min. Increasing the Ga2O3 concentration in zinc-phosphate glass at the expense of Ag2O lowers the dissolution rate when immersed in DI water, HCl and NaOH-Na2CO3 probably due to a reinforcement of the glass network.

International audience; Thermal poling was proven successful to induce second order nonlinear properties and concurrent modification of composition, structure and chemical reactivity in glasses. With current efforts to reduce devices sizes in components employing such attributes, means to control changes at the micrometer scale are needed. We present a micro-imprinting poling process to locally tailor surface properties of a glass. Measurements using infrared, Raman and second harmonic generation microscopies confirm that changes in glass structure associated with an induced static electric field are responsible for the enhanced surface reactivity that is successfully controlled at the micrometer scale.

International audience; A new multimodal approach that combines linear and nonlinear vibrational spectroscopies and hyper-Rayleigh scattering has been applied in the TeO2–TaO5/2–ZnO glass system to assess and quantify the relation between Raman gain and optical responses within the glass’ network arrangement. The level of polymerization of the TeO4 chain-like structure in a TeO2 glass system has been identified to be the main parameter for reaching high linear and nonlinear optical constant. We have observed that replacement of TaO5/2 by ZnO strongly modifies the optical properties and, primarily, the Raman and hyper-Raman spectra of the glasses. In particular, we clearly demonstrate a linear relationship between Raman gain and the linear and second-order optical response of the glass, which is directly related to the number density of TeO4 chain-like units. Assuming that only TeO4 chain-like units contribute significantly to the glass’ polarizability, we have found that about 30% of the Te atoms contribute to the hyperpolarizability of the binary system 80TeO2–20ZnO in very good accordance with neutron diffraction results.

Second-order optical susceptibility, χ(2), has been induced in thermally poled chalcogenide glasses, doped with varying levels of sodium. Using alkali-doped chalcogenide glasses, the second harmonic generation (SHG) capability is retained for over a year whereas in alkali-free glasses it disappears in days. The enhanced stability is attributed to a stabilization of the space charge through structural re-arrangements. Polarization-resolved SHG shows that the induced electric field has components in three spatial directions, all with varying extents of stability. Using structured electrodes, we demonstrate the ability to control the various electric field components’ geometry, location and stability to realize a long-lived, nonlinear grating in an alkali-doped chalcogenide glass.

New passive and active oxysulfide glasses have been prepared in the Ge–Ga–Sb–S–O system employing a two-step melting process which involves the processing of the chalcogenide glass (ChG) and its subsequent melting with amorphous GeO 2 or Sb 2 O 3 powder. Optical characterization of the oxysulfide glasses has shown that the UV cut-off wavelength decreases with increasing oxygen content. Using Raman spectroscopy, correlations have been made between the formation of new Ge- and Sb-based oxysulfide structural units, the Sb content and the O/S ratio. We demonstrate the successful processing of active rare earth doped oxysulfide glasses by melting the chalcogenide glass with Er 2 O 3 and Sb 2 O 3 and also by melting the Er 3+ doped chalcogenide glass with Sb 2 O 3 . Modification of the emission spectra at 1500 nm of Er 3+ doped samples with the introduction of oxygen revealed that Er 3+ most likely exists in dual O- and S-neighbor environments. Finally, the photo-response of these new glasses upon near-IR femtosecond laser irradiation has been investigated as a function of Sb content and O/S ratio and shows that the glasses are photo-sensitive to NIR fs laser light with the magnitude of the photo-sensitivity dependent on the glass’ Sb content and O/S ratio.

Silica nanoparticles, prepared by the Stober method, have been doped with Eu 3+ , Dy 3+ , or processed to result in Au nanoparticles on the silica surface. The luminescence of the rare earth (RE)-doped SiO 2 particles has been studied as a function of the nature of the RE, their concentration and also of the presence of Au nanoparticles at the surface of the SiO 2 nanoparticles. We have shown that the Eu 3+ emission is observable over the experimental conditions examined, whereas it was not possible to observe any emission for Dy 3+ doped materials. No enhancement of the Eu 3+ emission was observed following the adsorption of gold nanoparticles at the surface of the SiO 2 nanoparticle, however an excitation at 250 nm leads to both the emission of the matrix and Eu 3+ showing an energy transfer from the SiO 2 matrix to Eu 3+ ions.

International audience; The ability to control glass surface reactivity at different length enables key properties required for future “smart substrates”. Employing a thermal poling process on a specific borosilicate glass composition can yield a surface with tailored physical and chemical properties. This work shows that during poling, alkali contained in the glass matrix migrates from the anode to the cathode side of the specimen, yielding the formation of an alkali-depleted layer under the anode. We have shown that this process is responsible for structural changes in the glass network and the formation of a frozen electric field within the glass. Network reorganization is linked to the creation of BØ3 units, which replace BØ4– entities upon migration of the alkali ions. The resulting newly charged borate structure leads to a measurable change in the glass’ affinity to atmospheric water, being attracted to the poled anodic zone. Such spatial control of surface hydrophilicity can aid in the creation of tailored surface functionality.