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TiAl based alloys are desirable materials for turbine blades in aircraft engines. Depending on alloy composition and temperature additionally disordered β-Ti(Al) (A2 structure) or ordered βo-TiAl (B2 structure) can occur. Unfortunately little is known about the exact order/disorder transformation temperatures of β/βo. We used the good contrast of neutron diffraction for ordering and disordering of TiAl alloys to determine the order/disorder temperatures, which are not accessible by other methods like DSC measurements. Several binary TiAl alloys as well as alloys with additional alloying elements were used to investigate the influence of different Al concentrations and alloying additions on the occurring ordering/disordering reactions and phase transformations. As a result ordered βo phase was found only in selected ternary alloys.

In the present work, the striations and diffraction characteristics of the β phase of Ti-5553 alloy are thoroughly investigated., For the β phase of Ti-5553-type metastable β-Ti alloys, striations in transmission electron microscopy (TEM) bright- and dark-field images have been frequently observed but their origin has not been sufficiently investigated. In the present work, this phenomenon is studied in depth from the macroscopic scale by neutron diffraction to the atomic scale by high-resolution TEM. The results reveal that the β phase contains homogeneously distributed modulated structures, intermediate between that of the β phase (cubic) and that of the α phase or the ω phase (hexagonal), giving rise to the appearance of additional diffraction spots at 1/2, 1/3 and 2/3 β diffraction positions. The intermediate structure between β and α is formed by the atomic displacements on each second {110}β plane in the direction, whereas that between β and ω is formed by atomic displacements on each second and third {112}β plane in the opposite direction. Because of these atomic displacements, the {110}β and {112}β planes become faulted, resulting in the streaking of β diffraction spots and the formation of extinction fringes in TEM bright- and dark-field images, the commonly observed striations. The present work reveals the origin of the striations and the intrinsic correlation with the additional electron reflections of the β phase.

In this paper, three kinds of magnesium matrix composites reinforced by SiCp with the sizes of 0.2, 5 and 10 μm, respectively, were fabricated by stir casting technology. Then the as-cast ingots were deformed by the combination of forging and extrusion process. Typical microstructures were obtained in the composites reinforced by different particle sizes. For the composites with lower volume fraction of particles (2%), submicron SiCp had significant influence on grain refinement and strengthening effect, which resulted in better mechanical properties of submicron SiCp/AZ91 composite. However, mechanical properties reduced owing to the obvious agglomerated submicron SiC particles as the volume fraction increased to 5% and 10%. On the contrary, for micron SiCp/AZ91 composite, the grain size was refined and the strengthening effect was enhanced with the increasing of volume fraction. Although particle size has no influence on the texture type, it has different effects on weakening the intensity of texture.

An unexpected precipitate phase was observed in Mg–20 wt% Dy alloy, with a cuboid morphology not compatible with any shown in the Mg–Dy binary phase diagram. As observed by scanning electron microscopy and energy-dispersive X-ray analysis, the ratio of atomic percent of Dy to Mg is very high in these particles, probably largely because of the poor spatial resolution of that technique but already showing the mismatch with any previously characterized Mg–Dy compound. High-brilliance synchrotron diffraction and transmission electron microscopy experiments confirmed that these particles are composed of DyH2. They are formed during sample preparation at room temperature when hydrogen-containing sources such as water are used.

The effect of trace Mn addition on the microstructure, texture and mechanical properties of the as-cast and as-extruded Mg–5.25 wt.% Zn–0.6 wt.% Ca (ZX51) alloys was investigated in this study. Mn addition had a negligible effect on the grain size of the as-cast ZX51 alloy. However, the addition of Mn led to the obvious decrease of grain size in the as-extruded Mg–5.25 wt.% Zn–0.6 wt.% Ca–0.3 wt.% Mn (ZXM510) alloy, because the Mn addition restricted the grain growth during the hot extrusion process. After the addition of Mn, the basal fiber texture with most of {0 0 0 2} planes parallel to the extrusion direction (ED) was significantly enhanced in the as-extruded ZXM510 alloy. Both tensile yield strength (TYS) and ultimate tensile strength (UTS) were increased in the as-extruded ZXM510 alloy, while the ductility was slightly decreased, which was ascribed to the grain refinement and texture strengthening.

In the present study, 10 vol.% SiCp/AZ91 magnesium matrix composites are fabricated by stir casting. The as-cast ingots are cut into cylindrical billets, and then forged at 420 °C with different deformation amounts (40, 50, 60 and 80%) at a constant RAM speed of 15 mm/s. The results illustrate that the addition of SiC particles has significant influence on refining grain size and improving tensile strength of AZ91 matrix, however, weakening basal plane texture. After forging SiCp/AZ91 composites, the intensity of basal plane texture increases as deformation amount increases. The grain size of composite matrix grows up slightly as the deformation amount increased to 60%, and then it was refined obviously as the deformation amount continues to increase to 80%. The smaller deformation amount is propitious to improve particle distribution, while lager deformation amount promotes SiC particle agglomeration. Thus, the tensile strength increases as the deformation amount increases to 50%, however, it decreases as the deformation amount continues to increase to 80%.

The pure Mg sheets were processed by ARB at 400 °C and 300 °C up to 8 cycles and 4 cycles, respectively. The microstructure was refined during the first cycle and only homogenized during the following ARB process due to the high deformation temperature, intermediate reheating and air-cooling. The ARB process did not show an obvious effect on the tensile properties of the as-ARBed pure Mg sheet due to the stable grain size and dominant basal plane texture during ARB. Further deformation should be introduced to improve the bonding quality of the as-ARBed sheet.

The Mg/Al laminated composite was fabricated by the accumulative roll bonding (ARB) using the pure magnesium and Al5052 alloy at 400 °C. Tensile properties along rolling direction and the transverse direction and the microhardness were evaluated at the ambient temperature. The tensile strength of the laminated Mg/Al composite along both directions increased gradually till two ARB cycles, but then decreased after the third ARB cycles. Optical microscopy and scanning electron microscopy (SEM) were utilized to reveal the microstructure evolution and the failure mechanism. Grain refinement of Mg layers was not obvious during the ARB process due to the high temperature and interval reheating. The obvious crack at the coarse intermetallic compounds and rupture of the Al layer after the third cycle led to the premature failure of the sample along the rolling direction during the tensile test.

SiCp/AZ91 magnesium matrix composite was fabricated by stir casting. The as-cast ingots were cut into cylindrical billets, and then forged at different temperatures (320, 370, 420, 470 and 520 °C) at a constant RAM speed of 15 mm/s with 50% reduction. The microstructure evolution of the composites during forging was investigated by optical microscope, scanning electron microscope, and transmission electron microscope. The texture of the forged composites was measured by neutron diffraction. Mechanical properties of the composite at different forging temperatures were tested by tensile tests at room temperature. It was found that a strong basal plane texture formed during forging, and the intensity of basal plane texture weakened as forging temperatures increased. The particle distribution in the composite was significantly improved by hot forging. Typical microstructures were obtained after forging at different temperatures and the composite with different microstructures offered different mechanical properties during tensile test.

The texture of the Mg/Al laminated composite fabricated by accumulative roll bonding was measured by neutron diffraction. The texture type of the Mg layer was typical rolling texture and the dominant texture of the Al layer was β-fiber rolling texture with scatter around the ideal orientations. The significant waviness structure caused by the shear band reduced both the intensity and the sharpness of the rolling texture of both Mg and Al layers.

Equal channel angular pressing (ECAP) of the in situ Mg2Si reinforced Mg composite was performed with route Bc up to 8 passes using a 90° die. Refinement and re-distribution of the reinforced phase Mg2Si was investigated. Bulk texture development during ECAP was characterized by neutron radiation. Results showed that only the eutectic Mg2Si (Type-II) was proposed to be effective for preparing the in situ Mg2Si/Mg composite. Neutrons texture analysis briefly illustrated that a 〈00.2〉 basal fiber with the obtainment of less shear effect was formed. But the asymmetry of basal fiber around the ECAP direction was also observed. Both uniform texture and homogeneity distribution of Mg2Si particles played an important role in the tensile behavior of ECAPed composite.

Microstructure and texture development of the equal channel angular pressed (ECAP) pure Mg with different rotation routes of A, Bc and C were investigated and related to the tensile mechanical property. Results showed that grain size was greatly decreased after 1 pass but varied with processing routes after the following ECAP. Due to a relatively high processing temperature, the refinement degree was limited via these three routes processing. Different preferred orientations of the basal plane were formed with three routes processing and there existed a rotation angle in (0 0 0 2) pole figure from normal direction to transverse direction. Negative slope of the yield stress versus d−1/2 was obtained with routes Bc processing, which was attributed to the texture modification. Texture strengthening greatly increased the 0.2% yield strength, but decreased the ductility.

© 2015 Elsevier B.V. Room temperature mechanical behavior of extruded Mg-Y-Zn alloys with varying fractions of LPSO phase was studied in tension and compression along the extrusion direction. The microstructure is characterised by elongated LPSO fibers along the extrusion direction within the magnesium matrix. Moreover, the magnesium matrix presents a bimodal grain structure with dynamically-recrystallized grains and deformed, elongated grains with the basal plane parallel to the extrusion direction. The beginning of plasticity depends on the volume fraction of deformed and DRX grains. Alloys with low volume fraction of LPSO phase (, We would like to acknowledge financial support of the Spanish Ministry of Economy and Competitivity and the “Fondo Europeo de Desarrollo Regional” (FEDER) under project number MAT2012-34135. The authors gratefully acknowledge the financial support from the European Union's Seventh Framework Programme for research, technological development and demonstration under the NMI3-II Grant number 283883 to perform the neutron experiments at Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany.

Solid-state refrigeration based on the caloric effects is promising to replace the traditional vapor-compressing refrigeration technology due to environmental protection and high efficiency. However, the narrow working temperature region has hindered the application of these refrigeration technologies. In this paper, we propose a method of combined caloric, through which a broad refrigeration region can be realized in a multiferroic alloy, Ni–Mn–Ga, by combining its elastocaloric and magnetocaloric effects. Moreover, the materials’ efficiency of elastocaloric effect has been greatly improved in our sample. These results illuminate a promising way to use multiferroic alloys for refrigeration with a broad refrigeration temperature region.

Microstructures and tensile properties of commercial pure magnesium processed by rotary swaging (RS) technique were investigated. Bulk and gradient textures in the RS processed Mg were characterised by neutron and synchrotron diffractions, respectively. Grains of the pure Mg were gradually refined with increase in the RS passes, which largely contributed to an increase in the tensile yield strength. A dominated basal fibre texture was observed in the RS processed pure Mg. Accommodated twinning deformation was also observed. Both the optical observations and texture analyses through the diameter of the swaged rod showed a gradient evolution in microstructure.

Mixed rifle has the merit of improving the accuracy, range, and lifetime of gun tube. Due to the large caliber, the deep helix groove, and the long barrel of largecaliber cannon artillery, the traditional way is a complex, reiterative and time consuming process to design an effective cathode for electrochemical machining of rifle. In this paper, in order to improve the efficiency of electrochemical machining and reduce the interference between the rifles and the cathode working teeth, mathematical models are proposed. The computer aided ECM cathode design is described and the three-dimensional cathode body model was set up with UG software. According to the model parameters, the gun tube rifle cathode is designed and manufactured via electrochemical theories, and the experiment was carried out. The experimental results are harmony with the theoretical rifle. It is demonstrated that the computer-aided design for ECM cathode can improve the design precision of cathode, reduce the experimental workload, and shorten the cathode design cycle. Keywords-electrochemical machining (ECM); gun tube; mixed rifle; cathode design; computer aided design

Rotary swaging processing on commercial as-cast pure Mg has been carried out. Bulk texture variation with the processing passes was investigated using large gauge volume by neutron diffraction, of which results showed a combination of different components such as {00.2} basal fibre and two weak {10.0} and {11.0} fibres. Asymmetric distribution of the basal fibre around swaging direction was observed and being related to the processing parameters. Texture gradient analysis by synchrotron radiation demonstrates a non-uniform deformation of the RS processed pure Mg from surface to the centre.

This paper studied for the first time peak intensity, peak position and FHWM pole figures with one time measurement at the neutron diffractometer STRESS-SPEC via in-situ tensile deformation on austenitic steel. Fibre distribution with its evolution from central tensile direction to normal direction of these three kinds of pole figures was obtained. Variation of peak position and FWHM can be correlated to the reorientation of the texture component.

The mode of the maximal undeformed chip thickness was constructed at the condition of small grinding wheel, big cutting depth and creep feed. Comparative experiments of grinding ZrO 2 ceramics with/without ultrasonic vibration were carried out,circular arc grooves were machined on ZrO 2 ceramics block. The experimental results have shown that ultrasonic vibration can descrease grinding force, ZrO 2 Ceramics can be machined with more process remaining by means of creep feed ultrasonic grinding.

The material science diffractometer STRESS-SPEC has high flux and a high flexible monochromator arrangement to optimize the needed wavelength. Many specific sample handling stages and sample environments are available. One of them is a Staubli RX 160 robot with nominal load capacity of 20 kg and more freedom for texture mapping than the Huber 512 Eulerian type cradle. Demonstration experiments of non-destructive pole figures and strain measurements of Cu-tube segments weighing 12 kg weight and 250 mm in length and 140 mm diameter have been carried out. The residual strains measured by the robot and by the XYZ- stage fit quite well, that means the robot is reliable for strain measurements. The texture of the Cu-tube has dominant recrystallization texture components represented by the cube and the rotated cube.

International audience; The influences of uniaxial compressive stress on martensitic transformation were studied on a polycrystalline Ni-Mn-Ga bulk alloy prepared by directional solidification. Based upon the integrated in-situ neutron diffraction measurements, direct experimental evidence was obtained on the variant redistribution of seven-layered modulated (7M) martensite, triggered by external uniaxial compression during martensitic transformation. Large anisotropic lattice strain, induced by the cyclic thermo-mechanical treatment, has led to the microstructure modification by forming martensitic variants with a strong < 0 1 0 >(7M) preferential orientation along the loading axis. As a result, the saturation of magnetization became easier to be reached.

L'auteur a souhaité limiter l'accès aux membres de l'Enseignement supérieur français jusqu'au 31 décembre 2021.; Recrystallization is the intrinsic process of cold-deformed metallic materials that occurs inevitably during the thermal treatment. The produced recrystallization texture contributes to the anisotropy of the mechanical and physical properties. Motivated by the minimization of modern products, 2D materials and laminated composites are increasingly demanded by many applications. Thus, for both scientific and engineering purposes, investigations on the recrystallization of such materials are needed to understand the underlying mechanisms. In this work, Cu foils and graphene nanosheets (GNSs) reinforced Cu matrix laminated composites with Cu foil thicknesses of 10 μm and 30 μm were fabricated, and the recrystallization features were thoroughly investigated from microscale to macroscale by means of SEM-EBSD for microstructure observation, neutron and synchrotron radiation for texture analysis and in-situ synchrotron radiation for lattice strain evaluation. The obtained data were analyzed in the frame of crystallography combined with crystal elasticity and surface energy. The results showed that the recrystallization behavior of the Cu foils were greatly affected by the Cu foil thickness and the addition of the GNSs. For the 10 μm thick Cu foils without GNS, they underwent a transition from the cold-rolling texture to a recrystallization texture dominated by RD-rotated Cube and φ_2-rotated Copper components. The transition was screened by both intrinsic microstructural and extrinsic sample geometrical factors. The orientations of the nuclei were mainly inherited from the deformation orientations. Those with low Taylor factors (Cube, Goss and Brass) demonstrated size preference. The post-nucleation growth was affected by the biaxial thermal elastic constraint and surface energy. Due to their opposite effects, the orientations having moderate biaxial moduli and surface energy density (S, Copper, Brass and recrystallization components) survived, resulting in a mixed texture at the completion of recrystallization. The coherent Σ3 boundaries between the new components stabilized their growth through consuming the other oriented crystals separated by random high-angle boundaries. When sintered into bulk, the texture of the Cu was dominated by the orientations of the abnormally grown grains. The effects of GNSs on the recrystallization of Cu foils were also Cu foil thickness dependent. For the 10 μm thick foils, the effect of the GNSs manifested after the samples were sintered to high temperatures (> 700 ℃). Instead of creating much constraint to the expansion of the adjacent Cu foils, the GNSs worked as a barrier preventing the penetration of the grown Cu grains, resulting in the stabilization of the recrystallization texture represented by the two rotated components. For the Cu/GNS composite with Cu foil thickness of 30 μm, the results evidenced that a strong Cube orientation was produced in the Cu/GNS composite instead of the individual non-Cube orientations in the pure Cu stack without GNSs. Detailed strain-state analysis of the Cu foils in the Cu/GNS composite revealed that the anisotropic expansion behavior of the GNS that is incompatible with that of the Cu foils imposed multiple elastic constraints to the foils, resulting in a biaxial isostrain state in the surface layers and a uniaxial compressive strain state in the central layer. The elastic anisotropy of Cu favors the growth of the Cube oriented grains to minimize the total strain energy. The results of the present work provide quantitative and detailed information on recrystallization of thin Cu foils and laminated composite, which contributes to deepening the understanding of recrystallization behaviour of 2D materials. The mechanisms revealed are useful for analysing abnormal grain growth in elastically strained materials and can also be applied to fabrication process for texturization or even monocrystallization.; La recristallisation est le processus des métaux déformés à froid qui se produit lors du traitement thermique. La texture de recristallisation contribue à l'anisotropie des propriétés mécaniques et physiques. Motivés par la minimisation des produits, les matériaux 2D et les composites stratifiés sont de plus en plus demandés pour des applications. Ainsi, à des fins scientifiques et techniques, des recherches sur la recristallisation de tels matériaux sont nécessaires pour comprendre les mécanismes sous-jacents. Dans ce travail, des feuilles de Cu et des composites stratifiés à matrice de Cu renforcé de nanofeuilles de graphène (GNS) avec des épaisseurs de Cu de 10 μm et 30 μm ont été fabriqués. La recristallisation a été étudiée de l'échelle microscopique à l'échelle macroscopique par SEM-EBSD pour l'observation de microstructure, rayonnement neutronique et synchrotron pour l'analyse de texture et rayonnement synchrotron in situ pour l'évaluation de la déformation du réseau. Les données obtenues ont été analysées dans le cadre de la cristallographie combinée à l'élasticité et à l'énergie de surface. Les résultats ont montré que le comportement de recristallisation de Cu était grandement affecté par l'épaisseur de la feuille de Cu et l'ajout des GNSs. Pour les feuilles de Cu de 10 μm sans GNSs, elles ont subi une transition de la texture de laminage à froid à une texture de recristallisation dominée par des composants Cube tourné RD et Copper tourné φ2. La transition a été contrôlée par des facteurs intrinsèques microstructuraux et extrinsèques géométriques d'échantillons. Les orientations des germes sont héritées des orientations de déformation. Ceux avec des facteurs de Taylor faibles (Cube, Goss et Brass) ont montré une préférence de taille. La croissance post-nucléation a été affectée par la contrainte d'élasticité thermique biaxiale et l'énergie de surface. En raison de leurs effets opposés, les orientations ayant des modules biaxiaux et une densité d'énergie de surface modérés (S, Copper, Brass et composants de recristallisation) ont survécu, résultant en une texture mixte à la fin de la recristallisation. Les joints Σ3 cohérents entre les nouvelles composantes ont stabilisé leur croissance en consommant les autres séparés par des joints aléatoires à grand angle. Une fois le Cu fritté en masse, sa texture était dominée par les orientations des grains à croissance anormale. Les effets des GNSs sur la recristallisation des feuilles de Cu dépendaient également de l'épaisseur de la feuille de Cu. Pour les feuilles de 10 μm d'épaisseur, l'effet des GNSs se manifeste après le frittage des échantillons à des températures élevées (> 700 ℃). Au lieu de créer beaucoup de contraintes à l'expansion des feuilles de Cu adjacentes, les GNSs ont fonctionné comme une barrière empêchant la pénétration des grains de Cu développés, entraînant la stabilisation de la texture de recristallisation représentée par les deux composantes tournées. Pour le composite Cu/GNS avec une épaisseur de Cu de 30 μm, les résultats ont montré qu'une forte orientation Cube était produite dans le composite Cu/GNS au lieu des orientations individuelles non Cube dans l'empilement de Cu pur sans GNSs. Une analyse détaillée de l'état de déformation de Cu dans le composite Cu/GNS a révélé que le comportement d'expansion anisotrope du GNS qui est incompatible avec celui de Cu imposait de multiples contraintes élastiques aux feuilles, entraînant un état isocontrainte biaxiale dans la couche en surface et un état de déformation en compression uniaxiale dans la couche centrale. L'anisotropie élastique du Cu favorise la croissance des grains orientés Cube pour minimiser l'énergie totale de déformation. Les résultats du présent travail fournissent des informations quantitatives détaillées sur la recristallisation de feuilles de Cu et de composites stratifiés, ce qui contribue à approfondir la compréhension du comportement de recristallisation des matériaux 2D.

Texte intégral accessible uniquement aux membres de l'Université de Lorraine jusqu'au 1er avril 2020.; A thorough investigation has been conducted on the Ti-7333 alloy in terms of the β to α phase transformation. It was revealed that the structure transformation is realized by a contraction in the β, an elongation in the β and β, and a shear on the {1"1" ̅"2" ̅}ββ slip system. Each α precipitate is composed of two kinds of nano-sized α domains. One is situated on the broad face of the major α precipitate (named interface α), and the other goes through the major α (termed penetrating α). The nucleation of such α is induced by the large shear strain generated by the formation of the major α. The penetrating α does not obey the BOR with the β matrix. The nucleation of such α is induced by the largest normal strain generated by the formation of the main α plate. The selection of the α variants during hot deformation at 700°C happens with dependence on the local crystal perfection of the β grains. In the slightly deformed β grains, 2 BOR variants are formed ‘cross-shaped’ clusters. The selected variants make maximum contribution to the macroscopic deformation and receive the maximum resolved shear stress from the external load resolved on their {1"1" ̅"2" ̅}ββ systems for transformation. In the heavily deformed β grains occupied mainly by dislocation slip, 2 to 4 BOR variants are selected in smaller numbers. The selection criterion is still obeyed but with restriction from the local deformation. The deformation behavior during 700°C compression presents three characteristic stress-strain stages: a linear stage (Stage I), a discontinuous yielding (Stage II) and a steady-state (Stage III). At the end of Stage I, more than 90% of the β boundaries are occupied by grain boundaries α (αGB). The discontinuous yielding of Stage II originated from the fragmentation of the αGB and the intensive formation of mobile dislocations near the β grain boundary areas. The steady-state of Stage III arises from two orientation dependent deformation modes of the β grains. For those in favorable activation orientation for their {110}ββ systems with respect to the external compressive load, the deformation is realized by the dislocation slip and by the formation of slip bands; whereas for those with their {1"1" ̅"2" ̅}ββ systems - the system for β to α transformation - in favorable orientations, the deformation is achieved by intensive formation of intragranular α precipitates.; Une étude approfondie a été menée sur l’alliage Ti-7333 en termes de transformation de phase β en α. Il a été montré que la transformation de la structure est réalisée par une contraction dansβ, un allongement dans β et β, et un cisaillement sur le système de glissement{1"1" ̅"2" ̅}ββ. Chaque précipité α est composé de deux types de domaines α de taille nanométrique. L'un est situé sur la face large du précipité α majeur (interface α), l'autre traverse le α majeur (α pénétrant). La nucléation de cet α est induite par la contrainte importante de cisaillement générée par la formation du α majeur. Le α pénétrant n'obéit pas au BOR avec la matrice β mais. La nucléation de cet α est induite par la plus grande contrainte normale générée par la formation de la plaque α principale. La sélection des variantes α lors de la déformation à chaud à 700 °C s'effectue en fonction de la perfection cristalline locale des grains β. Dans les grains β légèrement déformés, 2 variantes de BOR liées. Les variantes sélectionnées apportent une contribution maximale à la déformation macroscopique et subissent la contrainte de cisaillement résolue maximale de la charge externe résolue sur leurs systèmes de transformation {1"1" ̅"2" ̅}ββ. Dans les grains β fortement déformés occupés principalement par des bandes de glissement, 2 à 4 variantes de BOR sont sélectionnées. Le critère de sélection est toujours respecté mais avec une restriction de la déformation locale. Le comportement en déformation lors de la compression à 700 °C présente trois stades contraintes-déformations caractéristiques : un stade linéaire (stade I), un stade d’écoulement discontinu (stade II) et un stade stable (stade III). À la fin du stade I, plus de 90% des joints de grains β sont occupés par des joints de grains α (αGB). Le rendement discontinu du stade II provient de la fragmentation de αGB et de la formation intensive de dislocations mobiles près des joints de grains β. L'état d'équilibre du stade III résulte de deux modes de déformation. Pour ceux dont l'orientation d'activation est favorable pour leurs systèmes {110}ββ par rapport à la charge de compression, la déformation est réalisée par le glissement de dislocation et par la formation de bandes de glissement; alors que pour ceux avec leur {1"1" ̅"2" ̅}ββ systèmes - le système de transformation de β à α - dans des orientations favorables, la déformation est obtenue par formation intensive de précipités α intragranulaires.

Texte intégral accessible uniquement aux membres de l'Université de Lorraine jusqu'au 1er avril 2020.; A thorough investigation has been conducted on the Ti-7333 alloy in terms of the β to α phase transformation. It was revealed that the structure transformation is realized by a contraction in the β, an elongation in the β and β, and a shear on the {1"1" ̅"2" ̅}ββ slip system. Each α precipitate is composed of two kinds of nano-sized α domains. One is situated on the broad face of the major α precipitate (named interface α), and the other goes through the major α (termed penetrating α). The nucleation of such α is induced by the large shear strain generated by the formation of the major α. The penetrating α does not obey the BOR with the β matrix. The nucleation of such α is induced by the largest normal strain generated by the formation of the main α plate. The selection of the α variants during hot deformation at 700°C happens with dependence on the local crystal perfection of the β grains. In the slightly deformed β grains, 2 BOR variants are formed ‘cross-shaped’ clusters. The selected variants make maximum contribution to the macroscopic deformation and receive the maximum resolved shear stress from the external load resolved on their {1"1" ̅"2" ̅}ββ systems for transformation. In the heavily deformed β grains occupied mainly by dislocation slip, 2 to 4 BOR variants are selected in smaller numbers. The selection criterion is still obeyed but with restriction from the local deformation. The deformation behavior during 700°C compression presents three characteristic stress-strain stages: a linear stage (Stage I), a discontinuous yielding (Stage II) and a steady-state (Stage III). At the end of Stage I, more than 90% of the β boundaries are occupied by grain boundaries α (αGB). The discontinuous yielding of Stage II originated from the fragmentation of the αGB and the intensive formation of mobile dislocations near the β grain boundary areas. The steady-state of Stage III arises from two orientation dependent deformation modes of the β grains. For those in favorable activation orientation for their {110}ββ systems with respect to the external compressive load, the deformation is realized by the dislocation slip and by the formation of slip bands; whereas for those with their {1"1" ̅"2" ̅}ββ systems - the system for β to α transformation - in favorable orientations, the deformation is achieved by intensive formation of intragranular α precipitates.; Une étude approfondie a été menée sur l’alliage Ti-7333 en termes de transformation de phase β en α. Il a été montré que la transformation de la structure est réalisée par une contraction dansβ, un allongement dans β et β, et un cisaillement sur le système de glissement{1"1" ̅"2" ̅}ββ. Chaque précipité α est composé de deux types de domaines α de taille nanométrique. L'un est situé sur la face large du précipité α majeur (interface α), l'autre traverse le α majeur (α pénétrant). La nucléation de cet α est induite par la contrainte importante de cisaillement générée par la formation du α majeur. Le α pénétrant n'obéit pas au BOR avec la matrice β mais. La nucléation de cet α est induite par la plus grande contrainte normale générée par la formation de la plaque α principale. La sélection des variantes α lors de la déformation à chaud à 700 °C s'effectue en fonction de la perfection cristalline locale des grains β. Dans les grains β légèrement déformés, 2 variantes de BOR liées. Les variantes sélectionnées apportent une contribution maximale à la déformation macroscopique et subissent la contrainte de cisaillement résolue maximale de la charge externe résolue sur leurs systèmes de transformation {1"1" ̅"2" ̅}ββ. Dans les grains β fortement déformés occupés principalement par des bandes de glissement, 2 à 4 variantes de BOR sont sélectionnées. Le critère de sélection est toujours respecté mais avec une restriction de la déformation locale. Le comportement en déformation lors de la compression à 700 °C présente trois stades contraintes-déformations caractéristiques : un stade linéaire (stade I), un stade d’écoulement discontinu (stade II) et un stade stable (stade III). À la fin du stade I, plus de 90% des joints de grains β sont occupés par des joints de grains α (αGB). Le rendement discontinu du stade II provient de la fragmentation de αGB et de la formation intensive de dislocations mobiles près des joints de grains β. L'état d'équilibre du stade III résulte de deux modes de déformation. Pour ceux dont l'orientation d'activation est favorable pour leurs systèmes {110}ββ par rapport à la charge de compression, la déformation est réalisée par le glissement de dislocation et par la formation de bandes de glissement; alors que pour ceux avec leur {1"1" ̅"2" ̅}ββ systèmes - le système de transformation de β à α - dans des orientations favorables, la déformation est obtenue par formation intensive de précipités α intragranulaires.