RELATION BETWEEN HARDNESS OF (Ti, Al)N BASED MULTILAYERED COATINGS AND PERIODS OF THEIR STACKING

This study aims to model, by using a finite element method, the relationship between the hardness and the period Λ of metal/nitride multilayer coatings (Ti0.54Al0.46/Ti0.54Al0.46N)n in order to understand the increase of the hardness at the low periods [1] and then optimise the multilayer coating architecture to obtain the best mechanical properties. A 2D axisymmetric finite element model of the Berkovich nanoindentation test was developed. The coating was designed as a stacking of Ti0.54Al0.46 and Ti0.54Al0.46N nanolayers with, in the first hypothesis, equal thickness and perfect interface. The elastoplastic behaviours of the metal and nitride layers were identified by Berkovich nanoindentation experiments and inverse analysis on thick monolayer samples. The indentation curves (P-h) obtained by this model depend on the period Λ of the stacking. Simulated (P-h) curves were compared with experimental data on 2 μm thick films with different periods Λ ranging from 10 to 50 nm deposited by RF magnetron sputtering using reactive gas pulsing process (RGPP). The model forecasts are very consistent with the experience for the largest period but the model does not reproduce the hardness increase at the lowest periods. The Λ = 10 nm coating was analysed by electron energy loss spectroscopy (EELS) on a transmission electron microscope. Results show intermixing of the layers with the presence of nitrogen atoms in the metal layer over a few nanometers [1]. It was concluded that the metal/ceramic interface plays an important role at low periods. The addition in the model of a transition layer in the metal/nitride stacking, with an elastoplastic metal/ceramic medium behaviour, allows to reproduce the nanoindentation experimental curves. The thickness of this transition layer deduced from model updating method is in very good agreement with EELS observations

Indentation de films minces Ti1-xAlxN (0=x=1) : analyse mécanique et structurale

Des films minces Ti1-xAlxN (0 x 1) ont été étudiés par DRX, puis par microindentation associée à de la simulation par éléments finis. Les empreintes d'indentation sont analysées à partir d'images MET sur des lames amincies par FIB. Les résultats montrent des relations entre la structure cristalline, le mode de croissance et l'endommagement des couches en fonction de x. La forte proportion de joints de grains dans les films riches en Ti permet un glissement des zones cristallines sous l'effet des contraintes de cisaillement. Les films riches en Al sont plus texturés et fragiles

Mécanismes d'usure de revêtements de nitrure de titane et d'aluminium en microtribologie

Le comportement à l’usure de films minces de Ti1-xAlxN (0 ≤ x ≤ 1) déposés par PVD est caractérisé et analysé en fonction de la micro et nano-structure des couches. La structure de ces films est à l’origine de leurs propriétés fonctionnelles. Les directions de croissance des films nanostructurés ont été mesurées par diffraction des rayons X. Les modes d’endommagement des films ont été obtenus par des essais de microtribologie à température ambiante contre une bille d’alumine pour pallier l’usure du pion, à faible chargement et faible vitesse de glissement, pour éviter la formation de couches d’oxyde en surface. Pour comprendre les mécanismes d’usure engendrés par le frottement de la bille, plusieurs essais ont été mis en œuvre : détermination de la ténacité par des essais de rayure, observation de la trace par microscopie électronique à balayage et mesure du volume d’usure après plusieurs allers-retours par profilométrie interférométrique par holographie. Lorsque les débris d’usure restent piégés dans le sillon, leur quantité, directement liée à la résistance à l’initiation de fissures du revêtement, et leur nature, ductiles ou fragiles, ont une grande influence sur l’endommagement final. Les films à forte teneur en aluminium texturés selon la direction [002] du réseau hexagonal, présentent un comportement fragile. Lorsque la teneur en aluminium augmente, le nombre de cycles au bout duquel le coefficient de frottement subit un accroissement considérable diminue. Le nombre de cycles à partir duquel le coefficient de frottement augmente considérablement diminue lorsque la concentration en aluminium augmente. Les films riches en titane dont la direction principale de croissance est [200] du réseau cubique, présentent un meilleur comportement à l’usure. Pour ces films ductiles, l’existence de domaines orientés suivant la direction [111] semble jouer un rôle important sur la ténacité. En effet, la quantité de débris générés est liée à une plus ou moins grande proportion de domaines cristallisant dans cette direction

Mode-I interlaminar fracture toughness of flax, glass and hybrid flax-glass fibre woven composites: Failure mechanism evaluation using acoustic emission analysis

International audienceThe mode-I interlaminar fracture toughness of flax, glass and hybrid flax-glass fibre woven composites was studied by using a DCB test. The acoustic emission signals recorded during the tests and scanning electron microscope images were used to analyse the damage mechanism of each composite. The crack initiation for the flax-fibre laminate needs the highest energy (1079 versus 945 for hybrid flax-glass fibre and 923 J/m2 for glass-fibre laminates). The morphology of the flax fibres, short and bonded together in bundles to manufacture the twill fabric, allows the creation of a larger amount of fibre bridging as the origin of this highest energy. Furthermore, hybridisation of glass fibres with flax fibres in an appropriate combination offers an interesting solution when the toughness of glass fibre composites needs to be increased. More interesting is the considerable advantage of the composite structure weight reduction due to the low flax fibre density

Structural investigation of thin films of Ti1-x AlxN ternary nitrides using Ti K-edges X-ray Absorption Fine Structure

International audienc

Understanding indentation, scratch and wear behavior of UV-cured wood finishing products

In the wood furniture and flooring industry, the protection and aesthetic properties of the final product often rely, at least partially, on the coatings applied on the wood surface. For flat surfaces, UV-cured coatings are often preferred due to their multiple advantages, such as high curing speeds, low volatile organic compounds (VOC) content, low energy consumption and high crosslinking densities. To increase the durability of interior wood products, the behavior of the protective coatings, while subjected to wear and deterioration, has to be understand in order to be enhanced. According to the type of solicitation, mar (i.e. shallow defect), scratches or indentations can be formed, which impact the coating’s appearance and can shatter the perception of the whole product. In this work, formulations based on different monomer-oligomer couples were prepared and photo-polymerized to investigate their performances. First, the glass transition temperature and the crosslinking density were determined to understand the contribution of both components in the polymeric network formed upon UV-curing. Then abrasion resistance, hardness, scratch and wear resistance were studied. The results showcased the importance of monomer and oligomer structure, functionality and main physical properties. In scratch experiments, hard and brittle coatings tend to display failures at lower loads than soft and ductile ones, whereas hard coatings are able to better withstand higher forces during indentations experiment. Friction experiments also caused subsurface tearing and fissuring in the soft coatings while generating several fractures in harder ones. Furthermore, the best overall mechanical resistance was obtained for the couples achieving high crosslinking density and a correlation between the crosslinking density of UV-cured coatings and their hardness was found. Interestingly, the investigation of tracks after scratch and wear experiments revealed a significant amount of information toward coatings behavior under various mechanical loads

Characteristics of HIV-2 and HIV-1/HIV-2 Dually Seropositive Adults in West Africa Presenting for Care and Antiretroviral Therapy: The IeDEA-West Africa HIV-2 Cohort Study.

HIV-2 is endemic in West Africa. There is a lack of evidence-based guidelines on the diagnosis, management and antiretroviral therapy (ART) for HIV-2 or HIV-1/HIV-2 dual infections. Because of these issues, we designed a West African collaborative cohort for HIV-2 infection within the framework of the International epidemiological Databases to Evaluate AIDS (IeDEA).We collected data on all HIV-2 and HIV-1/HIV-2 dually seropositive patients (both ARV-naive and starting ART) and followed-up in clinical centres in the IeDEA-WA network including a total of 13 clinics in five countries: Benin, Burkina-Faso Côte d'Ivoire, Mali, and Senegal, in the West Africa region.Data was merged for 1,754 patients (56% female), including 1,021 HIV-2 infected patients (551 on ART) and 733 dually seropositive for both HIV-1 and HIV 2 (463 on ART). At ART initiation, the median age of HIV-2 patients was 45.3 years, IQR: (38.3-51.7) and 42.4 years, IQR (37.0-47.3) for dually seropositive patients (p = 0.048). Overall, 16.7% of HIV-2 patients on ART had an advanced clinical stage (WHO IV or CDC-C). The median CD4 count at the ART initiation is 166 cells/mm(3), IQR (83-247) among HIV-2 infected patients and 146 cells/mm(3), IQR (55-249) among dually seropositive patients. Overall, in ART-treated patients, the CD4 count increased 126 cells/mm(3) after 24 months on ART for HIV-2 patients and 169 cells/mm(3) for dually seropositive patients. Of 551 HIV-2 patients on ART, 5.8% died and 10.2% were lost to follow-up during the median time on ART of 2.4 years, IQR (0.7-4.3).This large multi-country study of HIV-2 and HIV-1/HIV-2 dual infection in West Africa suggests that routine clinical care is less than optimal and that management and treatment of HIV-2 could be further informed by ongoing studies and randomized clinical trials in this population

Monogenic Early-Onset Lymphoproliferation and Autoimmunity: The Natural History of STAT3 GOF Syndrome.

Background In 2014, germline signal transducer and activator of transcription (STAT) 3 gain-of-function (GOF) mutations were first described to cause a novel multisystem disease of early-onset lymphoproliferation and autoimmunity. Objective This pivotal cohort study defines the scope, natural history, treatment, and overall survival of a large global cohort of patients with pathogenic STAT3 GOF variants. Methods We identified 191 patients from 33 countries with 72 unique mutations. Inclusion criteria included symptoms of immune dysregulation and a biochemically confirmed germline heterozygous GOF variant in STAT3. Results Overall survival was 88%, median age at onset of symptoms was 2.3 years, and median age at diagnosis was 12 years. Immune dysregulatory features were present in all patients: lymphoproliferation was the most common manifestation (73%); increased frequencies of double-negative (CD4−CD8−) T cells were found in 83% of patients tested. Autoimmune cytopenias were the second most common clinical manifestation (67%), followed by growth delay, enteropathy, skin disease, pulmonary disease, endocrinopathy, arthritis, autoimmune hepatitis, neurologic disease, vasculopathy, renal disease, and malignancy. Infections were reported in 72% of the cohort. A cellular and humoral immunodeficiency was observed in 37% and 51% of patients, respectively. Clinical symptoms dramatically improved in patients treated with JAK inhibitors, while a variety of other immunomodulatory treatment modalities were less efficacious. Thus far, 23 patients have undergone bone marrow transplantation, with a 62% survival rate. Conclusion : STAT3 GOF patients present with a wide array of immune-mediated disease including lymphoproliferation, autoimmune cytopenias, and multisystem autoimmunity. Patient care tends to be siloed, without a clear treatment strategy. Thus, early identification and prompt treatment implementation are lifesaving for STAT3 GOF syndrome. Key word