Electron Backscatter Diffraction Results Research Articles

Microstructure and magnetic properties of SmCo5 sintered magnets

SmCo5 sintered magnets with good thermal stability are mainly used in high-temperature field. In this study, two types of SmCoz powders with different nominal z values were mixed and synthesized into SmCo5 magnets by the traditional powder metallurgy method. The magnetic properties of the SmCo5 sintered magnet are maximum energy product of (BH)max = 172.29 kJ·m−3, remanence of Br = 7.47 × 105 A·m−1 and coercivity of Hci = 2.42 T. The results show that there are three coexisting phases in the magnet, which are SmCo5 phase, Sm2Co7 phase and Sm2O3 phase. The microstructural observation indicates that the average grain size in the magnet is about 8 μm, and the high coercivity of this magnet is attributed to these fine grains. X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) results indicate that the magnet has a well-aligned (00l) orientation texture.

Investigation of Ferroelectric Grain Sizes and Orientations in Pt/CaxSr1⁻xBi₂Ta₂O₉/Hf⁻Al⁻O/Si High Performance Ferroelectric-Gate Field-Effect-Transistors.

Electron backscatter diffraction (EBSD) was applied to investigate the grain size and orientation of polycrystalline CaxSr1–xBi2Ta2O9 (CxS1–xBT) films in ferroelectric-gate field-effect transistors (FeFETs). The CxS1–xBT FeFETs with x = 0, 0.1, 0.2, 0.5, and 1 were characterized by the EBSD inverse pole figure map. The maps of x = 0, 0.1, and 0.2 showed more uniform and smaller grains with more inclusion of the a-axis component along the film normal than the maps of x = 0.5 and 1. Since spontaneous polarization of CxS1–xBT is expected to exist along the a-axis, inclusion of the film normal a-axis component is necessary to obtain polarization versus electric field (P–E) hysteresis curves of the CxS1–xBT when the E is applied across the film. Since memory windows of FeFETs originate from P–E hysteresis curves, the EBSD results were consistent with the electrical performance of the FeFETs, where the FeFETs with x = 0, 0.1, and 0.2 had wider memory windows than those with x = 0.5 and 1. The influence of annealing temperature for C0.1S0.9BT poly-crystallization was also investigated using the EBSD method.

Strain-rate-dependent deformation behaviour of high-carbon steel in compression: mechanical and structural characterisation

Dual-phase high-carbon steels are of significant interest in mining industries particularly in comminution and rock handling applications where the strain rate varies from very low to very high. The effect of quasi-static strain rate on the deformation behaviour of austenite–martensite high-carbon low-alloy steel is investigated for compression loading in this paper. Experiments were conducted at different compressive strain rates (2.56 × 10−4 to 2.56 × 10−1 s−1), and the subsequent microstructural evolution was characterised by optical microscopy, X-ray diffraction (XRD), scanning electron microscopy and electron backscatter diffraction (EBSD) techniques to establish the structure–property correlation. The experimental results indicated an increase in the yield strength (σy) with the increase in the strain rate due to the rate-dependent dislocation velocities. The strain hardening rate of the material exhibited a decreasing trend with an increase in the true strain values for all the applied strain rates. XRD results indicated the phenomenon of deformation-induced martensitic transformation (DIMT) to be rate dependent, whereas EBSD results showed an increase in the Kernel average misorientation values with increase in the strain rate. The volume fraction of retained austenite was observed to be decreasing with an increase in the engineering strain values irrespective of the applied strain rate. The microscopic features of the fracture surfaces showed the presence of transgranular cracking at low strain rates, whereas predominant intergranular cracks were found at higher strain rates. TEM results indicated the decrease in the lath martensites with increase in the strain rate.

New insights from crystallography into the effect of refining prior austenite grain size on transformation phenomenon and consequent mechanical properties of ultra-high strength low alloy steel

Based on new insights from crystallography, this study aims to establish the relationship between prior austenite grain size and mechanical properties and enhance our understanding of Hall-Petch relationship. The refinement of prior austenite grains was achieved by decreasing the austenitizing temperature (from 920 ℃ to 880 ℃) and quenching. In addition, samples subjected to 880 ℃ heat treatment and quenching produced a significantly higher percentage of martensite. Electron backscattered diffraction (EBSD) used to characterize the crystallographic characteristics indicated that the steel subjected to 920 ℃ heat treatment and quenched had larger prior austenite grains, belonging to the transformation of Bain group. After 880 ℃ heat treatment and quenching, the prior austenite grains were smaller and more uniform, which belonged to the transformation dominated by CP (close-packed plane) group. The transformation from Bain group to CP group was related to transformation driving force, and resulted in increase in the density of high angle grain boundaries (DHAGBs). Using thermal expansion approach to measure the initial martensite transformation temperature (Ms temperature), the samples heat treated and quenched at 920 ℃ and 880 ℃ showed Ms temperature of 400 ℃ and 427 ℃, respectively, implying that the phase transformation driving force was increased by refining the prior austenite grain. Charpy impact energy test at −40 ℃ suggested that after 880 ℃ heat treatment and quenching, the Charpy energy increased from 46 J to 92 J, consistent with the results of EBSD.

Optimization of Hot Workability and Control of Microstructure in 18Ni (M250 Grade) Maraging Steel Using Processing Maps

This article examines the hot working characteristics of M250 grade maraging steel by performing isothermal compression tests varying the temperatures and strain rates. A processing map has been developed, indicating microstructurally “stable” and “unstable” regions during hot working. At strain rates (ϵ, ˙, , , , , ) above 0.1 s−1 and temperatures (T) below 1,000°C, stress–strain curves show strain hardening behavior, whereas steady-state behavior is shown at strain rates below 0.01 s−1 and temperatures above 1,050°C. Above 1,150°C, flow softening is observed at 0.001 and 0.01 s−1. In the processing map, two distinct microstructurally stable domains are observed: one is at T = 1,150–1,200°C and ϵ, ˙, , , , , = 0.001–0.01 s−1, and another is at T = 1,000–1,150°C and ϵ, ˙, , , , , = 0.001–0.1 s−1. Based on microstructural observations, electron backscattered diffraction results, and the high efficiency of power dissipation, dynamic recrystallization is the softening mechanism. A constitutive relation useful in computer modeling is developed, using the generated flow stress data.

Microstructure and mechanical performance tailoring of Ti-13Nb-13Zr alloy fabricated by selective laser melting after post heat treatment

The poor ductility of the selective laser melting (SLM)-fabricated parts may lead to the limitation of its applications. Therefore, in the present work, four types of post heat treatments of SLM-proceeded Ti-13Nb-13Zr were performed to tailor the microstructure and mechanical performances. In the super-transus heat treatment, the morphologies of grains are transformed from columnar to equiaxed because of the strain-induced grain boundary migration mechanism (SIBM), while in the sub-transus process, the columnar β grains are remained. In the water quenching process, high resolution transmission electron microscopy analysis revealed that the collapse of the partial layers in the (110) planes and [111] direction results in the original stacking sequence from …ABCABC… to a new stacking sequence …AB’AB’… and an w structure is formed, resulting in the highest ultimate (1155 ± 30 MPa), yield strength (874 ± 30 MPa) and unfortunately the lowest ductility (2.3 ± 0.2%). In the air cooling process, as the heat temperature declines from 750 °C to 650 °C, the electron back-scattered diffraction results show that the coarse and irregular α grains with strong {0001} and {211¯0} orientations are gradually transformed into fine acicular α crystals with the dominated {0001} orientation. In this condition, the residual stresses were released and the fine microstructure was largely retained, thus the high yield strength is maintained (799 ± 10 MPa) and the ductility is improved (7.2 ± 0.3%).

High-Temperature Deformation Behavior of Ti-6Al-2Sn-4Zr-2Mo Alloy with Lamellar Microstructure Under Plane-Strain Compression

High-temperature plane-strain compression of a Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy with a lamellar structure was applied by a thermal simulation machine Gleeble 3800 at a temperature of 1223-1370 K and a strain rate of 0.01-10 s−1. Constitutive relations between the flow stress and strain at different temperatures and strain rates were constructed based on the Arrhenius equation. Processing maps based on the dynamic material model at strains of 0.5, 1.0, and 1.25 were also constructed to analyze the mechanism and instability of high-temperature deformation. Dynamic recrystallization was found to occur at 1223-1313 K and 0.01-0.1 s−1, with a peak efficiency of power dissipation of 70%. Observations of the microstructure demonstrated that α platelets and dynamic globularization were responsible for dynamic softening in the α + β phase field. Flow instability behaviors occurred at 1263-1343 K/1.78-10 s−1, 1233-1283 K/0.1-3.16 s−1, and 1353-1373 K/0.56-1.78 s−1, and adiabatic shear bands and microcracks were observed in these domains. Thus, for the lamellar Ti-6242 alloy, the recommended hot rolling parameters were 1243-1333 K and 0.01-0.1 s−1. Electron backscattered diffraction results revealed that the dynamic restoration mechanism in the β phase field was dynamic recovery when the strain rate was as high as 10 s−1.

Crystal orientation relationships in ternary eutectic [formula omitted]-[formula omitted]-[formula omitted

The microstructure of ternary eutectic Al-Al2Cu-Ag2Al arranges in several patterns of three solid phases during directional solidification. One key question for understanding the behavior of this system is if and how the patterns depend on crystal orientation relationships (ORs) between the solid phases. In order to study the correlation between the ORs and the evolving patterns for different process conditions, electron backscatter diffraction (EBSD) is performed on samples of directionally solidified ternary eutectic Al-Al2Cu-Ag2Al which have been processed with different solidification velocities and temperature gradients. The results show that characteristic ORs occur, influencing the type of the evolving pattern, the alignment of the phases and the degree of order. For one specific OR the pattern was observed to change in response to an imposed increase in the growth velocity even though the OR was retained. Based on the obtained EBSD results, an explanation for the observed behavior is proposed. For the other ORs, specific microstructures were observed for each of them. The outcomes demonstrate that knowledge about crystal ORs is essential to improve the understanding of the pattern formation in complex eutectic alloys.

Effect of grain boundary characteristic on intergranular corrosion and mechanical properties of severely sheared Al-Zn-Mg-Cu alloy

Three kinds of heat treatment procedure, namely solid solution treatment (SST), homogenization heat treatment (HHT) and aging heat treatment (AHT), were adopted to control grain boundary characteristics of Al-Zn-Mg-Cu aluminum alloy after severe plastic deformation. And the experimental researches were employed to find the effect of grain boundary characteristic on intergranular corrosion of severely deformed aluminum alloy, including the optical microscope (OM), transmission electron microscope (TEM), X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD). OM and EBSD observations show that heat treatment for severely sheared Al-Zn-Mg-Cu alloy can significantly increase the fraction of large angle grain boundaries and recrystallized grain boundaries. TEM observations agree well with the results of OM, EBSD and XRD, through the dislocations, the morphology and size of precipitated phase, and the grain boundary style. The results of microhardness and tensile tests maintain that AHT is the best way to improve both strength and plasticity. Intergranular corrosion observations show that sample after HHT has the optimum corrosion resistance while the sample after AHT possesses the worst performance. The influence mechanism of grain boundary characteristic on the corrosion resistance and mechanical properties is investigated in consideration of grain boundary type and precipitates in grain and grain boundaries.

Interpretation of hydrogen-assisted fatigue crack propagation in BCC iron based on dislocation structure evolution around the crack wake

A new model for hydrogen-assisted fatigue crack growth (HAFCG) in BCC iron under a gaseous hydrogen environment has been established based on various methods of observation, i.e., electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM), to elucidate the precise mechanism of HAFCG. The FCG in gaseous hydrogen showed two distinguishing regimes corresponding to the unaccelerated regime at a relatively low stress intensity factor range, ΔK, and the accelerated regime at a relatively high ΔK. The fracture surface in the unaccelerated regime was covered by ductile transgranular and intergranular features, while mainly quasi-cleavage features were observed in the accelerated regime. The EBSD and ECCI results demonstrated considerably lower amounts of plastic deformation, i.e., less plasticity, around the crack path in the accelerated regime. The TEM results confirmed that the dislocation structure immediately beneath the crack in the accelerated regime showed significantly lower development and that the fracture surface in the quasi-cleavage regions was parallel to the {100} plane. These observations suggest that the HAFCG in pure iron may be attributed to “less plasticity” rather than “localized plasticity” around the crack tip.

Effect of alloying elements on room temperature stretch formability in Mg alloys

The effect of alloying elements on room temperature stretch formability and its deformation mechanism was investigated using pure magnesium and its binary alloys containing an element of Ag, Al, Ca, Li, Mn, Pb, Sn, Y and Zn, respectively. All of the alloys as well as pure magnesium were produced by extrusion and had a similar average grain size. The alloying elements clearly affected stretch formability as measured by Erichsen testing. The addition of manganese or yttrium element played a role in improving formability; on the other hand, most of the alloying elements did not improve formability, as exhibited by their limited dome height values, which were similar to or lower than that of pure magnesium. This resulted from their differences in deformation mode. An intragranular misorientation axis analysis using electron back-scatter diffraction results revealed that the Mg-Y alloy had a high fraction of grains amenable to non-basal dislocation slips, which is a helpful deformation mode for improving formability. In contrast, pure magnesium and the Mg-Mn alloy, which had a high limited dome height, did not have a high fraction of such grains. Grain boundary sliding compensated for the lack of <c>-component, such as activating non-basal dislocation slips.

The challenge of acquiring a satisfactory EBSD result of CWSR Zircaloy-4 cladding tube.

We present a methodology combining multiple microscopic methods to analyse a recrystallised Zircaloy-4 sheet and cold-worked stress-relieved (CWSR) Zircaloy-4 cladding, important alloys of structural materials widely used in nuclear application, and emphasis on the challenge of acquiring a satisfactory electron backscatter diffraction (EBSD) result of CWSR Zircaloy-4 cladding material in great details. EBSD is a powerful technique to characterise the crystallographic distribution and lattice type of conductive crystalline materials, especially for a highly textured material like CWSR Zircaloy-4 alloy. However, zirconium alloys are known to be one of the most difficult materials to prepare for EBSD characterisation. We point out that the configuration of the microstructure of the specimen cause the challenge in the EBSD sample preparations. Moreover, the occurrence of tiny zirconium hydride precipitates in Zircaloy-4 increases the difficulty. We believe that the information of the EBSD sample preparation related results in this paper can provide researchers and scientists in this community a useful reference to speed up the EBSD sample preparation of CWSR Zircaloy-4 cladding material and to expect the corresponding EBSD results.

The effect of through thickness texture variation on the anisotropic mechanical response of an extruded Al-Mn-Fe-Si alloy

There is currently a significant scientific and industrial interest in developing material models for the simulation of plastic deformation of aluminum extrusions relevant to their forming and their response during in service events such as vehicle crash. The objective of this work is to evaluate the effect of through thickness crystallographic texture gradients on material mechanical behaviour. This has been studied using a combination of experiments (i.e. pilot scale extrusions and stress-strain curves with the R-value to characterize plastic anisotropy for different loading directions) and the visco-plastic self-consistent (VPSC) polycrystal plasticity simulations on a model alloy system. Two limiting conditions were examined, i.e. unrecrystallized and fully recrystallized conditions. The results of electron backscatter diffraction (EBSD) characterization show that there is a significant through thickness variation in texture for both cases. However, the implications of the texture gradient on the macroscopic plastic response were relatively minor for the unrecrystallized case but quite significant for the recrystallized case. This was manifested as a strong difference in the contraction of the surface layer compared to the centre of the extrudate, particularly in the case of tests at 45° and 90° to the extrusion direction. This was rationalized in terms of the differences in texture between the surface and the centre using VPSC simulations. Finally, it was proposed that this effect will be explored in future work as it may have important implications on the surface stress state which could affect damage initiation, growth and coalescence, particularly in bending situations.

A high-performance β-solidifying TiAl alloy sheet: Multi-type lamellar microstructure and phase transformation

TiAl alloys are widely used in the aerospace industry and, hence, a thorough understanding of the corresponding microstructural evolution is crucial for providing insight into the fabrication of high-performance TiAl alloy sheets. In this study, a high-performance β-solidifying Ti-43Al-9V-0.2Y alloy sheet with multi-type lamellar structures was obtained via hot-rolling at an initial rolling temperature of 1260 °C. Owing to the temperature drop and reheat associated with multi-pass rolling, relatively fine irregular β/γ and regular α2/γ lamellar microstructures (average size: ~25 μm) with nano-scaled antiphase domains (APDs) were generated by the β → γ and α + γ → α2 + γ/γT phase transformations. These two lamellar structures have different formation mechanisms. The results of electron backscatter diffraction and transmission electron microscopy revealed that the nucleation and growth of (i) β/γ and (ii) α2/γ lamellar structures are induced mainly by (i) stress and (ii) a combination of the stress and temperature drop during hot-rolling, respectively. Thin γT precipitates from the α/α2 or γ phases. This precipitation is induced by the higher stress and lower temperature associated with the later stage (compared with those occurring in the initial stages) of hot-rolling. Moreover, compared with the corresponding as-forged alloy, the as-rolled TiAl alloy sheet exhibits better performance at both room and elevated temperatures. The improvement in the tensile properties is attributed to the duplex microstructure consisting of fine multi-type lamellar structures with nano-scaled APDs. The interface boundaries of β/γ, α2/γ and APDs, which are effective in retarding dislocation motion, contribute mainly to strengthening of the alloy sheet.

Asymmetric rolling of interstitial free steel sheets: Microstructural evolution and mechanical properties

Asymmetric rolling (ASR) is a promising method for introducing shear deformation throughout the thickness of sheets. The induced shear deformation in ASR will result in texture evolution and which could also affect microstructural features controlling mechanical properties (such as the tensile strength). The main objective of this work consists of the investigation of the influence of ASR process on microstructure and texture evolution and their induced mechanical properties in interstitial free (IF) steel sheets. Both reverse and continuous asymmetric rolling were carried out to deform IF steel sheets. The results of optical microscopy observations showed no significant differences between the grain morphology of asymmetric and conventionally rolled (CR) samples. However, the obtained results of transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) indicated that fine and equiaxed microstructure was formed through the asymmetric rolling process. Texture evolution through plastic deformation has also been analyzed using X-ray diffraction. In addition, polycrystalline plasticity simulations were used to predict the texture evolution and the induced mechanical properties. The effect of the induced amount of pre-straining on the mechanical response of the samples through uniaxial tensile test has been studied. Results showed that at low thickness reductions (18%) the asymmetric rolled sample presents higher stress than that of the conventionally rolled sheet; while for higher thickness reductions (60%) the trend is reversed.

A Comparative Study on the Static Recrystallization Behavior of Cold-Rolled Mg-3Al-1Zn Alloy Stimulated by Electropulse Treatment and Conventional Heat Treatment

Cold-rolled AZ31 Mg alloy strips, with a reduction of 33 pct, were subjected to electropulse treatment (EPT) and conventional heat treatment (HT) to evaluate the respective influences of electropulses and temperature on the recrystallization behavior of AZ31. The highest measured temperature during the EPT (543 K) was used in HT. The electron backscattered diffraction results demonstrated that the EPT-stimulated recrystallization was completed within 8 seconds, whereas for HT, recrystallization was still far from completion even after 240 seconds. It was found that both the nucleation and grain growth of these two processes were totally different. In the EPT samples, nucleation tended to occur preferentially near extension twin boundaries and grain boundaries by continuous recrystallization, whereas in the HT samples, nucleation occurred mainly by grain boundaries bulging via discontinuous recrystallization. As grain growth proceeded, the texture intensities of the EPT samples decreased gradually and finally evolved into an obvious transverse-direction-split texture. This is likely attributable to the impact of electropulses on the boundary energy and the contribution of nonbasal dislocations; however, the basal-type textures of the HT samples were notably strengthened, which is associated with a 30 deg〈0001〉 orientation with respect to the deformed texture.

Two-dimensional strain-mapping by electron backscatter diffraction and confocal Raman spectroscopy

The strain field surrounding a spherical indentation in silicon is mapped in two dimensions (2-D) using electron backscatter diffraction (EBSD) cross-correlation and confocal Raman spectroscopy techniques. The 200 mN indentation created a 4 μm diameter residual contact impression in the silicon (001) surface. Maps about 50 μm × 50 μm area with 128 pixels × 128 pixels were generated in several hours, extending, by comparison, assessment of the accuracy of both techniques to mapping multiaxial strain states in 2-D. EBSD measurements showed a residual strain field dominated by in-surface normal and shear strains, with alternating tensile and compressive lobes extending about three to four indentation diameters from the contact and exhibiting two-fold symmetry. Raman measurements showed a residual Raman shift field, dominated by positive shifts, also extending about three to four indentation diameters from the contact but exhibiting four-fold symmetry. The 2-D EBSD results, in combination with a mechanical-spectroscopic analysis, were used to successfully predict the 2-D Raman shift map in scale, symmetry, and shift magnitude. Both techniques should be useful in enhancing the reliability of microelectromechanical systems (MEMS) through identification of the 2-D strain fields in MEMS devices.

Influence of hydrostatic extrusion process on the microstructure and texture of polycrystalline nickel

ABSTRACTThe evolution of the microstructure and texture of polycrystalline nickel, from its initial state to that after a hydrostatic extrusion process to total true strains of 0.5, 1.18, 1.62 and 2.2, were examined. Investigation of the microstructure revealed that the grain size was reduced from ∼32 µm to ∼200 nm. The local texture transformation and major boundary misorientation angles were discussed based on electron backscattered diffraction results, while XRD was used to give a qualitative and quantitative description of the global texture. Microhardness measurements were performed to investigate the changes in the mechanical properties of the deformed material.

Strain hardening behavior and deformation characteristics of multiphase microstructure in a medium-carbon quenching and partitioning bainitic steel

A 0.3C-1.4Si-1.8Mn (wt%) steel was subjected to a modified Q&P process leading to the formation of a multiphase microstructure comprising bainite, martensite and retained austenite. The strain hardening behavior and deformation characteristics of the multiphase microstructure were investigated by tensile tests and electron backscattered diffraction (EBSD), respectively. The results show that the multiphase microstructure containing about 50% bainite exhibits a better combination of strength (1617MPa), elongation (18.6%), the product of strength and elongation (PSE, 30.1GPa%) and toughness (103J) compared to the fully bainite. The strain hardening exponent-strain curves indicate that the multiphase microstructure has a much broader strain hardening plateau and the strain hardening exponent calculated for the multiphase microstructure and fully bainite is 0.085 and 0.064, respectively. The analysis results of EBSD demonstrate that the local stress concentration of the multiphase microstructure mainly appears in martensite and the bainite/martensite interfaces, and can more effectively spread to the interior of bainite with deformation increasing. In addition, the more low Taylor Factor regions under the large deformation condition and some retained austenite grain rotation can be observed in the multiphase microstructure. These caused better plastic deformation of multiphase microstructure with subsequent improvement in ductility.

On the martensitic structure and hardness in as-quenched Fe-Ni alloys

The martensitic transformation in dilute Fe-Ni alloys was firstly investigated by using a composition gradient in the range from 0 to 31 mass% Ni. The current study exhibited the transformation of austenite to equiaxed or acicular ferrite at lower Ni contents can be suppressed and lath martensite can form. The electron backscattered diffraction results showed Ni has important effect on misorientation distribution in martensite. With the increase of Ni content up to ∼27.5 mass%, the misorientation distributions above 15° increased, and a peak at around 7° gradually disappeared. With the further increase of Ni content, two peaks between about 50° and 60° at low Ni contents changed into three peaks at high Ni contents and a new peak at around 17° arose due to formation of plate martensite. Moreover, it was observed that both block and sub-block was refined with increasing Ni content. Moreover, the micro-hardness/strength of martensitic Fe-Ni alloys between previous works and this work and the micro-hardness of martensite between Fe-C and Fe-Ni alloys were compared and discussed.