Electron Backscatter Pattern Analysis Research Articles

Formation of cube recrystallized grains in high-purity Al

Abstract In high-purity 4 N (99.99 wt.%) Al containing 50 wt.ppm Cu, very strong {100}<001> recrystallization textures are developed after 98% cold rolling and annealing at 500 °C. They are about three times stronger than those observed in standard high-purity 4 N Al without Cu addition. In this paper, the mechanism of the formation of such strong {100}<001> recrystallization textures were investigated in detail by using the EBSP (electron backscatter pattern) analysis. It was found that, at the earliest stage of recrystallization, {100} <001>-recrystallized grains were nucleated by forming a row lying parallel to the rolling direction and growing preferentially within the elongated deformed grain in which they were nucleated. Most of these {100}<001>-recrystallized grains had orientations very near to the exact cube orientations. {100}<001>-recrystallized grains in this materials were characterized by their rapid growth, which was observed at the later stages of recrystallization. Since they were surrounded by deformed regions having very strong β-fiber rolling textures formed by heavy cold rolling, their grain boundaries were high-angle grain boundaries with high mobility. Assisted further by high stored energy introduced by heavy rolling reductions, {100}<001>-recrystallized grains could grow very rapidly, traversing readily several deformed grains. In this material, {100}<001>-recrystallized grains were not nucleated so abundantly. However, {100}<001>-recrystallized grains were nucleated much earlier and grew much faster than recrystallized grains with other orientations. They were, therefore, always larger than recrystallized grains with other orientations. Due to such size advantages, {100}<001>-recrystallized grains could rapidly consume fine-recrystallized grains with other orientations during the subsequent grain growth process. As a result, microstructures observed after annealing at 500 °C for 2 h consisted mostly of coarse {100}<001>-recrystallized grains slightly misoriented with each other. It is, thus, rapid growth of few {100}<001>-recrystallized grains during recrystallization, and their preferential grain growth, that enhance the development of very strong {100}<001> recrystallization textures in this high-purity Al. Cu seems to suppress nucleation of recrystallized grains with other orientations.

Heel crack propagation mechanism of cold-rolled Cu/Al clad ribbon bonding in harsh environment

A cold-rolled Cu/Al clad ribbon was bonded on an electroless nickel immersion gold (ENIG)-finished Cu substrate by ultrasonic bonding. The bonding samples were subjected to harsh conditions such as thermal exposure at 200 °C and thermal shock at −40/250 °C. The microstructural evolution and textural transitions in the Cu/Al clad ribbons were analyzed using electron backscatter diffraction to understand the heel crack propagation mechanism. The heel cracks were initiated at the edge of the Al layer between the bonded and non-bonded zones and were propagated along the coarsened grain boundaries deep into the cladded Cu layer. The continuous dynamic recrystallization (CDRX) transition phenomena around the heel cracks were scrutinized by electron backscatter pattern analysis to reveal the different microstructural and textural evolutions as a function of the ultrasonic bonding process at the bonded part and of lift-up at the non-bonded part. The heel cracks were occurred by grain coarsening due to CDRX within the Al layer during the environmental tests. The region of coarsened grains by CDRX was extended with increasing test periods. Especially in the thermal shock tests at −40/250 °C, severe grain coarsening was found involving significant transformation of sub-grains into grains by rapid CDRX development. Thus, heel crack propagation accelerated more during thermal shock cycles than during high-temperature storage.

Effect of Cold-Rolling Rate on Texture in Ti-Mo-Al-Zr Shape Memory Alloy

Effect of rolling rate on texure of Ti-Mo-Al-Zr shape memory alloy was investigated using X-ray diffraction pole figure measurement and electron backscattering pattern (EBSP) analysis to optimize the thermomechanical processing. Ti-Mo-Al-Zr alloy is a candidate Ni-free shape memory alloy to replace Ti-Ni alloy in medical applications. The alloy was single phase of β before rolling and then α''-martensite was induced during the cold-rolling. Unlike the recrystallization texture in Ti-Nb alloy system, {110}ββ recrystallization texture of β-phase was developed by the solution-treatment especially in the specimens with the reduction rate higher than 90%. This texture has never been observed in Ti-Nb based alloys and can exhibit a larger recovery strain in both tension and compression.

Correlation between the critical-current anisotropy and the microstructure of ex situ powder-in-tube processed MgB2 tapes

The MgB2 superconductor is a promising material for the coil conductors in the superconducting magnets. The anisotropy of the upper critical field of MgB2 is one of the limiting factors to the critical current density especially in the high magnetic field. The correlation between the critical current density and the microstructure of the MgB2 core part in the tape processed by the ex situ powder-in-tube method was investigated to obtain a clue for improving the critical current density values. The anisotropy in the field dependence of the critical current density was observed with respect to the angle between the applied magnetic field and the tape surface. Both the pole figure data in the x-ray diffraction analysis and the grain orientation map data in the electron back scattering pattern analysis indicated that the texture of the (001) plane occurred in the MgB2 core part of the tape quantitatively. This result suggests that the critical current density can be enhanced through the control of the microstructure of the MgB2 superconductor tapes.

Grain coarsening mechanism of Cu thin films by rapid annealing

Cu thin films have been produced by an electroplating method using nominal 9N anode and nominal 6N CuSO 4·5H 2O electrolyte. Film samples were heat-treated by two procedures: conventional isothermal annealing in hydrogen atmosphere (abbreviated as H 2 annealing) and rapid thermal annealing with an infrared lamp (abbreviated as RTA). After heat treatment, the average grain diameters and the grain orientation distributions were examined by electron backscattering pattern analysis. The RTA samples (400 °C for 5 min) have a larger average grain diameter, more uniform grain distribution and higher ratio of (111) orientation than H 2 annealed samples (400 °C for 30 min). This means that RTA can produce films with coarser and more uniformly distributed grains than H 2 annealing within a short time, i.e. only a few minutes. To clarify the grain coarsening mechanism, grain growth by RTA was simulated using the phase field method. The simulated grain diameter reaches its maximum at a heating rate which is the same order as that in the actual RTA experiment. The maximum grain diameter is larger than that obtained by H 2 annealing with the same annealing time at the isothermal stage as in RTA. The distribution of the misorientation was analyzed which led to a proposed grain growth model for the RTA method.

The effect of SiO 2 addition on the development of low-Σ grain boundaries in PTC thermistors

Electron backscatter pattern analysis has been used to characterise, using the coincidence site lattice model, the distribution of grain boundary structures in a series of BaTiO 3 based positive temperature coefficient of resistance (PTC) thermistors, prepared with 0, 1.0, 2.0 and 3.0 at.% SiO 2 additions. As the SiO 2 content was raised, the proportion of random, high-angle grain boundaries in the microstructure increased steadily from 85.7% to 89.6%, while the proportion of grain boundaries indexable in the range Σ3–Σ29 decreased from 14.3% to 10.4%, and the Σ3 grain boundary population fell from 5.9% to 3.6%. At the same time the proportion of Σ3 twin boundaries remained approximately constant at 3.0 ± 0.3%. Significantly more Σ3 grain boundaries than would be expected in a randomly oriented, untextured material were observed in all samples. The variation in grain boundary types with SiO 2 addition is discussed in terms of grain boundary energy and its effect on PTC performance.

冷間ECAE加工材の据込み時の割れ発生に及ぼす影響

The formability of steels subjected to different cold forming processes was investigated. In this study, the workability of ECAE(Equal channel angular extrusion) processed carbon steel was studied by cold upsetting tests. Three kinds of workpiece were prepared by ECAE process, rolling and combined (ECAE and post rolling) processes. All processes were carried out under the condition at room temperature. Experimental results are evaluated using cumulative equivalent strain. It was observed that the workability of the ECAE processed material was higher than that of the rolled one at the same equivalent strain. The higher workability was due to a continuous dynamic recrystallization which was identified by electron backscatter pattern (EBSP) analysis. The combined process enhanced mechanical properties and maintained good workability even with increasing applied strain, however its mechanism was not clarified.

Effect of the velocity of equal-channel angular pressing on the formation of the structure of pure aluminum

Transmission electron microscopy, X-ray diffraction, and electron back-scattering pattern analysis have been used to investigate the effect of the speed of equal-channel angular pressing (ECAP) at room temperature on the formation of ultrafine-grained structure in pure aluminum. It has been established that eight ECAP passages with a pressing speed of 3.3 × 10−2 mm/s results in the formation in aluminum of a substantially inhomogeneous grain structure with a grain size in the range of 1–27 μm (average size 3.0 μm). An increase in the speed of pressing by an order of magnitude leads to an increase in the level of internal stresses and dislocation density, an increase in the upper boundary of the interval of the grain-size distribution and in the average grain size (to 3.4 μm), and a decrease in the number of boundaries with high-angle misorientations. It is assumed that these changes are connected with the fact that processes of dislocation-structure relaxation have no time to occur during the ECAP at high pressing speeds.

Oriented Growth of Location-Controlled Si Crystal Grains by Ni Nano-Imprint and Excimer Laser Annealing

A new method of controlling the location and orientation of Si crystal grains by combining metal (Ni) nano-imprint and excimer laser annealing (ELA) using a double-layered Si thin-film structure was successfully demonstrated. Ni nano-imprint at the surface of the first amorphous Si (a-Si) film (25 nm thick) was performed to create {111}-oriented Si-crystal nuclei that act as the seed for the subsequent crystallization using ELA. The annealing that induces the formation of nuclei at the imprinted sites was carried out at temperatures below 450 °C to meet the requirement of low-temperature process. After the removal of Ni or Ni–silicide, the second a-Si film (75 nm thick) was deposited. XeCl-laser-based ELA of the sample resulted in the formation of approximately 2 µm sized Si crystal grains at controlled positions. Electron backscattering pattern (EBSP) analysis showed that the surface-normal orientation of all the location-controlled grains distributed less than 10° from <111 > crystal axis.

Ni基単結晶超合金の表面溶融部の組織学的検討

Crystal growth behavior in the surface-melted region of Ni-base single crystal superalloy CMSX-4 was investigated. The surface melting was conducted using 2kW diode laser or gas tungsten arc. Laser power and scanning speed in laser surface melting were varied while defocusing distance and shielding gas (Ar) flow rate were fixed. For arc surface melting, arc current and welding speed were varied. Specimen surfaces were arranged parallel to the (001) of the base metal. The microstructure and crystal orientation in the melted region were analyzed by using optical microscopy, scanning electron microscopy(SEM) and electron backscattered pattern analysis(EBSP). The microstructure and crystal orientation in laser surface-melted region were markedly influenced by heat input. The laser surface-melted region under low heat input conditions was found to be solidified as the single-crystalline state with unidirectional dendrites which grew along the [001] directions. The laser surface-melted region under intermediate heat input conditions was also single-crystalline with dendrites which grew along the [001], [010] and [100] directions. In contrast, in the case of high heat input conditions, the laser surface-melted region was consisted of polycrystal with stray crystals. Such tendencies were also observed in the melted region with gas tungsten arc. These results demonstrate that heat input significantly affects single-crystallinity regardless of the type of heat source, such as laser and arc. Furthermore, stray crystal formation in surface-melted region was investigated in detail by using SEM and EBSP. From the results of these experiments, it is revealed that stray crystal formation was affected by constitutional supercooling and dendrite growth direction.

Ni基単結晶超合金の表面溶融部の再結晶挙動と機械的特性

Recrystallization behavior in postheat treatment of the surface-melted regions of Ni-base single crystal superalloy CMSX-4 have been investigated. In, addition, mechanical properties of surface-melted regions after postheat treatment were evaluated. The surface melting was conducted using 2kW diode laser. The microstructure and crystal orientation in the melted regions were analyzed by using optical microscopy, scanning electron microscopy (SEM) and electron backscattered pattern analysis (EBSP). The effect of postheat treatment condition on microstructure was investigated using the specimens whose surface-melted regions were single-crystallized. The surface-melted regions were recrystallized when the temperature of postheat treatment was higher than 1513K. On the basis of this result, the partial solution treatment condition was proposed as 1493K×3.6ks to maintain single crystal structure without recrystallization in the surface-melted regions. Furthermore, the mechanical properties of surface-melted regions after partial solution treatment and subsequent aging were investigated by the creep rupture test. The creep rupture strength of surface-melted specimens was comparable to those of the base metal. It could be concluded that the crystalline controlled repairing technique would be applicable to the repair of single crystal superalloy turbine blades.

Inkjet Printing of Nickel Nanosized Particles for Metal-Induced Crystallization of Amorphous Silicon

We demonstrated for the first time single-crystal grain growth in the solid-phase crystallization of amorphous silicon (a-Si) film induced by inkjet-printed colloidal solution containing Ni nanosized particles. The electrostatic inkjet nozzle with a needle can print dots of Ni colloidal solution, whose size ranges from submicron order to a few ten micrometers, on the a-Si film surface by controlling the needle apex radius and the number of applied voltage pulses. The dependence of the crystallization behavior of a-Si on dot size is investigated by electron backscattering pattern (EBSP) analysis. Crystallization behavior is categorized into three modes: single-crystal growth, polycrystal growth, and lateral-crystal growth. Statistical analysis suggests that, when the dot size is 0.86 µm in diameter, a single-crystal grain is grown at the inkjet-printed sites with a probability of 0.62.

Effect of {0 0 1}〈1 1 0〉 texture on superelastic strain of Ti–Nb–Al biomedical shape memory alloys

Anisotropy in recovery strains was examined in a Ti–Nb–Al superelastic β-Ti alloy with a well-developed {0 0 1} β〈1 1 0〉 β texture. An ingot of Ti–24 mol% Nb–3 mol% Al alloy was fabricated by arc melting, homogenized at 1273 K for 7.2 ks, cold-rolled with 99% reduction in thickness and then solution-treated at 873 K for 3.6 ks. X-ray diffraction pole figure and electron backscatter pattern analysis revealed that {0 0 1} β〈1 1 0〉 β texture with grain size of 2 μm was developed in the alloy under the condition of the above thermo-mechanical treatment. Cyclic loading-unloading tensile test was made to evaluate superelastic properties. Tensile specimens were made with various orientation between the rolling direction (RD) and the longitudinal direction. Superelastic strain ( ɛ SE) was measured as the sum of the transformation strain ( ɛ TR) of β–α″ thermoelastic martensitic transformation and pure elastic strain ( ɛ E). It was found that ɛ TR at ϕ = 0° and 90° was almost the same and decreased to a minimum at around ϕ = 45°. On the other hand, it was found that ɛ E increased to a maximum at around ϕ = 45°. These orientation dependences of ɛ TR and ɛ E were in good agreement with the crystallography of the transformation and the anisotropy in Young's modulus in the alloy. ɛ SE was almost a constant regardless of ϕ. It was found that anisotropy in the tensile component of the superelastic strain available along the directions lying within the normal plane can be lowered by the development of the {0 0 1} β〈1 1 0〉 β texture.

Study of Microstructure in Surface-Melted Region of Ni-Base Single Crystal Superalloy CMSX-4

This work investigated microstructure in the surface-melted region of Ni-base single crystal superalloy CMSX-4 by using a diode laser beam as a heating source. Such processing parameters as laser power and scanning speed in laser surface melting were varied while defocusing distance and shielding gas (Ar) flow rates were fixed. Specimen surfaces were arranged parallel to the (001) of base alloy. The microstructure in the melted region was analyzed by optical microscopy and SEM. Crystal orientation of the melted region was analyzed using electron backscattered pattern analysis. The microstructure was remarkably changed when the heat input of surface melting was varied. The surface-melted region was found to solidify into a single crystal with directional dendrites that grew along the [001] directions under low heat input conditions. The surface-melted region was also a single crystal with disoriented dendrites that grew along the [100] or [010] directions under medium heat input conditions. In contrast, the melted region consisted of poly crystals with stray crystals under high heat input conditions. Such tendencies were also observed in the melted region with gas tungsten arc. These results demonstrate that the surface-melted region can solidify into a single crystal under conditions in which larger temperature gradient and higher solidification rates can be achieved.

Growth of bulk [formula omitted]- [formula omitted] crystals by annealing of well-aligned solidification structures

Bulk β - FeSi 2 crystals were grown by annealing of unidirectionally solidified structures with rods of the ε -FeSi in the α - FeSi 2 matrix. The crystallographic orientation of annealed samples was investigated by means of electron-backscattered pattern analysis. It was found that there were fibrous single crystals of β - FeSi 2 in the sample. The β - FeSi 2 crystal was easily grown along the solidification direction. The formation of the fibrous β - FeSi 2 single crystals resulted from limited nucleation at the initial stage.

Combination of Metal Nano-Imprint and Excimer Laser Annealing for Location Control of Si Thin-Film Grain

AbstractA novel method of locating Si thin-film grains by combining metal nano-imprint and excimer laser annealing (ELA) is demonstrated. Metal nano-imprint at the a-Si film surface is used for the purpose of creating Si crystal nuclei which act as the seed for the subsequent crystallization by using ELA. The annealing to form nuclei at imprinted sites was carried out at temperatures below 450oC. ELA using XeCl laser of the sample with capping SiOx film resulted in the formation of over 2.0 μm-sized Si crystal grains at controlled position. Electron back-scattering pattern (EBSP) analysis showed that about 75% of the boundaries inside the location-controlled grains were the coincidence site lattice boundaries.

Study on the Micro Mechanism of Recrystallization Texture Formation in Cold-Rolled IF Steel Sheet

An experimental setup was designed to study the recrystallization kinetics of Interstitial Free (IF) steel in this work. The 80% cold rolled IF steel foils are heated rapidly to 680°C, 730°C and 780°C by a salt bath. The recrystallization kinetic curves were obtained by the quantitative analysis of texture components, microstructures and EBSP (electron back-scattering patterns) measurements. With the help of EBSD, the orientations of the recrystallization nuclei are determined. The growth rule of the recrystallization nuclei was analyzed statistically. The effect of nucleus orientation on the formation of the recrystallization texture was investigated.

Cube Texture Development in Pure Ni during Annealing in a High Strength Magnetic Field

A 10 Tesla magnetic field was applied during annealing of cold-rolled high purity Ni at 300°C for 2 hours, with samples aligned at various different angles to the magnetic field direction. The effect of the magnetic field annealing on the cube texture evolution and the microstructural development was investigated by use of electron backscatter pattern (EBSP) analysis in the scanning electron microscope. The results show that both the cube texture evolution and the grain size are affected by the application during annealing of a high strength magnetic field, and that the effect varies as a function of the angle between the sample normal and the magnetic field direction. The cube texture volume fraction resulting from 2 hours annealing increases with increasing angle between the field direction and the sample normal direction, though in nearly all cases lower cube volume fractions were obtained compared to annealing without a magnetic field. The average size for all grains and for just cube-oriented grains both decrease with decreasing cube texture fraction, suggesting that the presence of a magnetic field either leads to enhanced recrystallization nucleation, or to a retardation of grain growth after recrystallization.

CHOICE OF Bi2223 UNIT CELL FOR TEXTURE STUDIES USING ORIENTATION DETERMINATION IN THE SCANNING ELECTRON MICROSCOPE

Existing proposals for the crystal structure of the high temperature superconducting Bi 2 Sr 2 Ca 2 Cu 3 O 7-x ( Bi 2223) phase have been reviewed. For the purpose of automated orientation determination in the scanning electron microscope using electron backscatter pattern (EBSP) analysis, a new crystal structure is proposed, where the unit cell is assumed to be tetragonal with P4/mmm point-group symmetry. Simulated EBSP images corresponding to the various unit cells exhibit significant differences, confirming the importance of choosing the correct unit-cell information. The suitability of various choices of the unit cell for automated orientation determination using EBSP analysis has been investigated using experimental data. The newly proposed unit cell is superior to the other unit cells for each of the criteria used to assess the indexing ability.

Formation and retention of low Σ interfaces in PTC thermistors

The distribution of grain boundary types in a barium titanate based positive temperature coefficient of resistance (PTC) thermistor was established using electron backscatter pattern analysis in a scanning electron microscope. A higher proportion of Σ = 3 interfaces than would be expected from a random grain distribution was observed, together with numerous Σ = 5 and Σ = 9 grain boundaries. All of these grain boundary types are reported in the literature to be PTC inactive, and hence should not contribute to the overall PTC response of the device. The Σ = 3 interfaces were further characterised on the basis of their microstructure as grain boundaries or annealing twins, from which it was established that the proportion of Σ = 3 grain boundaries in the thermistor increased only slightly during the sintering process, whereas the proportion of annealing twins increased significantly during the first 30 min of soak at the peak sintering temperature. Σ = 3 grain boundaries were found to be immobile during grain growth, in contrast with high angle grain boundaries, which showed considerable migration.