Electron Backscatter Diffraction Method Research Articles

Structural, Microstructural, Elastic, and Microplastic Properties of Aluminum Wires (from AAAC (A50) Cables) after Fatigue Tests

Single Al wires from unused AAAC (A50) cables were studied after laboratory fatigue testing, which simulated processes arising in these wires during their operation in the cables of overhead power lines (OPLs) and are valuable for predicting the lifespan of cables of OPLs. These wires, which were either fractured during testing (maximum loads—149.4–155.9 MPa; number of cycles till rupture—83,656–280,863) or remained intact, were examined by X-ray diffraction, electron backscatter diffraction, densitometry, and acoustic methods. An analysis of the structural, microstructural, and elastic-microplastic properties of the wires revealed common characteristics inherent in the samples after operation in OPLs and after fatigue tests, namely a decrease in the integral and near-surface layer (NSL) densities of the wires, a decrease in their Young’s modulus and microplastic stress, and an increase in the decrement. However, the tests did not fully reproduce the environmental influence, since in contrast to the natural conditions, no aluminum-oxide crystallites were formed in NSLs in tests and the microstructure was different. A comparison of the characteristics of the broken and unbroken wires allows us to suggest that the fastening locations of the wires are crucial for their possible failure.

Analysis of slip transfer behavior of tantalum during quasi in-situ compression

This paper reports a quasi in-situ study on the plastic deformation behavior of high purity tantalum, particularly the slip activation and slip transfer, using the electron backscatter diffraction method. We found that the rotation degree of grains is in the range of 0–15°; the rotation axes of slip-activated grains are mainly concentrated in the three corners, while the axes of slip-transfer ones are concentrated near {111} corner in the stereographic triangle. Microstructural parameters including grain size and grain aspect ratio were found to have no apparent relationships with the slip activation or slip transfer process. Most m' factors for the grains underwent slip-transfer are larger than 0.27, and most slip systems involved in the slip-transfer observations are associated with relatively high Schmid factors (SFs), indicating that slip would more easily transfer through the boundaries with large m' factors. In addition, according to the distribution of geometrical necessary dislocation density and the SF of slipping activated grains, we found the slip transfer process is affected by a combination of factors, including the SF, m' factor, and the strain concentration in local regions.

Low temperature plasticity of microcrystalline Al–Li alloy

The plastic deformation of Al-3.8 at.% Li polycrystals processed by the equal-channel angular hydroextrusion (ECAH) were investigated during tension in the temperature range of 4.2–400 K. The evolution of the microstructure during loading was studied by the electron backscatter diffraction (EBSD) method, including the orientation and kernel average misorientation (KAM) mappings. In as-prepared state the microstructure characterized by grains with small misorientation angles and a high density of dislocations. The deformation of a sample at 120 K leads to increase in the density of deformation defects while at 290 K to their decrease. The strong temperature sensitivity of the yield strength indicates the thermally activated nature of the plastic deformation. An increase in the plasticity and strength of polycrystals with decreasing temperature is explained by a decrease in the dislocation annihilation due to a decrease in the mobility of atoms, resulting in increase in the strain hardening rate. A nonmonotonic dependence of the activation volume Va(T) with a maximum at 180 K was established from stress relaxation data. The analysis of stress-strain curves and microstructure evolution indicate a dominance of thermally activated mechanism of intersection of the forest dislocations below 180 K and an increase in the activity of recovery processes at moderate temperatures.

Особенности микроструктуры и микротекстуры среднеуглеродистой стали, подвергнутой сероводородному растрескиванию под напряжением

Increasing the resistance of steel products to sulfide stress cracking (SSC) is one of the topical issues of the oil and gas industry. Among various factors determining the SSC resistance of a material is the structure-phase state of the material itself and the crystallographic texture associated with it. This paper analyzes these features using the scanning electron microscopy (SEM), transmission electron microscopy (TEM), and microroentgen electron backscattered diffraction (EBSD) techniques. As the research material, a production string (PS) coupling made of medium-carbon steel was selected, which collapsed by the mechanism of hydrogen embrittlement and subsequent SSC. For the first time, by the SEM method, using the location and mutual orientation of cementite (Fe3C) particles, at high magnifications, the authors demonstrated the possibilities of identifying the components of upper bainite, lower bainite, and tempered martensite in steels. The presence of the detected structural components of steel was confirmed by transmission electron microscopy (TEM). Using the EBSD method, the detailed studies of microtexture were conducted to identify the type and nature of the microcrack propagation. It is established that the processes of hydrogen embrittlement and subsequent SSC lead to the formation of {101} <0¯10>, {100} <001>, {122} <2¯10>, {013} <211>, {111} <¯100>, {133} <1 ̅2 ̅1>, {32 ̅6 ̅} <201> grain orientations. It is shown that the strengthening of orientations of {001} <110>, {100} <001>, {112} <111>, and {133} <1 ̅2 ̅1> types worsens the SSC resistance of the material. Using the EBSD analysis method, the influence of coincident site lattice (CSL) grain boundaries on the nature of microcrack propagation is estimated. It is found that the Σ 3 CSL grain boundaries between the {122} <2¯10> and {111} <¯100>, {012} <1 ̅1 ̅0>, {100} <001> plates of the upper bainite inhibit the microcrack development, and the Σ 13b, Σ 29a, and Σ 39a CSL grain boundaries, contribute to the accelerated propagation of microcracks. For comparative analysis, similar studies were carried out in an unbroken (original) coupling before operation.

Characterization of geometrically necessary dislocation evolution during creep of P91 steel using electron backscatter diffraction

In this study, the change of geometrically necessary dislocation (GND) has been investigated during the elevated temperature creep of P91 steel. Firstly, the crept microstructures of P91 steel at 873 K and 165 MPa were characterized by electron backscatter diffraction (EBSD). Then, the resultant GND distributions were analyzed in detail. Meanwhile, the GND density was quantitatively estimated by two methods of kernel average misorientation (KAM) and Nye's dislocation density tensor, respectively. The obtained results indicated that during creep of P91 steel, the values of GND density calculated by the KAM method are highly consistent with those of Nye's dislocation density tensor method. Besides, the GND density increases significantly during the initial creep stage and attains the maximum approximately at the transition from initial creep to steady creep. During the subsequent creep, it gradually decreases. In addition, it suggested that the internal stress predicted by the obtained GND density is consistent with previous experimental data. Accordingly, it further demonstrated that the present characterization of GND evolution offers a convenient tool for the microstructure degradation analysis of P91 steel during creep. • The microstructure of P91 steel during creep has been investigated by EBSD method. • The change of GND density was quantitatively characterized by two methods of KAM and Ney's dislocation density tensor, respectively. • The GND densities obtained by the above methods are highly consistent. • The GND densities vary closely with the creep stage, which mainly results from the interaction between dislocation and precipitates.

EBSD analysis of spark plasma sintered SS316-B4C composite

The Electron Backscatter Diffraction (EBSD) method has been characterized as a potential tool for analysing the microstructural changes that occur during the sintering processes and it possesses the ability to depict misorientation diagrams, pole figures and grain size distribution. The present work focuses on observing the microstructure evolution of the prepared 316 stainless steel with 10 wt% of B4C samples sintered at the temperatures of 800, 900, and 1000 °C using the Spark Plasma Sintering (SPS) method. The samples are in the equiaxed form of recrystallized grains and they are elongated. Further, the samples sintered at 900 °C are equally recrystallized compared to other samples sintered at 800 and 1000 °C, where the microstructure is partially recrystallized with a high fraction. The result is explicable, by increasing the carbon content it causes the reduction of grain boundaries as well as decreases the migration rate of twin boundary generation. Hence, twin character loss is accelerated by the increase of carbon content with low-angle boundaries, and because of the typical drag effect, it has been discovered that the dynamically recrystallized grain size is reduced. The partitioning of these microstructures is done to differentiate the sintered sample and the recrystallized grains, based on the Grain Orientation Spread (GOS) map. The experimental investigation has suggested that the samples sintered at 900 °C has a more favourable microstructure analysis than the other samples sintered at 800 °C and 1000 °C, respectively.

Quasi in-situ observations of microstructure evolution during low cycle fatigue in carbide-free bainitic steel

Microstructure evolution during fatigue is crucial to the initiation and propagation of fatigue cracks in carbide-free bainitic steels. Utilizing quasi in-situ electron back-scattered diffraction method, the morphology of retained austenite and the accumulated plastic deformation within the bainitic laths at different fatigue stages were characterized. The observations disclosed that the retained austenite in various locations has different mechanical stability, and the dislocations in the bainitic laths will evolve to low-energy substructures continually throughout the fatigue process. Furthermore, combined with hysteresis curves analysis, a microstructural evolution model that comprehensively considered the retained austenite stability and the evolution of dislocations was proposed.

Fretting wear behaviour of ultrafine-grained copper produced by cryogenic temperature extrusion machining

Cryogenic temperature extrusion machining (CT-EM), as a new process, was first applied for preparing ultrafine-grained (UFG) copper strips. The microstructure evolution and mechanical properties (hardness and fretting wear) were characterised by electron backscatter diffraction and transmission electron microscopy methods. Refined grains (450 nm) and high dislocation density could be obtained by CT-EM because of effectively suppressing heat generation and the annihilation of dislocations. As a result, the CT-EM sample exhibited enhanced fretting wear properties, e.g. a much lower friction coefficient (reducing 0.1–0.2) and a lower wear loss (decreasing 32–45%) were achieved due to its enhanced hardness and refined microstructure. In-depth, the delamination and oxidation wear proved to be the primary wear mechanism of the CT-EM sample under dry wear conditions.

Crack initiation and short crack propagation of friction stir welded TC17 alloy joint

Heterogeneities of microstructure, tensile and fatigue behavior of FSWed titanium alloy joint were in-situ studied by utilizing replica, DIC and electron back-scattered diffraction methods. Banded TMAZ consisting of needle-like α precipitates and elongated αp within DRXed β grains bridges the HAZ and SZ. Fine β grains in SZ contribute to the highest tensile strength in the 3rd layer. Fatigue cracks prefer to nucleate from HAGBs and {112} 〈111〉 slip deformation of β structure in the 2nd layer of SZ below 210 MPa and 3rd layer of HAZ otherwise. Transgranular crack propagation along the {112} planes exhibits a higher crack growth rate in HAZ than SZ.

Reveal the Viscoplastic Behaviour and Microstructure Evolution of Stainless Steel 316L.

Stainless steel 316L is a widely used structural material in the nuclear industry because of its excellent corrosion resistance and mechanical properties. However, very little research can be found on its viscoplastic behaviour and microstructure evolution at warm and hot deformation conditions, which hinder the possible application of advanced manufacturing technologies for producing complex parts, such as superplastic forming or hydroforming. The aims of this study are to explore stainless steel 316L’s viscoplastic behaviour, to determine its strain rate sensitivities, and to reveal its underlying microstructure evolution; this will allow appropriate manufacturing (forming) technologies and the optimal forming condition to be determined. Hence, isothermal tensile tests at 700 °C, 800 °C, 900 °C, and 1000 °C at strain rates of 0.01 s−1 and 0.001 s−1 have been conducted. Moreover, the corresponding microstructure evolution, including the grain orientation and geometrically necessary dislocation density, has been revealed by the electron backscatter diffraction method. The data show the viscoplastic behaviour of stainless steel 316L under various thermomechanical deformation conditions and how microstructure evolution influences the viscoplastic flow stress.

A study on microstructure development and mechanical properties of pure copper subjected to severe plastic deformation by the ECAP-Conform process

Commercially pure copper rod was successfully subjected to severe plastic deformation by applying the continuous equal channel angular pressing (ECAP-Conform) method at room temperature. Microstructural characterizations of copper rod samples at various stages of plastic deformation were carried out by optical microscopy and electron backscatter diffraction methods. X-ray diffractometry and Kernal average misorientation were used for dislocation density estimations. Microstructural evaluations revealed grain size change of 30 μm for the initial annealed copper rod to less than 5 μm and even 100 nm for severely deformed samples. Mechanical behaviors of samples after different deformation stages were characterized using tensile and hardness tests. The ultimate tensile strength of the severely deformed copper rod was increased threefold by ECAP-Conform while elongation halved in comparison to the initial annealed copper. Low-temperature annealing of severely plastic deformed samples led to bi-modal grain size distribution and lowering of strength accompanied by the increase of elongation. Tensile properties of severely deformed and then annealed copper samples showed around a 40% increase in both ultimate tensile strength and elongation in comparison to the initial annealed copper rod.

Implementation of Exceptional Microstructures and Mechanical Properties of Structural Carbon Steel Tubes by Friction Welding

In this study, friction welding was applied to carbon steel tubes at a high speed condition to achieve an eco-friendly welding process and a superior mechanical performance. Friction welding is a very efficient process for joining materials without defects, especially with joint rods or tubes. For this study, cold drawn carbon steel tubes (AISI 1020) were introduced as the base material and successfully joined by friction welding. Friction welding was performed with parameters of a burn-off length (1, 2 and 5 mm). In order to analyze the welds, the electron backscattering diffraction method was introduced and observed the grain boundary characteristic distributions such as grain size, shape and orientation. To evaluate the relationship between the mechanical properties and microstructure, Vickers microhardness and tensile tests were introduced. As a result, the yield strength of the welds significantly increased relative to the base material at all conditions, and which derived from the microstructure development like a refined acicular ferrite grains through the dynamic recrystallization during the welding. Consequently, we suggest the optimum conditions of the friction welding with the interdependence of the microstructures and mechanical properties in this study. This demonstration substantially offers the possibility of an eco-friendly environment and superior tube welding quality without any defect and harmful gases at the high speed welding process as well as at the lowest cost. This technology can be extended to mass production processes with exceptional benefits for various industries.

Zirconolite Polytypes and Murataite Polysomes in Matrices for the REE-Actinide Fraction of HLW.

Electron backscatter diffraction (EBSD) has been used for more than 30 years for analyzing the structure of minerals and artificial substances. In recent times, EBSD has been widely applied for investigation of irradiated nuclear fuel and matrices for the immobilization of radioactive waste. The combination of EBSD and scanning electron microscopy (SEM/EDS) methods allows researchers to obtain simultaneously data on a specimen’s local composition and structure. The article discusses the abilities of SEM/EDS and EBSD techniques to identify zirconolite polytype modifications and members of the polysomatic murataite–pyrochlore series in polyphase ceramic matrices, with simulations of Pu (Th) and the REE-actinide fraction (Nd) of high-level radioactive waste.

Quasi in-situ study on the slip activation mechanism of high purity tantalum during compress deformation

The microstructure evolution is very complex during the processing of tantalum sputtering target for integrated circuits, and the deformation mechanisms for this evolution is still unclear. This work aims to investigate the deformation mechanism in a quasi-in-situ way, particularly the activation of slip systems, lattice rotation, and strain concentration, utilizing the electron backscatter diffraction (EBSD) method. We found that the maximal orientation density increased after the deformation, especially the content of both the {111}<uvw> and {100}<uvw> components increased while the {110}<uvw> orientations decreased after the deformation. The lattice rotation leads to misorientation between grain orientations before and after the deformation, and the misorientation axes seem to be randomly distributed during the deformation. The rotation behavior can be adequately described by the activation of both {110}<111> and {112}<111> slip systems, which were found to have no linear relationship with grain size or grain aspect ratio, but are related to the Schmid factors and strain concentration situations. In particular, the inhomogeneous geometrical necessary dislocations distribution indicates the complicated situation of flow stress, and the slip systems activated with smaller Schmid factors are associated with the local heterogeneous strain concentrations.

Deuterium permeation behavior in a FeCrAl-based alloy containing Mo, Nb and Ta elements for LWR cladding application

The deuterium permeation behavior of a FeCrAl-based alloy containing Mo, Nb and Ta elements was investigated by gas-phase deuterium permeation testing, transmission electron microscopy, X-ray diffraction and electron backscatter diffraction methods. The results show that the higher the test temperature, the greater the steady-state permeation flux of the FeCrAl-based alloy. As the upstream deuterium pressure increases, the steady-state permeation flux of the FeCrAl-based alloy also increases. The pressure exponent n is between 0.5 and 1, indicating that deuterium permeation in the FeCrAl-based alloy is controlled by a combination of bulk diffusion and surface processes. This phenomenon is caused by the oxide film generated on the surface of the FeCrAl-based alloy during deuterium permeation test. The deuterium permeability of the FeCrAl-based alloy is about 37 times that of 316 L and 95 times that of Zircaloy-4 at the typical operating temperature of 300 °C. At 360 °C, the deuterium permeability of the FeCrAl-based alloy is about 25 times that of 316 L, and about 32 times that of Zircaloy-4. Compared with 316 L and Zircaloy-4 alloy, the activation energy of deuterium permeation of the FeCrAl-based alloy is smaller, indicating that deuterium permeates more easily in the FeCrAl-based alloy. The activation energy of deuterium diffusion in the FeCrAl-based alloy is also smaller, indicating that deuterium diffuses more easily in the FeCrAl-based alloy.

Fine grains within narrow temperature range by tuning strain-induced boundary migration dominated recrystallization for selective laser melted Inconel 718

In this study, fine grains are achieved with weak texture of selective laser melted Inconel 718 (SLM IN718) if annealed within a narrow temperature range (1,070 ∼ 1,090 °C), while abnormal grain growth (AGG) is induced if annealed at temperature higher than that range, resulting in large matrix grains and twins. By a novel quasi-in-situ electron backscatter diffraction (EBSD) method, the recrystallization of SLM IN718 is primarily dominated by strain-induced boundary migration (SIBM) at 1,150 or 1,075 °C via statistical analysis. In particular, AGG at 1,150 °C is attributed to quick consumption of the high-strain regions due to a higher grain boundary (GB) velocity, while fine grains at 1,075 °C attributed to activation of more SIBM grains and uniform growth of these grains due to a slower GB velocity. The techniques proposed in this study can also work well for other SLM face-centered cubic alloys.

Microstructural Characterization of Additively Manufactured Metal Components Using Linear and Nonlinear Ultrasonic Techniques.

Metal additive manufacturing (AM) is an innovative manufacturing technology that uses a high-power laser for the layer-by-layer production of metal components. Despite many achievements in the field of AM, few studies have focused on the nondestructive characterization of microstructures, such as grain size and porosity. In this study, various microstructures of additively manufactured metal components were characterized non-destructively using linear/nonlinear ultrasonic techniques. The contributions of this study are as follows: (1) presenting correlation analyses of various microstructures (grain size and texture, lack of fusion, and porosity) and ultrasonic properties (ultrasonic velocity, attenuation, and nonlinearity parameters), (2) development of nondestructive microstructural characterization techniques for additively manufactured components; and (3) exploring the potential for the online monitoring of AM processes owing to the nondestructive nature of the proposed technique. The performance of the proposed technique was validated using additively manufactured samples under varying laser beam speed conditions. The characteristics of the target microstructures characterized using the proposed technique were consistent with the results obtained using destructive optical microscopy and electron back-scattered diffraction methods.

Lath martensite substructure evolution in low-carbon microalloyed steels

Lath martensite substructures in as-quenched plain carbon steels exhibit dislocation-like contrast in the transmission electron microscope. More recent observations reported internal twins and nanoscale auto-tempered intra-lath carbides as additional lath substructures in ultra-low-C binary Fe–C steels. Modern microalloyed steels often have similar ultra-low C contents besides microalloying elements like Ti, Nb or V and, more recently, Mo, to achieve high strength, toughness and weldability. Nonetheless, little is known about the lath substructure evolution in the as-quenched state of microalloyed steels. This study investigates the hierarchical martensite substructure evolution post-quenching of microalloyed Nb and NbMo steels with 0.1 wt% C. Hierarchical microstructure characterization was done using scanning and transmission electron microscopy, and electron backscatter diffraction methods including parent grain reconstructions with MTEX. Thermokinetic simulations using MatCalc to determine the carbide evolution during auto-tempering were corroborated with site-specific transmission electron microscopy. Mo addition led to lowering of the martensite start temperature, yet the Nb steel showed a finer hierarchical microstructure. Finer laths with in-lath dislocations, short and long twins, and lath boundary decoration of carbides were found in the Nb steel. Conversely, laths in the NbMo were wider, with frequent intra-lath auto-tempered precipitates in the vicinity of dislocations, without twins.

Diffraction methods in the characterization of new mineral species

Data from publications describing new minerals in the periods 2001–2005 and 2016–2020 have been analysed to evaluate the contributions of diffraction methods to the new mineral characterisations. The two periods were chosen to be on either side of a sudden increase in new mineral descriptions from ∼50 to 120 per year and coincidentally correspond to the changeover from the majority (60%) of the new descriptions using photographic film cameras to record the powder diffraction patterns of the minerals, to using modern diffractometers. During both periods, diffraction data obtained using laboratory-based single-crystal diffractometers accounted for almost three-quarters of the crystallographic studies. Modern diffractometers can now routinely be used to collect high-quality data on crystals down to a few μm in size, once the province of synchrotrons. Large facility-based diffraction centres like synchrotrons and scientific nuclear reactors account for less than 10% of the new mineral publications. The review focuses on diffraction methods for the characterisation of fine-grained minerals, with sub-μm sized crystals. Transmission electron microscopy/electron diffraction methods are important for these cases, with an exponential increase in 3D ED methods during the last 15 years and increased usage of electron back-scattered diffraction methods for micro-inclusion minerals, especially in meteorites.

Microstructure and temperature-dependent mechanical behavior of hot-rolled TRIP-assisted microalloyed steel

The effect of deformation temperature (in a temperature range −60 °C–140 °C) on the kinetics of strain-induced martensitic transformation in a hot-rolled multiphase Fe-0.24C-1.5Mn-0.87Si-0.4Al-Nb-Ti steel containing 15% of retained austenite was investigated. A complex microstructural analysis was performed using experimental techniques characterized by different resolutions: the scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The analysis of the tendency of different morphology retained austenite to martensitic transformation was performed. The quantitative analysis of the temperature-dependent stability of γ phase was carried out using the XRD and EBSD methods. The thermodynamic model predicting the changes in the stability of retained austenite at different temperatures was developed based on experimental results. Obtained results showed that both the deformation temperature and morphology of retained austenite affect substantially the stability of retained austenite. • The strategy for designing the stability of retained austenite was developed using experimental and modelling approaches. • The temperature-dependent mechanical behavior of hot-rolled TRIP steel was explained. • The chemical driving force for strain-induced martensitic transformation was determined. • The complex microstructural analysis was applied to link microstructure-properties behavior.