Electron Backscatter Diffraction Method Research Articles

Element-resolved Kikuchi pattern measurements of non-centrosymmetric materials

Angle-resolved electron Rutherford backscattering (ERBS) measurements using an electrostatic electron energy analyser can provide unique access to element-resolved crystallographic information. We present Kikuchi pattern measurements of the non-centrosymmetric crystal GaP, separately resolving the contributions of electrons backscattered from Ga and P. In comparison to element-integrated measurements like in the method of electron backscatter diffraction (EBSD), the effect of the absence of a proper 4-fold rotation axis in the point group of GaP can be sensed with a much higher visibility via the element-resolved Ga to P intensity ratio. These element-resolved measurements make it possible to experimentally attribute the previously observed point-group dependent effect in element-integrated EBSD measurements to the larger contribution of electrons scattered from Ga compared to P.

On the forbidden and the optimum crystallographic variant of rutile in garnet

In many inclusion–host systems with similar oxygen packing schemes, the optimum crystallographic orientation relationship (COR) between the inclusion and the host is mostly determined by matching the similar oxygen sublattices of the two structures. In contrast, the prediction of the optimum COR or even just the rationalization of the observed COR(s) between an inclusion and host with incompatible oxygen sublattices, like rutile–garnet, is not straightforward. The related documentation for such cases is therefore limited. Given the abundant crystallographic data for the rutile–garnet system acquired by transmission electron microscopy and electron backscatter diffraction methods recently, this problem can now be examined in detail for the critical structural factors dictating the selection of optimum COR in such a structurally complicated system. On the basis of the unconstrained three-dimensional lattice point match and structural polyhedron match calculated for the observed CORs, it becomes clear that the prerequisite of optimum COR for rutile (rt) in garnet (grt) is to have most of their octahedra similarly oriented/inclined in space by aligning 〈103〉rt and 〈111〉grt for needle extension growth. Further rotation along the 〈103〉rt//〈111〉grt direction then leads to the energetically most favorable COR-2 variant with a good lattice point match defined by the coincidence site lattice (CSL) and a good topotaxial match of the constituent polyhedra at the CSL points, leaving unfavorable COR-1′ in the forbidden zones. This understanding sheds light not only on hierarchical energetics for the selection of inclusion variants in a complicated inclusion–host system, but also on yet-to-be-explored [UVW]-specific CORs and hetero-tilt boundaries for composite materials in general.

Effect of Welding Heat Input on Microstructure and Texture of Inconel 625 Weld Overlay Studied Using the Electron Backscatter Diffraction Method

The grain size and the texture of three specimens prepared at different heat inputs were determined using optical microscopy and the electron backscatter diffraction method of scanning electron microscopy. Each specimen was equally divided into fusion line zone (FLZ), columnar dendrite zone (CDZ), and surface zone (SZ), according to the location of the weld. Fine dendrites were observed in the FLZ, coarse dendrites in the CDZ, and dendrites grew perpendicular to the FLZ and CDZ. As the heat input increased, the melted zone in the vicinity of the FLZ widened due to the higher Fe content. A lower image quality value was observed for the FLZ compared to the other zones. The results of grain size measurement in each zone showed that the grain size of the SZ became larger as the heat input increased. From the inverse pole figure (IPF) map in the normal direction (ND) and the rolling direction (RD), as the heat input increased, a specific orientation was formed. However, a dominant [001] direction was observed in the RD IPF map.

Structure and Properties of NiTi Shape Memory Alloy after Cold Rolling in Martensitic State

Due to unique features, like shape memory effects and superelasticity, NiTi alloys with nearly equiatomic composition are used in various branches of industry. Application of severe plastic deformation can drastically change properties of the materials. In the present paper the Ni50.4Ti49.6 alloy after cold rolling in the martensitic state and further annealed is studied. Phase transformations were studied using X-ray diffraction and differential scanning calorimetry measurements. Microstructure was examined using transmission electron microscopy and electron backscattering diffraction methods. Mechanical properties of obtained alloys has been studied using Vickers microhardness tests. Based on the performed measurements it can be seen that in studied alloys two steps B2 ↔ R ↔ B19′ phase transitions occurred. Performed plastic deformation influences course of phase transitions and phases composition. Due to the reduction of grain size microhardness of the studied material is increasing with increase of deformation degree.

Fatigue behavior of AZ31 magnesium alloy evaluated using single crystal micro cantilever specimen

Plane bending fatigue tests of magnesium alloy, AZ31, were conducted using micro cantilever specimens, which were composed of single crystals. The grain orientation of each specimen was analyzed by an electron back-scattered diffraction (EBSD) method. The slip and twin systems operated during fatigue tests were identified from the line analyses on the specimen surface. Depending on the crystallographic orientation, fatigue fracture modes were classified into three types, namely basal-slip, primary-twin and pyramidal-slip dominated fatigue. When the fatigue damage was dominated by pyramidal slip operation, the fatigue strengths were the highest. The lowest fatigue strengths were obtained in the basal-slip-dominated fatigue mode.

A Comparison on the EBSD and RO-XRD Techniques for Measuring Crystal Orientation of the Single-Crystal Ni-Based Superalloys

Measuring crystal orientation of a single-crystal Ni-based superalloy was conducted by two techniques of electron-backscattered diffraction (EBSD) and rotating-orientation x-ray diffraction (RO-XRD). Several single-crystal specimens were fabricated by Bridgman method at different withdrawal velocities. The misorientation of the preferred crystal orientation with the solidification direction of all specimens was characterized. A good match between the EBSD and RO-XRD methods was observed. The results showed an increasing trend of crystal misorientation with increasing withdrawal velocity.

A strain state in synthetic diamond crystals by the data of electron backscatter diffraction method

The authors put forward a procedure of determination of strain tensor components through the analysis of distribution of intensity of back-scattered electrons in Kikuchi patterns. The strain state has been studied in local areas of a synthetic diamond crystal produced by the temperature gradient method in the Fe–Al–C system through growing onto a diamond single crystal synthesized in the Ni–Mn–C system. Characteristic surfaces of the strain tensors and strain ellipsoids have been plotted; special features of strain distribution in the crystal have been analyzed. Diagonal tensor components have been determined from the changes of distributions of intensity of individual bands, the other components have been found from the displacements of axes of zones relative to their positions in the standard Kikuchi pattern.

Effect of crystal grain arrangement on fatigue crack initiation for Ni-based directionally solidified superalloy

Low cycle fatigue tests at elevated temperature were conducted on a Ni-based directionally solidified superalloy subjected to transverse loading. To investigate the effect of the arrangement and the orientation of crystal grains on the crack initiation, the electron backscatter diffraction (EBSD) method was applied on the surfaces of the tested specimens. In addition, finite element analysis that considered the plastic behaviour of crystal grains was performed to evaluate the relationship between the crack initiation and the local stress. The results are summarised below. Regarding the effect of crystallographic properties on the surface of specimens without holes, cracks generally initiated near the grain boundaries. In addition, most cracks initiated near the grain boundaries that neighboured the grain whose secondary axis was more inclined to the normal direction of specimen surface than the grain located in the opposite surface. Similarly, the number of cycles to crack initiation tended to be small along the hole edges located on the grain boundaries for the specimens with holes. The results of finite element analysis showed non-uniform stress distribution due to the grain orientation. They revealed that high longitudinal stress developed near the grain boundaries with cracks for the specimens without holes. Stress correlated with the number of cycles to crack initiation along hole edges for specimens with holes.

Metallurgical response of weld metal to different filler metal and joint design combinations of laser-arc hybrid welded lean duplex and novel ferritic stainless steels

Laser and laser-arc hybrid welding of duplex and ferritic stainless steels is demanding, because microstructure of the welds tends to be highly ferritic. Therefore, filler metal must be used for maintaining corrosion and mechanical properties of the welds. In this study, different filler metals including duplex, basic, and overalloyed austenitic grades were used with laser-arc hybrid method to weld lean duplex 1.4162 and novel ferritic stainless steels grades 1.4622 and 1.4509. Several sets of joint design and welding parameter combinations were used to adjust the amount of filler metal in the weld. The purpose of the trials was to evaluate whether weld metal microstructures (grain morphology, austenite/ferrite balance, etc.) can be modified by using an applicable joint preparation and an “overmatched” filler metal addition. Weld characterization included several research methods such as: Macro- and microscopic examination using light microscope¸ cross-sectional dilution ratio determination from the metallographic cross sections, electron backscatter diffraction method in order to assess austenite, and ferrite phase proportions in the test welds. The effects of used groove geometry, filler metal composition, and content on resulting metallurgical features of the welds are discussed in detail.

The effect of LPSO on the deformation mechanism of Mg–Gd–Y–Zn–Zr magnesium alloy

Abstract The tensile deformation behavior and corresponding microstructure evolution of the Mg-4.7Gd-3.4Y-1.2Zn-0.5Zr (at. %) magnesium alloy with long period stacking structure (LPSO) are studied by electron backscatter diffraction (EBSD) and slip lines methods. The results show that less and very small size of twins is observed in the grains with high value of Schmid factor for twinning, which indicates that the growth of the {10–12} twinning deformation is prevented by the LPSO phase. The prismatic lines present in grains of which the prismatic slip Schmid factor is above 0.4. The favorable orientation and LPSO phase synergistically promote the activation of prismatic slip. The inhomogeneous rotation of the grains during deformation is the reason for the microcrack at grain boundary.

Interactive effect of microstructure and cavity dimension on filling behavior in micro coining of pure nickel.

In this study, interactive effects of microstructure and cavity dimension on the filling behaviors in micro coining were investigated. The results indicate that the filling ability is dependent on both the cavity width t and the ratio of cavity width to grain size t/d strongly. The critical ratio t/d for the worst filling ability increases with cavity width t and tends to disappear when the cavity width t increases to 300 μm. A polycrystalline filling model considering the friction size effect, effect of constrained grains by the tools, grain size, cavity width and ratio of cavity width to grain size is proposed to reveal the filling size effect in micro coining. A quasi in-situ Electron Backscatter Diffraction (EBSD) method is proposed to investigate filling mechanism in micro coining. When several grains across the cavity width, each grain deforms heterogeneously to ordinate the deformation compatibility. When there is only one grain across the cavity width, the grain is fragmented into several smaller grains with certain prolongation along the extrusion direction to coordinate the deformation in the cavity. This is different from the understandings before. Then the filling deformation mechanism is revealed by a proposed model considering the plastic flow in micro coining.

A Physically Based Dynamic Recrystallization Model Considering Orientation Effects for a Nitrogen Alloyed Ultralow Carbon Stainless Steel during Hot Forging

The nitrogen alloyed ultralow carbon stainless steel is a good candidate material for primary loop pipes of AP1000 nuclear power plant. These pipes are manufactured by hot forging, during which dynamic recrystallization acts as the most important microstructural evolution mechanism. A physically based model was proposed to describe and predict the microstructural evolution in the hot forging process of those pipes. In this model, the coupled effects of dislocation density change, dynamic recovery, dynamic recrystallization and grain orientation function were considered. Besides, physically based simulation experiments were conducted on a Gleeble-3500 thermo-mechanical simulator, and the specimens after deformation were observed by optical metallography (OM) and electron back-scattered diffraction (EBSD) method. The results confirm that dynamic recrystallization is easy to occur with increasing deformation temperature or strain rate. The grains become much finer after full dynamic recrystallization. The model shows a good agreement with experimental results obtained by OM and EBSD in terms of stress-strain curves, grain size, and recrystallization kinetics. Besides, this model obtains an acceptable accuracy and a wide applying scope for engineering calculation.

Combining the Electrochemical Microcell Technique and the Electron Backscatter Diffraction method to study the electrochemical behaviour of polycrystalline aluminium in sodium chloride solution

The corrosion behaviour of pure aluminium was studied at the microscale in 0.1M NaCl by combining the electron backscatter diffraction technique and the electrochemical microcell technique. The microstructure was first described. It was found that plastic strain has little influence on these microstructural parameters. After surface preparation, the crystallographic orientation of grains plays a significant role in their corrosion behaviour. Grains oriented along (001) planes are the most resistant to pitting corrosion whereas those oriented along (111) planes are the most susceptible to pitting. After plastic deformation, the susceptibility to pitting corrosion of Al grains is significantly increased and there is no influence of the crystallographic orientation of grains. It was proposed that the presence of a high density of statistically stored dislocations (which cannot be detected by EBSD) affects the physical chemical properties of the oxide film formed on grains. This oxide film degenerates, leading to high susceptibility of pure Al to pitting corrosion.

Microstructural Development around Crater in Commercial Pure Titanium

The commercial pure titanium plate was shot vertically by the projectile with a diameter of 7.62mm at impact velocities ranging from 782m/s to 825m/s. The microstructure around the crater of commercial pure titanium plate was analyzed by optical microscopy (OM) and electron backscatter diffraction (EBSD) methods. It was found that different microstructures were observed along the depth of cater. In upper region of the crater, grains were deformed and fragmented. Adiabatic shear bands (ASBs) were observed in the middle of the crater, and some ASBs were bifurcated. At the bottom of the crater, the grains were less deformed, and the deformation twins were formed. The microstructures in the center of adiabatic shear band were mainly consisted of the dynamic recrystallization grains and sub-grains. The microstructure in the transition region was elongated grains along the shear stress distribution.

Advanced fabrication of single-crystalline silver nanopillar on SiO2 substrate

Nanoscale crystallographic textures have received very little attention in research on surface plasmons using metallic nanostructures. A single-crystalline metallic nanostructure with a controlled crystallographic texture is expected to reduce optical losses. We elucidated the grain growth mechanism in silver thin films deposited on a highly transparent SiO2 substrate by electron backscatter diffraction methods with nanoscale resolution. At higher substrate temperatures, the grain growth was facilitated but the preferred orientation was not achieved. Moreover, we fabricated a single-crystalline silver nanopillar in a (111)-oriented large growing grain, which was controlled by varying the substrate temperature during film deposition by focused ion-beam milling. Furthermore, the light intensity of the scattering spectrum was measured for a single-crystalline silver nanopillar (undersurface diameter: 200 nm) for which surface plasmon resonance was observed. The single-crystalline silver nanopillar exhibits a stronger and sharper spectrum than the polycrystalline silver nanopillar. These results can be applied to the direct fabrication of a single-crystalline silver nanopillar using only physical processing.

Texture evolution during static recrystallization of cold-rolled magnesium alloys

Texture evolution in cold-rolled Mg-0.3Zn-0.1Ca, Mg-0.4Zn and Mg-0.1Ca (at.%) alloys during static recrystallization is monitored using a quasi-in-situ electron backscatter diffraction (EBSD) method. The quasi-in-situ EBSD results show that most of recrystallized grains formed in the early stage of recrystallization have randomised orientations in the ternary alloy and they grow uniformly during the recrystallization process. The formation and uniform growth of these recrystallized grains with randomised orientations give rise to a weak texture in fully recrystallized samples of the ternary alloy. A weak recrystallization texture also forms in the early stage of recrystallization in the two binary alloys, but it is gradually replaced by a strong basal texture via the preferential growth of recrystallized grains with specific orientations. The grain size in the ternary alloy is smaller than those in the two binary alloys at each stage of recrystallization, and the grain size distribution in the ternary alloy is significantly narrower than those in the two binary alloys after full recrystallization. Solute segregation to grain boundaries is observed in all three alloys in the fully recrystallized state. It is hypothesised that Zn and Ca atoms in the ternary alloy segregate strongly to high-energy boundaries of the recrystallized grains that would otherwise grow preferentially in the counterpart binary alloys, and that this co-segregation would significantly reduce the boundary mobility, by reducing grain boundary energy and enhancing solute dragging effect, and therefore lead to a more uniform growth of recrystallized grains with randomised orientations.

Development of biodegradable occlusion device using ductile magnesium-zinc-calcium alloy

Development of biodegradable occlusion device using ductile magnesium-zinc-calcium alloy

微小孔を有するNi基一方向凝固超合金の高温低サイクル疲労き裂発生に対する結晶特性の影響評価

Low cycle fatigue tests at elevated temperature were conducted on a Ni-based directionally solidified superalloy with small holes subjected to transverse loading. To investigate the effect of the arrangement and the orientation of crystal grains on the crack initiation, the electron back-scatter diffraction (EBSD) method was applied on the surface of the tested specimens. In addition, finite element analysis that considered the plastic behavior of crystal grains was performed to evaluate the relationship between the crack initiation and the local stress that developed along the hole edges. The results are summarized below. It was shown that the number of cycles to crack initiation tended to be small along the hole edges located on the grain boundaries by classifying the hole edges according to the position of the hole edge and the grain boundary. In addition, it was small along the hole edges located in the grain whose secondary axis was more inclined than the grain located in the opposite surface. The results of FEM analysis revealed that high stress developed along those hole edges. The location where high stress developed correlated with the number of crack initiation cycles not only among the hole edges in one specimen but also among the specimens subjected to different nominal strain range.

Quantification of Large Deformation with Punching in Dual Phase Steel and Change of its Microstructure –Part II: Local Strain Mapping of Dual Phase Steel by a Combination Technique of Electron Backscatter Diffraction and Digital Image Correlation Methods

Quantification of Large Deformation with Punching in Dual Phase Steel and Change of its Microstructure –Part II: Local Strain Mapping of Dual Phase Steel by a Combination Technique of Electron Backscatter Diffraction and Digital Image Correlation Methods

DP鋼の打抜き大変形の定量的評価とそのミクロ組織変化(第2報)−電子線後方散乱法とデジタル画像相間法を組み合わせたDP鋼の局所ひずみマッピング−

DP鋼の打抜き大変形の定量的評価とそのミクロ組織変化(第2報)−電子線後方散乱法とデジタル画像相間法を組み合わせたDP鋼の局所ひずみマッピング−