Electron Backscatter Diffraction Method Research Articles

Analysis of the Creep Mechanism of Low-Alloy Steel in Terms of Plastic Deformation

AbstractAs the proportion of renewable energy sources within the energy grid increases, boiler operations increasingly rely on managing disparities in energy supply. This condition substantially curtails their operational lifespan due to frequent switching cycles. Materials exposed to prolonged stress at high temperatures in harsh environments gradually degrade and eventually fail catastrophically. Thus, understanding processes like creep is essential for accurately evaluating the condition of operational components under new operational standards in power plants. In this regard, this paper introduces an innovative methodological framework for analyzing the creep mechanism, focusing on the plastic deformation of a crucial pipeline segment, specifically an elbow composed of 14MoV6-3 steel, both before and after extensive usage periods (164,000 and 302,000 h). The study explored the development of microstrain from the material's surface employing the electron backscattered diffraction method. This analysis assessed how operational durations influence dislocation structural changes, as examined by synchrotron radiation techniques, across a material depth from 0 to 1.5 mm. Based on these observations, the extent of deformation over time was demonstrated. Furthermore, the evolution of precipitation processes was investigated through transmission electron microscopy. These tests allowed to obtain and compare information on the dislocation structure of the tested steel after service in creep conditions, of small and large volumes of material.

Effects of heat input on microstructure evolution and corrosion resistance of underwater laser cladding high-strength low-alloy steel coating

The effects of heat input on the microstructure evolution and corrosion resistance of the high-strength low-alloy (HSLA) steel coating obtained by wire-feed underwater laser cladding were studied. Optical digital microscope, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscope (TEM), electron back-scattered diffraction (EBSD), electrochemical tests, laser microscope and other characterization methods were used. As the heat input increased, the smoothness of the underwater cladding coating improved, with little changes in elemental distribution and phase composition. However, the content of acicular ferrite increased, while the amounts of lath bainite, lath martensite, and granular bainite decreased. As the heat input increased from 0.4 to 0.55 kJ/mm, the grain size increased from 25.3 to 55.9 μm, the proportion of low-angle grain boundaries rose from 61.3 % to 69.1 %, and the texture intensity of the (110) crystal plane increased from 16.22 to 23.83. Meanwhile, the dislocation density decreased from 4.9 × 1014 to 4.1 × 1014 m−2. These changes enhanced the corrosion resistance of underwater coating. As the heat input increased from 0.4 to 0.55 kJ/mm, the corrosion current density decreased from 2.13 × 10−5 to 3.35 × 10−6 A/cm2, and the corrosion potential increased from −0.823 to −0.529 V. Additionally, the depth-to-width ratio of the corrosion pits decreased from 0.255 to 0.053. This study laid the foundation for high-quality in-situ underwater repairs of ships and submarines made of high-strength steel.

Cross-rolling induced texture randomization and structural evolution for improved plastic isotropy in Al-Mg alloys with high Mg content

Plastic anisotropy is a key factor that affects the formability and performance of Al-Mg alloys. In this study, the effects of Mg content and strain path shifting from unidirectional rolling (UDR) to cross rolling processes (CR) on plastic anisotropy in Al-Mg alloys were investigated. Al-6 and 9Mg alloys were heat-treated and rolled in two different ways: the first was a UDR process, and the other was a CR process at room temperature. The rolled specimens were analyzed by electron backscattered diffraction method and tensile test. High Mg content suppresses the formation of texture that strengthens the plastic anisotropy in both UDR and CR processes. CR significantly reduces the rolling texture area fraction, leading to greater texture randomness compared to UDR. CR promotes the formation of low-angle deformation bands, which low-angle bands appear to have a weaker impact on deformation resistance and may contribute to the reduced anisotropy in CR-processed materials. CR results in a more uniform distribution of stored energy. R-value which represents plastic anisotropy decreases by shifting from UDR to CR, and by increment of Mg content. Overall, this study demonstrates that CR is a promising approach for improving the formability and performance of Al-Mg alloys by effectively controlling plastic anisotropy.

Mapping of Microscopic and Local Stress-Strain Curve Information by Combination of Digital Image Correlation and High-Resolution Electron Backscatter Diffraction Methods

Mapping of Microscopic and Local Stress-Strain Curve Information by Combination of Digital Image Correlation and High-Resolution Electron Backscatter Diffraction Methods

Study on low fatigue damage behavior of TC17 titanium alloy with basket-weave microstructure

Room-temperature low-fatigue tests were conducted on TC17 titanium alloy, and the low-fatigue damage behavior of TC17 titanium alloy with a basket-weave microstructure at room temperature was investigated. The results show that TC17 titanium alloy exhibits different cyclic hardening/softening phenomena at different strain amplitude (εta) levels, which was closely related to the magnitude of strain amplitude, the crack sources of all specimens generated on the surface, and the number of crack sources increases with the increase of strain amplitude level. The competitive relationship between back stress hardening and frictional stress softening caused by changes in different microstructures is the reason for the occurrence of different cyclic hardening/softening phenomena. The relationship between the holes and secondary cracks near the fracture surface and the basket-weave microstructure was further discussed. The secondary cracks/holes were more likely to initiate in the primary α phase where the solid solution strengthening effect was weak. In addition, the interaction between the secondary crack propagation path and the nearby α lamellae was studied by the Electron Backscatter Diffraction (EBSD) method.

A Study of the Internal Deformation Fields and the Related Microstructure Evolution during Thermal Fatigue Tests of a Single-Crystal Ni-Base Superalloy.

Ni-base superalloys operate in harsh service conditions where cyclic heating and cooling introduce deformation fields that need to be investigated in detail. We used the high-angular-resolution electron backscatter diffraction method to study the evolution of internal stress fields and dislocation density distributions in carbides, dendrites, and notch tips. The results indicate that the stress concentrations decay exponentially away from the notch, and this pattern of distribution was modified by the growth of cracks and the emission of dislocations from the crack tip. Crack initiation follows crystallographic traces and is weakly correlated with carbides and dendrites. Thermal cycles introduce local plasticity around carbides, the dendrite boundary, and cracks. The dislocations lead to higher local stored energy than the critical value that is often cited to induce recrystallization. No large-scale onset of recrystallization was detected, possibly due to the mild temperature (800 °C); however, numerous recrystallized grains were detected in carbides after 50 and 80 cycles. The results call for a detailed investigation of the microstructure-related, thermally assisted recrystallization phenomenon and may assist in the microstructure control and cooling channel design of turbine blades.

Thermal restoration kinetics and microstructural evolution of an Mg-RE alloy during annealing by quasi-in-situ observation

Quasi-in-situ electron backscatter diffraction method is applied to properly investigate thermal restoration kinetics and microstructural evolution of a commercial WE54 alloy after 10 % engineering pre-strain and post-annealing at 500 °C for 10, 35, and 70 min. Results show a reduction in the average grain orientation spread can effectively evaluate the restoration kinetics compared to other characteristics like average grain size or average misorientation angle. For microstructural evolution, nucleation behavior and abnormal grain growth of recrystallization nuclei as well as evolution of deformation twin have been investigated in detail. Low-angle grain boundary network due to the recovery effect provides recrystallization nuclei in the early stage of annealing, after which both continuous and discontinuous recrystallization nuclei are observed near deformation twin boundaries and original high-angle grain boundaries. Afterwards, grains with a tilting angle of 30° from the transverse direction grow abnormally, replacing the deformed grains, deformation twins, and part of some recrystallized grains. In addition, some twins can grow into the adjacent grains while de-twinning also occurs depending on twin orientations during thermal restoration.

Isothermal and thermomechanical fatigue crack growth behavior of 316LN stainless steel under load‐ and strain‐controlled modes

AbstractCrack growth tests of 316LN stainless steel under load‐controlled and strain‐controlled thermo‐mechanical fatigue (TMF) loadings at the temperature range of 350°C ~ 550°C were conducted. Moreover, the isothermal fatigue (IF) crack growth tests at the maximum temperature of 550°C were performed for comparison. The differences in IF and TMF crack propagation behavior under different loading conditions were thoroughly discussed, and the underlying mechanisms were revealed by a comprehensive characterization of the deformation state of the crack tip region using digital image correlation (DIC) and electron backscatter diffraction (EBSD) methods. Furthermore, it was found that the EBSD characterization was simply based on a single plane made it difficult to evaluate the complex crack growth behavior. In addition, the limitations of the classical parameter of stress intensity factor under TMF loading were presented.

Quasi-in-situ observing unusual grain orientation rotation during the process of static recrystallization grain growth in Mg–Zn-Gd alloy

The orientation (including the c axis orientation and crystal direction parallel to rolling direction) evolution of grown recrystallization grains during annealing at 250 °C for 45–180 min in Mg–Zn-Gd alloy was characterized by quasi-in-situ electron backscatter diffraction method. An unusual grain orientation rotation during the process of static recrystallization grain growth, rather than common plastic deformation or recrystallization nucleation process, was observed. Due to the higher storage energy, the growth size in the early stage of annealing (1.41 μm) is larger than that in the late stage of annealing (0.73 μm) for most (∼76%) grains, and corresponding average c-axis rotation angles are 3.65° and 1.39°, respectively, indicating that the larger the increase in grain size, the greater the changing degree in grain orientation. It is speculated that the orientation rotation during grain growth process is mediated by the interaction between dislocations and grain boundaries. The results reported in the current paper can provide a new insight into the study on the relationship between preferential grain growth and non-basal texture formation in rare earth contained Mg alloys.

Unexpected texture transition induced by grain growth during static annealing of a dilute Mg-1Al alloy

Conventional rolled Mg-Al alloy sheets typically exhibit strong basal textures that remain and may even strengthen after recrystallization annealing due to the preferential growth of basal-oriented grains, resulting in poor formability at room temperature. Therefore, the knowledge of recrystallization and grain growth is critical for modifying textures of Mg-Al alloy sheets. The static recrystallization and texture evolution in a cold-rolled dilute Mg-1Al (wt.%) alloy during various annealed temperatures ranging from 300 °C to 450 °C, have been investigated using the quasi in-situ electron backscatter diffraction (EBSD) method. The as-rolled Mg-1Al alloy shows a dominant basal texture, which weakens and broadens in the rolling direction (RD) during the subsequent annealing, accompanied by the formation of 〈101¯0〉 texture component. Particularly, the 〈101¯0〉 texture component is more pronounced after annealing at high temperatures. The quasi in-situ EBSD results show that recrystallized grains are mainly induced by shear bands, which exhibit a wide spectrum of orientations with c-axis tilt angles ranging 20°-45° from the normal direction (ND). Orientations of shear band-induced recrystallized grains are retained during the entire recrystallization process, resulting in a reduction in the texture intensity. Moreover, recrystallized grains belonging to the 〈101¯0〉 texture component grow preferentially compared to those with other orientations, which is attributed to low energy grain boundaries, especially grain boundaries with ∼30° misorientation angles. Furthermore, the high temperature annealing facilitates the rapid growth of grain boundaries having a 30° misorientation angle, leading to the occurrence of distinct 〈101¯0〉 texture after annealing at 450 °C for 1 h. The results provide insights for texture modification of rare earth-free low-alloyed Mg alloys by controlling annealing parameters.

Effect of Enhanced Grain Refinement in Friction Welded SUS316L Alloy

To investigate the solid state weldability on SUS316L alloy, this work was carried out. Friction welding as a solid state welding was introduced and conducted at a rotation speed of 2,000 rpm and a friction pressure of 25 MPa on tube typed specimens. After this work, the grain boundary characteristic distributions such a grain size, shape and misorientation angle of the welds were clarified by electron backscattering diffraction method. The application of friction welding on SUS316L resulted in a significant refinement of the grain size in the weld zone (6.03 μm) compared to that of the base material (57.55 μm). Despite the grain refinement, the mechanical properties of the welds indicate relatively low or similar to the base material. These mechanical properties are due to dislocation density in the initial material and grain refinement in the welds.

Текстура рекристалізації та анізотропії пружних властивостей листів сталі DC04

We studied steel sheets DC04 (0.06% C, up to 0.35% Mn, up to 0.40% Si, ~ 0.025% S and P) with a thickness of 0.95 mm as delivered. Sheets of A4 size were annealed in a laboratory oven (6000C in an argon atmosphere, hold for 1 hour). The structure of DC04 steel sheets after recrystallization annealing was studied. The microstructure of the steel sheets under study is presented from the side of the rolling plane and in the section of the sheet perpendicular to the direction. In the plane of the sheets, the grains are elongated; in the cross section, the grains are approximately equiaxed. Pole figures (PF) were constructed based on the results of electron backscatter diffraction (EBSD) on a LEO 1455 VP electron microscope at an accelerating voltage of 20 kV from the plane of the sheets and from the section of the sheet perpendicular to the rolling direction. To improve statistics, PF were constructed by averaging reflex stereographic projections from 20 different representative volumes of material relative to the rolling direction and transverse direction. The texture and anisotropy of Young's modulus in the plane and cross section of steel sheets DC04 after recrystallization annealing was studied using EBSD method. A connection has been obtained between ideal orientations that describe the texture in two mutually perpendicular planes and the corresponding integral characteristics of texture (ICT). Rectangular samples with a length of 100 and a width of 10 mm at different angles to the rolling direction every 150 to measure Young's modulus. Samples were processed in a bag to ensure uniform dimensions. Young's modulus was determined by the dynamic method from the frequency of natural transverse vibrations. Three batches of samples were used to construct Young's modulus anisotropy curves. The anisotropy of the Young's modulus in the plane of steel sheets, calculated from the ICT based on the results of EBSD data, is in good agreement with the results of direct measurements. The value of Young's modulus in the direction normal to the plane of the sheet and in the section plane in the direction normal to the plane of the sheet, calculated from the ICT and the values of the compliance constants of iron, coincide. Keywords: texture, pole figure, anisotropy, integral characteristics of texture, Young's modulus.

Degradation of the Cr2O3 layer protectiveness caused by grain refinement during high-temperature oxidation of Cr coatings

To enhance the understanding of the failure mechanism of Cr coatings under simulated loss of coolant accident (LOCA) conditions in pressurized water reactors, an investigation into the isothermal oxidation behavior of Cr coatings in 1200 °C steam was conducted. The structure evolution of Cr coatings was characterized by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) methods. The obtained results reveal the formation of a three-layer structure during the 1200 °C steam oxidation process. This structure comprises a Cr2O3 layer, a residual Cr layer, and a ZrCr2 layer. Over time, the grains in the Cr2O3 layer undergo refinement, leading to an increase in grain boundaries. This phenomenon promotes the inward diffusion of oxidizing medium, contributing to understanding of the degradation of Cr2O3 layer protectiveness after prolonged oxidation. These findings offer valuable insights into the failure mechanism of Cr coatings in high-temperature steam environments.

Study of temperature effect on hydrogen embrittlement in X70 pipeline steel

The study investigates the temperature effect on hydrogen embrittlement (HE) in X70 steel using Devanathan-Stachurski and tensile tests under varying cathodic hydrogen-charging currents. The most severe HE temperature threshold is identified via scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) methods. The temperature thresholds for 10 mA/cm2 and 20 mA/cm2 are 293 K and 283 K, respectively, while no critical temperature at 30 mA/cm2. The underlying mechanism is studied, and a predictive model is established. Also, the primary hydrogen-induced fracture plane is identified as {110}, beneath where hydrogen enhances plastic deformation in {110}<111> and inhibits in {112}<111>.

Coupled Microstructural EBSD and LA-ICP-MS Trace Element Mapping of Pyrite Constrains the Deformation History of Breccia-Hosted IOCG Ore Systems

Electron backscatter diffraction (EBSD) methods are used to investigate the presence of microstructures in pyrite from the giant breccia-hosted Olympic Dam iron–oxide copper gold (IOCG) deposit, South Australia. Results include the first evidence for ductile deformation in pyrite from a brecciated deposit. Two stages of ductile behavior are observed, although extensive replacement and recrystallization driven by coupled dissolution–reprecipitation reaction have prevented widespread preservation of the earlier event. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) element maps of pyrite confirm that many pyrite grains display compositional zoning with respect to As, Co, and Ni, but that the zoning is often irregular, patchy, or otherwise disrupted and are readily correlated with observed microstructures. The formation of ductile microstructures in pyrite requires temperatures above ~260 °C, which could potentially be related to heat from radioactive decay and fault displacements during tectonothermal events. Coupling EBSD methods with LA-ICP-MS element mapping allows a comprehensive characterization of pyrite textures and microstructures that are otherwise invisible to conventional reflected light or BSE imaging. Beyond providing new insights into ore genesis and superimposed events, the two techniques enable a detailed understanding of the grain-scale distribution of minor elements. Such information is pivotal for efforts intended to develop new ways to recover value components (precious and critical metals), as well as remove deleterious components of the ore using low-energy, low-waste ore processing methods.

Mechanical-metallurgical-corrosion behavior of Cr-Si-S-C ferritic/ferromagnetic stainless steel, known as AISI 430F, before and after isothermal recrystallization annealing

The research investigates the mechanical and corrosion behavior of Cr-Si-S-C ferritic stainless steel (FSS), known as EN1.4105, which is equivalent to AISI430F. The static isothermal recrystallization annealing is applied to the cold-drawn (CD) materials with two different reduction rates (RRs) of 20 and 35%, under various conditions of soaking temperature and incubation time, which provide 42 unique specimens. The microstructures of CD and annealed materials are characterized by using the electron backscatter diffraction method. X-Ray diffraction analysis alongside scanning electron microscopy linked with energy-dispersive X-ray spectroscopy are also employed to scrutinize the precipitation of any secondary phases, morphologies, and the related chemical compositions. Two different corrosive chlorinated and acidic electrolyte solutions are used for the potentiostatic-based corrosion tests to investigate the passivation kinetics. The results show that the higher RR, which provides faster recrystallization, results in a higher scale of non-hardenable materials. In addition, the effects of RR and annealing conditions are found to have an impact on the corrosion resistance. Moreover, the material exhibits varied behavior in terms of both passivation layer formation as the immersion in the sulfuric acid electrolyte solution (SAES) and active electrochemical behavior immersing in sodium chloride electrolyte solution (SCES). However, this material shows lower corrosion current density and higher corrosion potential in the SCES compared to the SAES medium. The comprehensive findings underscore the intricate relationship between reduction rates, annealing conditions, microstructural evolution, and corrosion behavior in this FSS. The observed trends provide valuable insights for optimizing material performance and corrosion resistance in practical applications.Graphical abstract

Effects of grain size and temperature on slip and twinning activity in a magnesium-rare earth alloy

Understanding the deformation mechanisms in magnesium alloys is critical to develop the next-generation high-performance magnesium alloys. In this work, the effects of grain size and temperature on slip and twinning activities in WE43 magnesium-rare earth alloy were investigated with the quasi-in-situ electron backscattering diffraction method and slip trace analysis. Compression tests were conducted for the samples with three different grain sizes at room temperature (RT) and liquid nitrogen temperature (LNT), respectively. More pyramidal slips were activated in the fine-grained sample to accommodate the plastic strain instead of more twins generated in the coarse-grained sample, which contributed to its higher strain to failure and strain hardening rate. Numerous individual twins with thin structures formed in the fine-grained sample, while thick twins were observed in the coarse-grained sample. The numerous thin twins and high activities of pyramidal slips in the fine-grained sample would be attributed to the high kernel average misorientation (KAM) value and local stress concentration around grain boundaries. Regarding temperature effects, more thin twins and twin-twin interactions were observed at LNT than at RT, and the KAM value was high around these twin boundaries, which contributed to enhancing the flow stress but reducing the strain to failure at LNT.

Microstructure evolution and deformation mechanism with comparison of Ta-2.5 W and Cu under detonation load

The comparison of microstructure evolution of Cu and Ta-2.5 W liner during explosively formed projectile (EFP) formation was studied. The electron backscatter diffraction method (EBSD) was used to statistically characterize the microstructure of the liner before and after deformation. Both recycled EFPs show strong fiber texture and different degrees of recrystallization. The center of the recycled Cu EFP has strong <001> and <111> preferred orientations along the EFP axis, and the density of the texture changes with the deformation strain. Cu EFP has extensive dynamic recrystallization, up to 88%, which is considered to be a traditional dynamic recrystallization mechanism, the temperature is the main controlling factor in the refinement process. On the contrary, the recycled Ta-2.5 W EFP has a strong <101> fiber preferred orientation, and almost no dynamic recrystallization occurs, large strain deformation is the main factor for the microstructure fragment.

Investigation of fine-scale dislocation distributions at complex geometrical structures by using HR-EBSD and a comparison with conventional EBSD

Dislocation distribution is one of the elementary factors that directly influence deformation processes in structural components. Electron backscatter diffraction (EBSD) analysis is one of the experimental techniques that allow for a semi-quantitative evaluation of the Geometrically Necessary Dislocation (GND) distribution in polycrystals. Owing to its noise floor the accuracy of conventional Hough transformed-based GND analysis is restricted to relatively large plastic strains. This problem can be overcome by using the cross-correlation-based high angular resolution electron backscatter diffraction (HR-EBSD) method. The present study demonstrates the improvements in characterizing localized dislocation distribution using the HR-EBSD method compared to the conventional approach. To demonstrate the efficacy, we investigated two more extreme examples of deformation conditions in polycrystalline zirconium (Zr), 1) a plastically deformed crack tip in presence of applied strain, and 2) a misfit plastic field around a hydride precipitate. The edge, screw and total GND components are compared for both cracked and hydride specimens. Dissimilarities in the identification of screw dislocations and subtle features with misorientation uncertainties are reported using HR-EBSD and conventional EBSD. A direct correlation between slip bands and the HR-EBSD estimated GNDs is presented, enhancing the scope of this approach to identify individual slip bands, which is traditionally challenging for any misorientation-based characterization technique.

Microstructural aspects of fatigue strength of welded joints of medium carbon steels produced by rotary friction welding

The paper studies the resistance to fatigue failure of welded joints of steels 32Mn2-40CrNi2Mo, intended for the production of drill pipes for geological exploration. The connection of pipe billets for the purpose of manufacturing experimental samples was carried out by means of rotational friction welding at various process parameters. The assessment of resistance to fatigue loads was carried out on solid cylindrical samples with a welded joint under conditions of bending with rotation, which made it possible to identify the weakest zone in which the initiation and development of a fatigue crack occurred. The microstructure was studied using optical and electron scanning microscopy using the electron backscatter diffraction (EBSD) method. In the course of research, it was found that the greatest resistance to fatigue loads is provided due to the intensive development of strain hardening processes in the thermomechanical affected zone of welded joints, which depend on the parameters of rotary friction welding.