Effect of laser shock peening on the high temperature oxidation resistance of titanium

The effect of laser shock peening on the high temperature oxidation resistance of commercial pure titanium at high temperature (700 °C) was studied in long-time (3000 h) exposure under dry air. A reduction of the gain mass by a factor 4 was found for laser-shock peened (LSP) samples compared to untreated titanium, which supports the interest of laser-shock treatment for the improvement of high temperature resistance. Short-durations (10 h and 100 h) oxidation experiments, devoted to investigate the influence of the LSP treatment on the first stages of the oxidation process, were also carried out by TGA. Several techniques as scanning electron microscopy, hardness and roughness measurements, X-ray diffraction and X-ray photoelectron spectrometry, micro-Raman spectroscopy, nuclear reaction analysis and electron backscattered diffraction were used to characterize the sample after laser treatment and oxidations. The formation of a continuous nitrogen-rich layer between the oxide layer and the α-case area in LSP samples appears to be the key factor to explain the reduction of oxygen diffusion, and thus the improvement of the oxidation resistance of laser shocked titanium. Moreover, the grain-texture of LSP samples after oxidation can also explain the improvement of the high temperature oxidation resistance after long times exposures

Decreased hippocampal translocator protein (18 kDa) expression in alcohol dependence: a [11C]PBR28 PET study

Repeated withdrawal from alcohol is clinically associated with progressive cognitive impairment. Microglial activation occurring during pre-clinical models of alcohol withdrawal is associated with learning deficits. We investigated whether there was microglial activation in recently detoxified alcohol-dependent patients (ADP), using [11C]PBR28 positron emission tomography (PET), selective for the 18kDa translocator protein (TSPO) highly expressed in activated microglia and astrocytes. We investigated the relationship between microglial activation and cognitive performance. Twenty healthy control (HC) subjects (45±13; M:F 14:6) and nine ADP (45±6, M:F 9:0) were evaluated. Dynamic PET data were acquired for 90 min following an injection of 331±15 MBq [11C]PBR28. Regional volumes of distribution (VT) for regions of interest (ROIs) identified a priori were estimated using a two-tissue compartmental model with metabolite-corrected arterial plasma input function. ADP had an ~20% lower [11C]PBR28 VT, in the hippocampus (F(1,24) 5.694; P=0.025), but no difference in VT in other ROIs. Hippocampal [11C]PBR28 VT was positively correlated with verbal memory performance in a combined group of HC and ADP (r=0.720, P<0.001), an effect seen in HC alone (r=0.738; P=0.001) but not in ADP. We did not find evidence for increased microglial activation in ADP, as seen pre-clinically. Instead, our findings suggest lower glial density or an altered activation state with lower TSPO expression. The correlation between verbal memory and [11C]PBR28 VT, raises the possibility that abnormalities of glial function may contribute to cognitive impairment in ADP

Microstructural and tribological study of Nd:YAG laser treated titanium plates.

International audienceIn this work, the fretting behaviour of pure Ti plates laser treated with a Nd:YAG pulsed laser was compared to that of untreated Ti plates. Fretting tests were done at room temperature without lubrication. The contact geometry was a cylinder (bearing steel) on a plane. The evolution of both the ratio, m ¼ Q=P, between the normal and the tangential forces, and the Fouvry's energy criterion ðAÞ were recorded as a function of the number of fretting cycles, N. Energy dispersive spectrometry and micro- Raman spectroscopy were used to analyse the fretting scars. The oxidized layer formed by the laser treatment displayed a mixed slip regime as a function of N, and a smaller fretting coefficient m than the titanium reference

Incorporation d'azote et d'oxygène dans les nanoparticules formées par traitement de surface laser de cibles métalliques dans l'air

International audienceLors de l'irradiation de matériaux métalliques tels que l'aluminium, le fer ou le titane par un faisceau laser de courte durée d'impulsion (de l'ordre de la nanoseconde), il se forme une vapeur très énergétique et fortement ionisée appelée plume-plasma. A la fin de l'interaction, ce plasma se refroidit et se détend à des vitesses supersoniques. Des nanoparticules résultent de la condensation de cette vapeur métallique dans l'air, donc de la réactivité chimique avec les gaz réactifs de l'air tels que l'azote et l'oxygène. L'objectif de cette étude est de quantifier la quantité d'éléments légers afin de comprendre les mécanismes physiques mis en jeu dans le plasma, créé lors de l'interaction laser-cible, qui conduisent à la formation de nanoparticules essentiellement sous la forme d'oxyde voire de nitrure dans le cas de l'aluminium. Dans le but d'analyser les particules au plus près de leur milieu de formation, une analyse « in-situ» par diffusion des rayons X aux petits angles (S.A.X.S.) sous atmosphère contrôlée avait permis d'étudier l'influence de l'oxygène sur la taille et la morphologie des particules formées . Par ailleurs, des caractérisations « ex-situ» ont été également réalisées sur des particules déposées sur des plaques de verre exposées au voisinage de la plume, par spectroscopie micro-Raman, par diffraction aux rayons X (DRX) et par microscopie électronique à transmission (MET). Toutefois, la plupart de ces techniques de caractérisation nécessitent la présence de formes cristallines et en quantité suffisante. Par l'usage des réactions nucléaires induites par les deutérons sur l'oxygène-16 et l'azote-14, la microanalyse nucléaire permet de mesurer les quantités totales d'oxygène et d'azote insérées en fonction des conditions opératoires (nature de la cible, composition des mélanges de gaz de l'atmosphère environnante). On présentera l'état de l'art de la connaissance de ces poudres et on montrera quelques exemples de cartographies quantitatives réalisées sur des amas de nanoparticules

High Temperature Oxidation Kinetics of Shot-Peened and Laser-Shock Peened Ti-Beta-21S

Isothermal oxidation tests of mechanically treated Ti-Beta-21S (TIMET, Ti-15Mo-3Nb-3Al-2Si, ASTM Grade 21) were performed under dry air at 650, 700 and 750 °C for 100 h and compared to untreated samples. Two different mechanical surface treatments were used: ultrasonic shot-peening (SP) and laser-shock peening (LSP). The study investigates the effect of both treatments on the oxidation kinetics of the process and the role of atmospheric nitrogen insertion. With this aim, oxidation experiments were also performed under pure oxygen. The results show that the oxidation is governed by diffusion after a short transient time. Both SP and LSP treatments improve the high temperature oxidation resistance of Ti-Beta-21S in dry air, but not in pure oxygen. The formation of a nitrogen-enriched layer at the oxidemetal interface, which is promoted by the mechanical surface treatments, explains the increase in the oxidation resistance in air by slowing down the diffusion of oxygen into the metal

German theory and practice of war,

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Growth of titanium oxynitride layers by short pulsed Nd:YAG laser treatment of Ti plates: Influence of the cumulated laser fluence.

International audienceTitanium oxynitride layerswere formed by surface laser treatment of Ti plates in air using a Nd:YAG laser source of short pulse duration about 5 ns. The cumulated laser fluence was varied in the 100–1200 J cm2 range and its influence on the composition and the structure of the formed layers was studied by different characterization techniques providing physico-chemical and structural information. It was shown that the laser treatment induces the insertion of light elements as O, N and C in the formed layer with the amount increasing with the laser fluence. The in-depth composition of the layers and the co-existence of different phases were also studied. The way in which the laser parameters such as fluence affect the insertion of nitrogen and oxygen was discussed in connection with the effects of the plasma plume formed above the target