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Materials science and engineering / A 754, 562 - 568 (2019). doi:10.1016/j.msea.2019.03.073, A discontinuous yielding was observed in the as-extruded Mg-7Gd-2Y-1Zn-0.6Zr (wt. %) alloy under uniaxial tension along the extrusion direction, which was eliminated by the peak-aging treatment. The deformation mechanisms of the as-extruded and peak-aged alloys were studied by in-situ synchrotron diffraction measurement and elastic-viscoplastic self-consistent (EVPSC) modeling. The in-situ synchrotron diffraction results suggest that the unpinning of basal dislocations from solute atmospheres causes the stress relaxation in the basal slip favored grains. The EVPSC modeling results indicate that the discontinuous yielding in the as-extruded alloy is associated with the interaction between basal dislocations and solute atmospheres. After peak-aging treatment, the interaction between basal dislocations and solute atmospheres is weakened due to the consumption of a number of solute atoms. Consequently, the discontinuous yielding is eliminated in the peak-aged alloy., Published by Elsevier, Amsterdam

A low carbon steel was processed by Cold Rolling (CR) and Asymmetrical Rolling (ASR) at room temperature until 200 µm thickness reduction using multiple rolling passes of 25 µm. ASR process induced a soft curvature with a 45.7 mm length and 128.8 mm radius, while the CR process did not show any curvature. Materials showed differences in the strain path as well as in the texture and microstructure evolution, not only concerning the mode of deformation but also across the sheet thickness. The hardness and tensile tests indicated a higher strength after processing by ASR than CR for the same thickness reduction. Changes in dislocation densities and grain size were more pronounced in the surface neighborhoods of the material processed by ASR than the as-received (AR) and CR conditions, while the grain size and the dislocation densities of the CR material were more homogeneous across the sheet thickness. Synchrotron measurements allowed to build dislocations and crystal size distribution functions. These functions demonstrated that for the surface zones for ASR condition, high dislocation densities correspond to the grains developing rolling texture components. In contrast, the highest dislocations densities for the center zone formed inside the smallest crystals with shear texture orientations. By ASR, a heterogeneous material with hard surfaces was generated using multiple small thickness reductions in a narrow and thick sheet. In contrast, with CR, a homogeneous hardness increase was obtained throughout the sheet's thickness, avoiding curvature in the material. It was found that high and heterogeneous distributions of geometrically necessary dislocations (GNDs) across the sheet thickness were responsible for the ASR material additional hardening.

Materials characterization 176(111132), 1-14 (2021). doi:10.1016/j.matchar.2021.111132, The interplay of microstructural mechanisms controlling the deformation-induced martensitic phase transformationsand the texture formation in all phases of a metastable austenitic Cr-Mn-Ni steel was investigatedusing in situ synchrotron radiation diffraction under uniaxial compression and ex situ electron backscatterdiffraction. With increasing deformation, the originally fully austenitic steel transformed to a mixture ofγ-austenite, ε-martensite and α´-martensite. The face centred cubic γ-austenite formed a fibre texture {110} withrespect to the deformation direction. The texture degree increased progressively with increasing deformation.The hexagonal close packed ε-martensite was preferentially oriented with the reciprocal direction {1013} alongthe load axis. The texture degree was nearly independent of the deformation extent. The body centredα´-martensite formed a mixed texture {100} & {111} along the deformation direction. The texture component{100} was very strong in the early stages of the α´-martensite formation, but it deteriorated with increasingdeformation. The texture evolution is explained by the competition between the transformation texture, severaldeformation-induced mechanisms, which are highly sensitive to the local orientation of the grains with respect tothe acting force, like the stacking fault formation and martensitic transformation in austenite, and the variantselection in both martensites and the twinning of α´-martensite., Published by Science Direct, New York, NY

Materials characterization 175, 111044 (1-12) (2021). doi:10.1016/j.matchar.2021.111044, Texture modification during sheet rolling appears differently in binary Mg-RE (rare-earth) or Mg-Ca alloy, compared to their ternary counterparts containing Zn. The differences in texture development and the active deformation mechanisms under tensile loading were investigated in the binary alloys. These analyses are based on in-situ synchrotron experiments and electron backscatter diffraction measurements to reveal direct experimental evidence of the texture development and the active deformation mechanisms. Higher activations of nonbasal < a > and pyramidal < c+a > dislocations were found in the Nd or Ca containing Mg alloys, compared to the Mg-Zn alloy. The texture development shows an obvious feature, which is a broadening of the basal pole intensity distribution perpendicular to the loading direction and a strengthening of the pole at the loading direction in all examined sheets. This texture development relates to the higher activation of prismatic < a > slip. The addition of Zn in the Mg-RE or Mg-Ca alloys further promotes the activation of nonbasal < a > and pyramidal < c+a > dislocations. This enhanced prismatic < a > slip in the Zn containing ternary alloys is confirmed by EBSD misorientation analysis., Published by Science Direct, New York, NY

Materials characterization 159, 110039 - (2020). doi:10.1016/j.matchar.2019.110039, Understanding of the deformation micro-mechanism as a function of grain orientation during cyclic loading is ofsignificant importance to have failure safe design of structural components made of commercially pure titanium(CP-Ti). The evolution of deformation microstructure and texture of commercially pure titanium samples withprismatic-pyramidal (orientation A) and near basal (orientation B) as initial texture along the loading directionhas been investigated during load reversal at±8% and ± 12% strain using in-situ synchrotron X-ray diffraction.The synchrotron X-ray diffraction results have been further complemented with Elastic-Plastic Self-Consistent (EPSC) simulation of the texture data and ex-situ Electron backscatter diffraction (EBSD) scan taken atthe same region. Orientation A showed partially reversible texture whereas orientation B showed non-reversibletexture with mechanical reversibility. The partial textural reversibility has been attributed to the prism to basalslip transition which toggles the c-axis between the normal and transverse direction during the tension-compressioncycle. With an increase in strain from 8 to 12%, microstrain and dislocation density in the basal plane oforientation A decreases sharply. On the other hand, for the same level of strain in orientation B, microstrainincreases but the dislocation density of basal plane shows insignificant change. The crystal orientation mapobtained from ex-situ EBSD of deformed microstructure complements to the fact indicating, with increase instrain, deformation of basal oriented grains show non-Schmid behaviour of contraction twin propagation due tolocal strain incompatibility in orientation A. On the other hand, the prism oriented grains of orientation B havemostly deformed by extension twinning, which reorients them towards basal orientation. The deformationproceeds by lateral thickening of twins due to the lower elastic stiffness of the twinned region compared to thegrain matrix. The extension twin boundaries get converted to contraction twin boundaries at higher strain duringload reversal., Published by Science Direct, New York, NY

In this study, high energy synchrotron radiation was used to perform an in-situ diffraction experiment in medium Mn Fe-6Mn-0.5C-1Al alloy to study the elemental partitioning and consequent austenite phase evolution at different stages, namely, during heating, holding and cooling. It has been observed that the austenite phase fraction significantly increases on annealing at the inter-critical annealing temperature and remains stable at room temperature. The austenite phase stability at room temperature is due to the rapid partitioning of manganese (Mn) and carbon (C) during annealing. The relative change in d-spacing (Δd/d) during heating-cooling confirms the partitioning of alloying elements during inter-critical annealing.

The microstructural characteristics of deformation-processed materials highly influence their mechanical properties. For a complete characterization of a microstructure both local and global information must be gathered, which requires the combination of different analysis techniques. X-ray and Electron Backscatter Diffraction were used in the present paper to characterize the deformation induced in a cold rolled F138 austenitic stainless steel sample. The results obtained using laboratory and synchrotron X-ray sources were compared and combined with EBSD quantitative results, allowing the global and local characterization and orientation dependence of the deformation microstructure. A particular behavior was observed in the XRD data corresponding to the planes with < 220 >∥ ND, likely due to a smaller amount of defects accumulated in the crystals with that particular orientation. EBSD was used to separate the scans data into partitions and to calculate misorientation variables and parameters, showing that this behavior can be attributed to a combination of larger grain sizes, lower local boundary misorientations and dislocation densities for crystals having < 220 >∥ ND. Several conclusions, of general validity for the evaluation of microstructure anisotropy, can be extracted from the results. Fil: de Vincentis, Natalia Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Avalos, Martina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Benatti, Emanuel Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Kliauga, A.. Universidade Federal do São Carlos; Brasil Fil: Brokmeier, H. G.. Institut für Werkstoffkunde und Werkstofftechnik; Alemania Fil: Bolmaro, Raul Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina

Equal channel angular pressing was carried out on Al–Mg alloys to study the effect of Mg addition on the microstructure, texture and strength after severe plastic deformation by 8 passes of equal channel angular pressing (ECAP) through route Bc. The increase in Mg content enhanced the propensity of continuous dynamic recrystallization and simultaneously decreased the average grain size of the alloy. The microstructure and local texture was heterogeneous across the billet thickness for all the samples, irrespective of composition. All the samples showed a shear-type bulk texture generally observed in face-centred cubic metals with strong BE/‾BE components. The weakening of the texture with increase in Mg content is attributed to the substructure evolution during the ECAP process. The grain size and dislocation density have been determined by X-ray diffraction line profile analysis. The experimentally determined yield strength of the ultrafine grained samples can be explained by a combination of solid solution, dislocation and grain size strengthening, the latter being predominant.

High precision dimensionality tubes are required for a number of applications. Nevertheless, there are some troubles and challenges to produce high quality tubes in a cost-effective way. In recent works done at the Institute of Metallurgy at Clausthal University of Technology, the tube drawing process was optimized by introducing dynamic tilting and shifting of the die. These methods made it possible to control the wall-thickness variation and even residual stresses (RSs) evolution. A possible influence on texture evolution, however, has not yet been investigated, though it is well known that the crystallographic texture has a remarkable effect on materials' properties. Furthermore, the initial texture clearly influences the microstructural evolution during plastic deformation, affecting the RSs evolution and dimension accuracy, too. In this paper the evolution and heterogeneity of the texture are introduced for tube drawing performed with a tilted die. The measurements were done using synchrotron and neutron diffraction methods. The aim was to understand the behavior of the material during the asymmetrical tube drawing, caused by the tilted die, and connect the effects between eccentricity and residual stresses. Pole figures and ODF densities were studied and the creation and variation of different texture components were analyzed as well.

High energy synchrotron radiation was used to perform an in-situ diffraction experiment in medium Mn Fe-6Mn-0.5C-1Al alloy to study the elemental partitiong and austenite phase evolution at different heating, holding and cooling stages. It has been observed that austenite phase fraction increases at inter-critical annealing temperature significantly and it remains stable at room temperature. Austenite phase stability at room temperature is due to rapid partitioning of Mn and C during annealing. The relative change in d-spacing (Δd/d) during heating-cooling indicates partitioning of alloying elements during inter-critical annealing.

Materials science and engineering / A Structural materials : properties, microstructure and processing properties, microstructure and processing 782, 139187 - (2020). doi:10.1016/j.msea.2020.139187, The present study aims to understand the evolution of textural and microstructural heterogeneity and its effect on evolution of mechanical properties of an equiatomic FCC CoCuFeMnNi high entropy alloy (HEA) disc subjected to high pressure torsion (HPT). HPT was performed on disc specimen with a hydrostatic pressure of 5 GPa for 0.1, 0.5, 1 and 5 turns at room temperature where the hardness saturated at 1941 MPa at the periphery of the sample after five turns. Synchrotron diffraction texture analysis of five-turn HPT sample reveals characteristic shear texture with the dominance of A and A* components near central region of the disc and it shifts to C {001} component near the periphery of the disc. X-ray diffraction analysis shows decrease in crystalline size with simultaneous increase in dislocation density for five-turn HPT sample with increasing strain from centre to the periphery of the disc. Microstructural analysis using electron back scatter diffraction and transmission electron microscopy indicates extensive grain fragmentation (≈55 nm) at the periphery of five-turn sample. The evolution of hardness from centre to the periphery of the disc cannot be explained only on the basis of evolution of grain size and dislocation density. The increase in contribution from solid solution strengthening due to partial dissolution of copper rich nano-clusters is expected to be the underlying cause for increase in the hardness. Thus, evolution of gradient microstructure, texture, and chemistry opens up new vistas for designing functionally graded materials for engineering applications., Published by Elsevier, Amsterdam

The dislocation density evolution along the loading axis of a textured AA 7020-T6 aluminum alloy during uniaxial tension was investigated by in-situ synchrotron diffraction. The highly parallel synchrotron beam at the High Energy Materials Science beamline P07 in PETRA III, DESY, offers excellent conditions to separate different influences for line broadening from which micro-strains are obtained using the modified Williamson–Hall method which is also for defect density investigations. During tensile loading the dislocation density evolution was documented from the as-received material (initial micro-strain state) to the relaxation of the strains during elastic deformation. After yield, the increasing rate of dislocation density growth was relatively fast till half-way between yield and UTS. After that, the rate started to decrease and the dislocation density fluctuated as the elongation increased due to the generation and annihilation of dislocations. When dislocation generation is dominant, the correlation between the flow stress and dislocation density satisfies the Taylor equation. Besides, a method to correct the thickness effect on peak broadening is developed in the present study.

The microstructure developed during severe plastic deformation results in improved mechanical properties because of the decrease in domain sizes and accumulation of defects, mainly dislocation arrays. The characteristic deformation stages observed in low stacking fault energy (SFE) face centered cubic (FCC) materials are highly influenced by the development of the primary and secondary twinning that compete with dislocation glide. In this paper, a low SFE F138 stainless steel is deformed by equal channel angular pressing (ECAP) up to 4 passes at room temperature (RT) and at 300°C to compare the grain refinement and twin boundary development with increasing deformation. Tensile tests were performed to determine the deformation stages reached by the material before and after ECAP deformation, and the resulting microstructure was observed by TEM. X-ray diffraction and EBSD, average technique the first and local the second one, were used to quantify the microstructural changes, allowing the determination of diffraction domain sizes, dislocation and stacking fault densities and misorientation indices, which lead to a complete analysis of the deformation introduced in the material, with comparative correlations between various microstructural parameters. Fil: de Vincentis, Natalia Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Kliauga, A.. Universidade Federal do São Carlos; Brasil Fil: Ferrante, M.. Universidade Federal do São Carlos; Brasil Fil: Avalos, Martina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Brokmeier, H. G.. Institut für Werkstoffkunde und Werkstofftechnik; Alemania Fil: Bolmaro, Raul Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina

The materials science neutron diffractometer STRESS-SPEC located at FRM II is a dedicated instrument for strain and pole figure measurements. Both methods make complementary demands on sample handling. On one hand pole figure measurements need a high degree of freedom to orient small samples and on the other hand in strain investigations it is often necessary to handle large and heavy components. Therefore a robot based sample positioning system was developed, which has the capability to provide both possibilities. Based on this new robot system further developments like a full automated sample changer system for texture measurements were accomplished. Moreover this system opens the door for combined strain and texture analysis at STRESS-SPEC.

The effect of magnetic annealing on crystallographic texture, microstructure, defects density and magnetic properties of a Fe-2.6% Si steel has been analyzed. After two stage cold rolling (75% and 60% cold rolled) with intermediate annealing process at (600 °C/1 h) the sample annealed at 600 °C for one hour during which different magnetic field of 0, 7 and 14 T were applied has been investigated. The effect of defects density after cold rolling process on the recrystallization texture and magnetic properties was characterized. Heat treatments under a high external field of 14 T show a drastic improvement of the magnetic properties such as significantly increased permeability. Neutron diffraction measurements were preferred for measurement of the bulk sample texture so that sufficient grain statistics were obtained. Because of its small wavelength (0.05–0.2 A) Synchrotron diffraction with high photon energy was used to evaluate the defects density by a modified Williamson–Hall plot.

Materials science and engineering / A 726, 143 - 153 (2018). doi:10.1016/j.msea.2018.04.036, Synchrotron X-ray diffraction technique has been used to estimate defect structure in terms of dislocationdensity, crystallite size and micro-strain in commercially pure titanium subjected to tension and cyclic deformationin stress and strain control mode. Statistical analysis of micro-texture data collected from electronbackscatter diffraction approximately from the same region as that of synchrotron X-ray has been used to correlateorientation dependent micro-strain and dislocation density with deformation microstructure and microtexture.Two different orientations, namely, A with prismatic-pyramidal and B with basal orientation along theloading axis has been considered. Weak initial texture yet significant anisotropy in hardening/softening responseand failure mode for monotonic tension and cyclic loading paths has been observed. Higher strain hardeningresponse of orientation A during monotonic tensile deformation can be attributed to the evolution of lowermicro-strain on basal orientation grains i.e, 〈0002〉ǁND along with extensive multi-variant twinning that alsorestricts crack propagation and delays failure in stress control mode. On the other hand, in strain control mode,orientation B shows higher fatigue life due to the generation of lower micro-strain in the basal orientation grainsand single variant twinning that can undergo detwinning easily is responsible for delayed crack nucleation andsubsequent failure., Published by Elsevier, Amsterdam

Severe Plastic Deformation (SPD) techniques are widely used nowadays because of the mechanical properties improvements caused by grain refinement and development of dislocation arrays. Diffraction techniques can be used to assess the changes registered in the microstructure through these methods. Two sets of samples of F138 austenitic stainless steel were analyzed in this paper: one set was deformed by ECAE up to two pressings at room temperature, and the other set was cold rolled to 70% reduction and annealed at 600, 700, 800 and 900 °C for 1 h. The microstructural changes were determined using X-Ray diffraction and EBSD, combining both, global and local information and characterizing domain sizes, dislocation and stacking fault densities and misorientation degree and distribution caused by the different thermomechanical processing. It was observed that, despite cold rolling and 2 ECAE passes rendered rather similar von Mises deformations, the microstructure through each deformation method was different: 2 ECAE passes seem to be more effective for grain refinement and generation of equiaxed domains than cold rolling. The more significant twin activation observed in the former sample, because of continuous strain path change, may explain the difference, although dislocation densities and mechanical properties did not differ substantially for both deformation methods. Fil: de Vincentis, Natalia Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Avalos, Martina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Kliauga, A.. Universidade Federal do São Carlos; Brasil Fil: Brokmeier, H. G.. Institut für Werkstoffkunde und Werkstofftechnik; Alemania. Helmholtz Zentrum Geesthacht; Alemania Fil: Bolmaro, Raul Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina

Microstructural characterization by combined EBSD and X-ray diffraction analysis is shown for an FCC material deformed by rolling and further heat treatment on air. The wide variety of x-rays sources combined with EBSD allows some correlations between microstructural parameters to be withdrawn by carefully analyzing x-ray peak broadening. The combination of both techniques provides a deeper understanding of anisotropic accumulation of dislocation arrays on a deformed F 138 stainless steel. The anisotropy results in a smaller peak breadth for crystal orientations with [110] planes contained on the rolling plane, further explained as resulting from a lower storage of dislocations. After heat treatment the effect is reverted and the formerly less misoriented orientations become more uniformly oriented revealing a faster dislocation migration and annihilation and/or trapping Behandelt wird die mikrostrukturelle Charakterisierung mittels kombinierter EBSD- und Röntgenbeugungsanalyse für einen durch Walzen und Wärmebehandlung an Luft verformten kfz-Werkstoff. Die Kombination eines breiten Spektrums an Röntgenquellen und EBSD ermöglicht auf der Grundlage einer sorgfältigen Analyse der Röntgenpeakverbreiterung die Ableitung einiger zwischen mikrostrukturellen Parametern bestehenden Korrelationen. Die Kombination beider Techniken sorgt für ein tieferes Verständnis der anisotropen Ansammlung von Versetzungsanordnungen in rostfreiem Stahl F 138. Aus der Anisotropie ergibt sich eine geringere Peakbreite für in der Walzebene enthaltene Kristallorientierungen mit [110]-Ebenen, die auch als Folge einer geringeren Einlagerung an Versetzungen erklärt werden kann. Nach der Wärmebehandlung kommt es zu einer Umkehrung des Effekts und die zuvor wenig fehlorientierten Ausrichtungen richten sich einheitlicher aus und weisen eine schnellere Versetzungswanderung und -annihilation und/oder Trapping (etwa: „Einfangen“) auf Fil: Bolmaro, Raul Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Avalos, Martina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: de Vincentis, Natalia Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Kliauga, Andrea M.. Federal University of São Carlos; Brasil Fil: Brokmeier, Heinz Günter. Institut für Werkstoffkunde und Werkstofftechnik; Alemania

This article reports on the development of the rotational friction welding process for the welding of γ-TiAl- casting alloy Ti-47Al-3.5(Mn+Cr+Nb)-0.8(B+Si) to Ti6Al4V base metal and on the characterisation of the mechanical and microstructural properties of dissimilar metal friction welding. Pre- and post welding heat treatment is necessary in order to reduce the occurrence of bonding defects. The mechanical behaviour of friction welded joints under tensile loading at room temperature is primarily determined by the properties of the inter-metallic γTiAl- casting alloy base metal and not by the bonding zone itself. At the relevant service temperature of 700 °C, failure by fracture does not take place on the Ti6Al4V side of the dissimilar metal friction welded joint due to the super-plastic deformation of this alloy.

The austenitic stainless steel X5CrNiMo17-12-2 in thickness ranging from 0.2 mm to 1.0 mm was examined in regard to the mechanical properties and microstructure. The aim was to investigate the suitability of conventional test methods for thin material down to 0.2 mm. Within these investigations, all used thicknesses were characterized by conventional tensile tests and X-ray diffraction. The results were subsequently compared with each other. The material specific vertical anisotropy r and forming limit curve showed a strong dependence on material thicknesses. The results of anisotropy pointed out different values depending on the test methods performed. In addition, the results of microstructure analysis show a decrease of grain size with lower material thickness caused by the formation of twins and probably heat treatments during the manufacturing process.

Seminar, 中国; Materials and design 170, 107705 (2019)., In thiswork, the tension-compression asymmetry of an extrudedMg-8.4wt.%Gd-2.3wt.%Y-0.2wt.%Zr alloywith a bimodal microstructure, consisting of fine DRXed grains and coarse unDRXed grains, was investigated by in-situ synchrotron diffraction testing and microstructure analysis. It is found that the as-extruded alloy exhibits good tension-compression yielding symmetry, which is attributed to the same deformation mechanisms (prismatic and basal slip) governing the tensile and compressive yielding. However, the strain hardening response after the macroscopic yielding is different under tension and compression, since tensile twinning,whichmainly occurs in the unDRXed grains, makes an important contribution to the deformation under compression, but not under tension. The alloy shows a somewhat linear strain hardening after yielding under compression, which is mainly due to the inhibition of tensile twinning and enhancement of prismatic slip. The suppression of tensile twinning mainly results from the high concentration of rare earth solute elements, weak texture and grain refinement of the DRXed regions. This work suggests that the tension-compression asymmetry of Mg alloys can be effectively reduced by the addition of rare earth elements and grain refinement., Published by Elsevier Science, Amsterdam [u.a.]

Residual stress evaluation is an important stage to interpret the fatigue behavior of many engineering materials. The present research aimed at evaluating non-destructively the macroscopic compressive and balancing tensile residual stresses generated in the surface layer and in the core region, respectively, in mechanically surface treated alpha titanium alloy Ti–2.5Cu. In order to achieve that purpose, a combination of energy-dispersive X-ray and neutron diffraction was used. Results revealed that the zero-crossing depths (where the residual stress value of zero is reached) and balancing tensile residual stress distributions in the core region were well defined.

The Mg/Al laminated composites were prepared by the accumulative roll bonding (ARB) at ambient temperature using the commercial pure magnesium and pure Al sheets as starting materials. Microstructure of both Mg and Al layer were refined during ARB processing. Neutron diffraction was employed to investigate the texture evolution of this kind of laminated composite. Both the Mg and Al layer of the primary sandwich exhibited dominant shear texture. During the following accumulative roll bonding, the texture of Mg layer transformed to typical rolling texture while the Al layer showed a combined texture type including evident β fiber and the Rotate Cube component.

Rotary friction welding (RFW) was used in the current study to join the dissimilar metals AA7020-T6 aluminium alloy and 316L steel. Neutron diffraction was performed to investigate the texture gradient around the weld line and to map the residual stress over the whole specimen. The texture analysis showed a weak shear component near the bond line of AA7020-T6-T6 side which indicated a plastic deformation of AA7020-T6 during welding. The shear bands were also observed in optical microstructures. Relatively high tensile residual stresses were observed near the bond line on the AA7020-T6 side, which were in-homogeneously distributed from the perimeter to the rod centre, while high compressive residual stresses were found in the sample centre at the bond line in the 316L steel.

Equal channel angular pressing (ECAP) was performed on the as-extruded commercial pure magnesium at 250 °C for 4 passes. The internal friction of the ECAPed pure Mg as a function of strain amplitude was investigated by dynamic mechanical analyzer (DMA), and the cyclic microplasticity of pure Mg was investigated by tensile loading and unloading test. After ECAP processing, the grain size is significantly refined, the texture component with basal planes parallel to extrusion direction is replaced by a new stronger one with basal planes having a tilting angle of about 40° to the extrusion direction. The stress in microplastic region is reduced with increasing ECAP passes, while the internal friction increases. The internal friction of Mg at high strain amplitude is closely related to microplastic deformation and can be interpreted by dislocation mechanism. The Granato and Lucke model only satisfies in anelastic regions, while the internal friction in microplastic deformation region should be explained in terms of the internal friction model postulated by Peguin. The internal friction related to microplasticity can be divided into two parts with different activation volumes of dislocation motion, which correspond to the two regions of microplasctic deformation process. The initial stage associated with dislocation motion on basal plane shows larger activation volume and lower friction stress of dislocations. The second stage related to the annihilation and tangle of dislocations is characterized by larger hardening exponent and friction stress.

Bulk texture measurement of multi-axial forged body center cubic interstitial free steel performed in this study using x-ray and neutron diffraction indicated the presence of a strong {101}aOE (c) 111 > single texture component. Viscoplastic self-consistent simulations could successfully predict the formation of this texture component by incorporating the complicated strain path followed during this process and assuming the activity of {101}aOE (c) 111 > slip system. In addition, a first-order estimate of mechanical properties in terms of highly anisotropic yield locus and Lankford parameter was also obtained from the simulations.

Equal channel angular pressing (ECAP) was performed on the extruded commercial pure magnesium at 250 °C for 4 passes. Heat treatments were carried out to modify the microstructures. The cyclic plastic deformation behavior of pure Mg with different grain sizes in microstrain region was studied by tensile loading and unloading experiments. The microplastic deformation process of pure Mg can be divided into two stages. In the first stage, pronounced plastic deformation associated with dislocation motion on basal plane is initiated at several MPa. The materials are softened and characterized by low friction stresses and hardening exponents. The microplastic deformation enters into region II above the strain of about 8 × 10−4. Annihilation and tangle of dislocations lead to the increase of hardening exponents and friction stresses. Pure Mg shows a very pronounced anelastic behavior during cyclic microplastic deformation, which results in a rapid increase of modulus defect, effectively decreasing the elastic modulus by up to 60 %. Grain size has a marked effect on microplastic deformation behavior of pure Mg. With increasing the grain size, the specimen shows a more pronounced microstrain and anelastic behavior.

sAbstract The Mg/Al laminated composites were fabricated by the accumulative roll bonding (ARB) at ambient temperature using the pure magnesium and commercial pure Al sheets. Mg grains were refined after the primary sandwich preparation and then homogenized during the following ARB process while the grain size of Al layer decreased with increasing of the accumulated strains. Both the yield strength and ultimate strength along rolling direction and transverse direction increased gradually while the elongation to failure along both directions decreased with increasing of the ARB cycles. Formation of the Mg 17 Al 12 phase indicated that the ARB process at ambient temperature could lead to a metallurgic bonding of the Mg/Al interface.

Texture gradients are present in most samples, which are due to materials processing. Standard methods to evaluate texture gradients are based on the cut of samples, such as the X-ray investigation of surface textures against the texture inside a sheet. Bulk textures itself averaging over the whole sheet thickness are analysed by thermal neutrons. Both thermal neutrons and photons with high energies allow investigations non-destructively. The beam port Stress-Spec at the Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) at Garching/Germany is equipped with a robot system based on a RX160 Stäubli robot, a Laser Tracker and a heavy basement. Samples up to 30kg can be investigated. Main restrictions are the available neutron flux, the detector efficiency and the detector size. Thus, the gauge volume is restricted to 1x1x1mm for ideal scattering conditions to measure in acceptable time scale. Photons with up to 200keV are known as high brilliant and high intense beam with similar penetration power than thermal neutrons. A typical set up of a high energy beamline for texture gradient investigations works without an Eulerian cradle so that restrictions in handling large sample are of less importance. The HZG materials science beamlines at Doris III and Petra III (Harwi-II@DorisIII and HEMS@PetraIII) are equipped with massif units for sample rotation and x-, y- and z- scanning for samples and additional equipments up to 200kg. Compared to thermal neutrons, which work with wavelengths between 1Å-2.5Å, the wavelength of high energy photons is small (0.05Å – 0.20Å). That leads on one hand to low scattering angles (1° - 10°) and on the other hand to an anisotropic ellipsoidal gauge volume. The local resolution of the synchrotron beam is much better than for thermal neutrons. In both methods corrections for constant gauge volume during pole figure scanning and for anisotropic absorption are of great importance.

In response to the development of new materials and the application of materials and components in advanced technologies, non-destructive measurement methods of textures and residual stresses have gained worldwide significance in recent years. The materials science neutron diffractometer STRESS-SPEC at FRM II (Garching, Germany) is designed to be applied equally to texture and residual stress analyses by virtue of its very flexible configuration. Due to the high penetration capabilities of neutrons and the high neutron flux of STRESS-SPEC it allows a combined analysis of global texture, local texture, strain pole figure and FWHM pole figure in a wide variety of materials including metals, alloys, composites, ceramics and geological materials. Especially, the analysis of texture gradients in bulk materials using neutron diffraction has advantages over laboratory X-rays and EBSD for many scientific cases. Moreover, neutron diffraction is favourable for coarse-grained materials, where bulk information averaged over texture inhomogeneities is needed, and also stands out due to easy sample preparation. In future, the newly developed robot system for STRESS-SPEC will allow much more flexibility than an Eulerian cradle as on standard instruments. Five recent measurements are shown to demonstrate the wide range of possible texture applications at STRESS-SPEC diffractometer.

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.

As a result of the variety of mechanical surface treatments, studies of surface and near-surface characteristics are becoming increasingly important in a variety of industrial fields. This is to achieve more gains by balancing between optimum conditions and costs. In the present study, shot peening (SP), ball-burnishing (BB), laser shock peening (LSP) and ultrasonic shot peening (USP) processes were performed on the α-titanium alloy Ti–2.5Cu after two different heat treatments. The influence of such surface treatments on the surface and near-surface characteristics, such as residual stress, work hardening or dislocation density and surface roughness, was studied. The depth profiles of residual stress and full width at half maximum (FWHM) were obtained by using energy-dispersive X-ray diffraction. Results show that the BB process produced the highest and deepest maximum residual stress and LSP produced the lowest work hardening close to the surface.

Together with the microstructure residual stresses and crystallographic textures are important parameters in considering the application profile of engineering products. Both residual stress and crystallographic texture are related to identical grain arrangements. That means on one hand texture and strain influence each other and on the other hand both informations contribute to considering anisotropic materials properties, quality of welds, inhomogenous behaviour and so on. Non-destructive evaluations need experimental methods going deeply inside a material. Furthermore, it is necessary to handle complex and heavy samples. Neutrons and high-energy X-rays (about 100keV) have a high penetration power in the cm-range to fulfil these requirements. The instrumentation must be very flexible fitting the set-up for both investigations. The materials science diffractometer STRESS-SPEC at the Forschungsneutronenquelle Heinz Mayer-Leibnitz FRM II at Garching/Germany (neutron) and the HZG materials science beamline Harwi-II at Hasylab-Hamburg/Germany (synchrotron) are able for combined strain profile and texture gradient investigations non-destructively. The newly installed robot at STRESS-SPEC allows a very flexible sample manipulation for both types of experiments. First results are presented. Synchrotron radiations with higher brilliance are favoured for small gauge volume and fast measurements. That opens the field of in situ loading (tension-, compression-, cyclic loading) and in situ welding investigations.

Worldwide materials science diffractometers at large scale facilities were built recently to improve experimental options for the characterization of advanced materials. Thermal neutrons as well as hard X-rays have a relatively high penetration power that non-destructive investigations of stress profiles and texture gradients are possible. Due to the main difference between neutrons and photons, which is the brilliance of the beam, the gage volume of synchrotron experiments is much smaller than with neutrons. That means, according to the material itself local resolution in mm-scale is preferred by neutrons and in μm scale by synchrotron radiation. The microstructure of laser welded Al shows fine grained parts were synchrotron radiation can be used while coarse grained parts need neutrons for better grain statistics. Both radiations can also be used to perform in situ experiments for stress and texture analysis. A combination of neutron and synchrotron measurements was used to explain the texture influence on the activation of twinning during Mg-extrusion. Neutron diffractometers, such as Stress-Spec@FRM II/Garching-Germany, or synchrotron diffractometers, such as Harwi-II@Haslab/Hamburg-Germany, are excellent for materials characterization in combination with electron diffraction and laboratory X-ray diffraction.

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.

Mechanical surface treatments such as shot peening (SP) or ball-burnishing (BB) induce plastic deformation close to the surface resulting in work-hardening and compressive residual stresses. It enhances the fatigue performance by retarding or even suppressing micro-crack growth from the surface into the interior. SP and BB were carried out on a solution heat treated (SHT) Ti-2.5Cu. The investigations of compressive and balancing tensile residual stresses need a combination of energy-dispersive synchrotron (ED) and neutron diffraction. Essential for the stress distribution is the stress state before surface treatments which was determined by neutron diffraction. Results show that the maximum compressive stress and its depth play an important role to improve the fatigue performance.

The plastic anisotropy of ultrafine grained aluminium alloys AA1050 and AA6016 produced by accumulative roll bonding (ARB) has been investigated by tensile deformation via the Lankford parameter. The average normal and planar anisotropies slightly increase (from 0.6 to 0.9) and decrease (from 0.6 to −0.7) as a function of ARB cycles, respectively. The global textures measured by neutron diffraction are used to simulate the Lankford and anisotropy parameters of the plates after 0, 2, 4, 6 and 8 ARB cycles with the help of the viscoplastic polycrystal self-consistent model. Simulation results are compared with those from experiment and discussed with regard to texture, strain rate sensitivity, grain shape and slip system activity.

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 a cube-oriented Ni single crystal after one-pass equal channel angular pressing (ECAP) was measured globally and locally by neutron and synchrotron radiation, respectively. The texture is characterized by a TD rotated cube, a split C component and a partial B fiber. These components are heterogeneously distributed in the ECAP billet. Due to friction at the die walls, the rotated cube is mainly observed in the top and bottom parts of the billet, the split C dominates in the central part. The experimental results with respect to component intensity, position from ideal orientation and asymmetry of component splitting are compared with texture simulations taking into account grain fragmentation. Conclusions concerning polycrystal deformation are drawn.

Aluminium with 5N purity were deformed at room temperature by equal channel angular pressing following Route A up to three passes. The microstructure and the crystallographic texture were investigated by orientation imaging microscopy and electron backscatter diffraction, respectively. The microstructure showed complete recrystallization after the first ECAP pass onwards. The grain size decreased slightly with increasing number of passes. The corresponding texture consisted of an oblique cube component. The oblate grains and the cube texture were rotated anticlockwise about the transverse direction. The inclination of grains with respect to the direction of ECAP was dependent on the distance from the top of the billet and changed from pass to pass. The mechanism of formation of the microstructure and texture is discussed in the light of the physical phenomena involved.

Investigations on texture evolution and through-thickness texture heterogeneity during equal channel angular pressing (ECAP) of pure magnesium at 200 degrees C, 150 degrees C and room temperature (RT) was carried out by neutron, high energy synchrotron X-ray and electron back-scatter diffraction. Irrespective of the ECAP temperature, a distinctive basal (B) and pyramidal (C-2) II type of fibers forms. The texture differs in the bottom 1 mm portion, where the B-fiber is shifted similar to 55 degrees due to negative shear attributed to friction. (C) 2015 Elsevier Inc. All rights reserved.