Effect of Processing Route on Microstructure and Mechanical Properties of a Ti-3Al-2.5V/TiB Composite

A Ti-3Al-2.5V matrix composite reinforced with 8.5 vol.% TiB was produced using a powder metallurgy route. Processing included the mechanical alloying of Ti-3Al-2.5V and TiB2 powders and Hot Isostatic Pressing (HIP) of the resultant composite powders, to produce a dense billet. These billets were subsequently extruded and/or subjected to various Conversion Heat Treatments (CHT), to complete the transformation of the TiB2 particles into TiB needles. The CHT was performed either before or after extrusion. Microstructures and tensile properties of the materials at each stage of the processing routes were investigated and compared to those of a non-reinforced Ti-3Al-2.5V material, manufactured by the same powder metallurgy route. It has been demonstrated that the processing routes have a great impact on the mechanical properties, through modifications of the matrix and reinforcement characteristics. Well-chosen processing routes lead to more ductile composites, though this gain in ductility leads to slightly lower stiffness and strength values. This study clearly demonstrates the possibility to produce, at an industrial scale, a ductile version of a highly reinforced titanium matrix composite, showing important application potential

Muscle activation during gait in children with Duchenne muscular dystrophy

The aim of this prospective study was to investigate changes in muscle activity during gait in children with Duchenne muscular Dystrophy (DMD). Dynamic surface electromyography recordings (EMGs) of 16 children with DMD and pathological gait were compared with those of 15 control children. The activity of the rectus femoris (RF), vastus lateralis (VL), medial hamstrings (HS), tibialis anterior (TA) and gastrocnemius soleus (GAS) muscles was recorded and analysed quantitatively and qualitatively. The overall muscle activity in the children with DMD was significantly different from that of the control group. Percentage activation amplitudes of RF, HS and TA were greater throughout the gait cycle in the children with DMD and the timing of GAS activity differed from the control children. Significantly greater muscle coactivation was found in the children with DMD. There were no significant differences between sides. Since the motor command is normal in DMD, the hyper-activity and co-contractions likely compensate for gait instability and muscle weakness, however may have negative consequences on the muscles and may increase the energy cost of gait. Simple rehabilitative strategies such as targeted physical therapies may improve stability and thus the pattern of muscle activity

Composites à matrice titane et renforts TiB élaborés par métallurgie des poudres : cinétique de transformations des phases, formation des microstructures et propriétés mécaniques

The work done in this PhD thesis aims at the understanding of, on the one hand, the structural and microstructural evolutions of a TiB reinforced titanium matrix composite during the various steps and treatments of the powder metallurgy route used to produce it, and, on the other hand, the link between the microstructures and the mechanical properties for this material. The phase transformation kinetics, in the matrix and in the reinforcement, were characterised using in situ high energy XRD, during these treatments. Microstructural analysis, using SEM, SEM-EBSD and TEM (EDX and EELS) complete the XRD analysis. The matrix phase transformation kinetics were shown to be highly impacted by the processing route (a 300°C shift toward the high temperatures is found for the ß transus temperature). This shift has been linked with an increase in interstitial elements, coming from the powder mechanical alloying and from the interstitials in the TiB2 powder used to produce the TiB. The in situ study also helped in clarifying the transformation sequence of the TiB2 into TiB-27, via the formation of the metastable phase TiB-Bf. SEM and TEM analysis allowed to get access to and discuss the morphological and spatial evolutions of the phases (matrix and borides) during the various treatments and to characterise the chemical composition of the borides. A transformation sequence has been proposed. Finally, in a last part, composite materials were elaborated and submitted to defined heat treatments. The link between the static mechanical properties and the morphological and texture evolutions in the matrix and in the borides, was discussed. Some treatments were proposed to reach optimum mechanical propertiesLes travaux réalisés dans cette thèse visent d’une part, à comprendre les évolutions structurales et microstructurales d’un composite à matrice titane et à renforts TiB au cours des différentes étapes d’élaboration par métallurgie des poudres et des traitements thermiques associés, et d’autre part, à établir des relations entre microstructures et propriétés mécaniques pour ce matériau. Les cinétiques de transformations des phases de la matrice et du renfort ont été caractérisées par DRX haute énergie in situ, au cours des différents traitements du cycle de fabrication. Des analyses de la microstructure par MEB, MEB EBSD et MET (EDX et EELS) complètent l’analyse par DRX. Il a été montré que les cinétiques de transformation de la matrice des composites sont fortement affectées (décalage d’environ 300°C vers les hautes températures de la température de transus ß) par le procédé de fabrication. Ce décalage a été associé à un enrichissement en éléments interstitiels dû au broyage mécanique des poudres et aux interstitiels présents dans les renforts TiB2 introduits pour former le TiB. L’étude in situ a aussi précisé la séquence de transformation du diborure de titane en borure TiB–B27 via la formation de la phase métastable TiB-Bf. Les analyses par MEB et MET ont permis d’atteindre et de discuter des évolutions morphologiques et spatiales des phases (matrice et borures) au cours des différents traitements, et de caractériser la composition chimique des borures. Une séquence de transformation du renfort est proposée. Enfin, des matériaux composites ont été élaborés et soumis à divers traitements thermomécaniques. Le lien entre les propriétés mécaniques statiques et les évolutions morphologiques des borures et de la matrice, comme de la texture des phases, a été abordé. Des traitements ont été proposés pour atteindre des propriétés optimale

Titanium matrix composites reinforced with TiB and produced by powder metallurgy : phase transformations kinetics, microstructure formation and mechanical properties

Les travaux réalisés dans cette thèse visent d’une part, à comprendre les évolutions structurales et microstructurales d’un composite à matrice titane et à renforts TiB au cours des différentes étapes d’élaboration par métallurgie des poudres et des traitements thermiques associés, et d’autre part, à établir des relations entre microstructures et propriétés mécaniques pour ce matériau. Les cinétiques de transformations des phases de la matrice et du renfort ont été caractérisées par DRX haute énergie in situ, au cours des différents traitements du cycle de fabrication. Des analyses de la microstructure par MEB, MEB EBSD et MET (EDX et EELS) complètent l’analyse par DRX. Il a été montré que les cinétiques de transformation de la matrice des composites sont fortement affectées (décalage d’environ 300°C vers les hautes températures de la température de transus ß) par le procédé de fabrication. Ce décalage a été associé à un enrichissement en éléments interstitiels dû au broyage mécanique des poudres et aux interstitiels présents dans les renforts TiB2 introduits pour former le TiB. L’étude in situ a aussi précisé la séquence de transformation du diborure de titane en borure TiB–B27 via la formation de la phase métastable TiB-Bf. Les analyses par MEB et MET ont permis d’atteindre et de discuter des évolutions morphologiques et spatiales des phases (matrice et borures) au cours des différents traitements, et de caractériser la composition chimique des borures. Une séquence de transformation du renfort est proposée. Enfin, des matériaux composites ont été élaborés et soumis à divers traitements thermomécaniques. Le lien entre les propriétés mécaniques statiques et les évolutions morphologiques des borures et de la matrice, comme de la texture des phases, a été abordé. Des traitements ont été proposés pour atteindre des propriétés optimalesThe work done in this PhD thesis aims at the understanding of, on the one hand, the structural and microstructural evolutions of a TiB reinforced titanium matrix composite during the various steps and treatments of the powder metallurgy route used to produce it, and, on the other hand, the link between the microstructures and the mechanical properties for this material. The phase transformation kinetics, in the matrix and in the reinforcement, were characterised using in situ high energy XRD, during these treatments. Microstructural analysis, using SEM, SEM-EBSD and TEM (EDX and EELS) complete the XRD analysis. The matrix phase transformation kinetics were shown to be highly impacted by the processing route (a 300°C shift toward the high temperatures is found for the ß transus temperature). This shift has been linked with an increase in interstitial elements, coming from the powder mechanical alloying and from the interstitials in the TiB2 powder used to produce the TiB. The in situ study also helped in clarifying the transformation sequence of the TiB2 into TiB-27, via the formation of the metastable phase TiB-Bf. SEM and TEM analysis allowed to get access to and discuss the morphological and spatial evolutions of the phases (matrix and borides) during the various treatments and to characterise the chemical composition of the borides. A transformation sequence has been proposed. Finally, in a last part, composite materials were elaborated and submitted to defined heat treatments. The link between the static mechanical properties and the morphological and texture evolutions in the matrix and in the borides, was discussed. Some treatments were proposed to reach optimum mechanical propertie

DEMONSTRATION OF THE APPLICATION OF SUPERPLASTIC FORMING USING INFRARED HEATING EMITTERS TO A PART OF STRUCTURE INCLUDING VARIOUS GEOMETRICAL SINGULARITIES

ArianeGroup and Aurock led a feasibility study through the realization of a scale 1 TA6V demonstrator, using superplastic forming (SPF). ArianeGroup designed the demonstrator according to its knowledge of representative structures, comprising singularities: welds, stiffeners and areas with important thicknesses variations. Aurock performed first numerical simulations of the complete process, putting in evidence the various difficulties to be solved. Then, the demonstrator was physically carried out. Once the demonstration was virtually obtained, each steps of the process were experimented: welding of thick plates with limited deformation, machining of flat panels, pre-forming by rolling and final SPF. For the SPF step, a heating cover and a reinforced refractory castable die were manufactured. Infrared emitters’ position and heating power regulation laws were carefully defined, for the panel to be kept at the correct temperature until being formed. The SPF step led to a successful demonstration of the representative structure. The experimental approach confirmed the process modelling predictability. Limited Scale 1 demonstration was necessary to ensure the process validity with real thicknesses and thickness variations, which are known to mask problems if scale reductions are used without precautions. This methodology can be transfer to a real structure only by tooling adaptations, without additional feasibility works

Structure evolutions in a Ti-6Al-4V matrix composite reinforced with TiB, characterised using high energy X-ray diffraction

International audienceA titanium matrix composite reinforced with TiB was produced using powder metallurgy. A Ti-6Al-4V alloy was chosen to be the matrix, and 12 wt.% of TiB2 was used as the boron source for the solid state formation of TiB. The TiB2 to TiB conversion reaction was studied using an in situ high energy X-ray diffraction technique while heat treating the composite. The TiB2 (space group: P6/mmm) converts into TiB-B27 (Pnma), via TiB-B-f (Cmcm). The metastable character of B-f is confirmed here; it is the first phase formed during the conversion and it progressively converts into B27 during elevated temperature heat treatment. A modification of the phase transformation kinetics in the matrix and of the composite beta transus temperature (T-beta = 1275 degrees C) was also observed, mainly due to gas contamination and intensive work hardening as a result of the mechanical alloying process used to manufacture the material and to a modification of the matrix equilibria

Fictions en esthétique

Inaugurant la collection « Esthétiques hors cadre », ce premier volume représente un pari : réunir, selon une interrogation commune de l'art, des textes suscités par un projet d'écriture et des études à visée théorique. Comment croiser en esthétique l'acte de la fiction et l'analyse de la réflexion ? C'est à faire jouer la multiplicité des rencontres possibles que s'emploie cet essai, auquel ont contribué des écrivains et des chercheurs de notre modernité. Si la fiction appartient à l'art, c'est par les images qui la portent comme par la diction qui s’y dissimule ; mais si la pensée de l'art se fraie une nouvelle voie aujourd'hui, c'est peut-être dans la mesure où elle reconnaît l'exigence fictive qui l'entraîne. Le pluriel de l’art ne tient-il pas à ce qu'il participe simultanément de la recherche d'un principe et de l'abandon à l'événement

Values of selected variables.

<p>Values of selected variables.</p

Correlations between muscle activation, kinematics and functional status in children with DMD.

<p>Correlations between muscle activation, kinematics and functional status in children with DMD.</p

Subject characteristics.

<p>Subject characteristics.</p