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

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

Modelling nanoparticles formation in the plasma plume induced by nanosecond pulsed lasers

Nanoparticles formation in a laser-induced plasma plume in the ambient air has been investigated by using numerical simulations and physical models. For high irradiances, or for ultrashort laser pulses, nanoparticles are formed by condensation, as fine powders, in the expanding plasma for very high pairs of temperature and pressure. At lower irradiances, or nanosecond laser pulses, another thermodynamic paths are possible, which cross the liquid-gas transition curve while laser is still heating the target and the induced plasma. In this work, we explore the growth of nanoparticles in the plasma plume induced by nanosecond pulsed lasers as a function of the laser irradiance. Moreover, the influence of the ambient gas has also been investigated

Influence of the composition of titanium oxynitride layers on the fretting behavior of functionalized titanium substrates: PVD films versus surface laser treatments

International audienceAbstract In this work we compared the fretting behavior of pure titanium plates functionalized with titanium oxynitride surface layers, obtained by two methods: a Physical Vapor Deposition (PVD) method, reactive magnetron sputtering, and Surface Laser Treatments (SLT), under different mixtures of oxygen and nitrogen. The composition of the layers was determined by nuclear reaction analysis (NRA) and their structure was analyzed by Raman spectroscopy. PVD layers were TiN-like fcc layers, with an oxygen concentration going from 36 to 50 at.%. Three SLT layers were studied. The first one was a TiN-like layer containing ~28 at.% of oxygen. The second one was formed of different titanium oxide phases containing ~5 at.% of nitrogen. The third one was a titanium dioxide layer with a negligible concentration of nitrogen. It was found that the steady friction coefficient was similar for all the layers and quite lower than that measured for uncoated Ti. The study of the fretting scars revealed a higher resistance of SLT layers to fretting wear, which can be due to the smooth layer-substrate interface. The detachment of coating particles was observed in some PVD layers. Finally, the transfer of matter between the first bodies was studied by micro-Raman spectroscopy and nuclear reaction techniques: NRA and Particle Induced X-ray Emission