EBSD Results Research Articles

Flow softening, twinning and dynamic recrystallization in AZ31 magnesium

The compression tests were carried out on AZ31 magnesium alloy samples at temperatures from 300 to 450°C and strain rates of 0.03–0.3s−1. The evolution of the microstructure and texture was followed and the volume fractions recrystallized were determined as a function of strain and temperature. The flow curves were analyzed using the double differentiation method and double minima were detected on all the curves. The first set of minima is shown to identify the critical strain for twinning, while the second set indicates the critical strain for the initiation of dynamic recrystallization. The texture analysis and EBSD results indicate that flow softening is mainly caused by the grain reorientations brought about by twinning. The remainder of the flow softening is associated with the volume fraction recrystallized. The microstructure analysis shows that the volume fraction recrystallized does not approach its asymptotic value of one even during steady state flow.

Characterization of the microstructure and texture of functionally graded nickel-Al2O3 nano composite coating produced by pulse deposition

The main goal of this research was the characterization of the microstructure and texture of functionally graded nickel-Al2O3 nano composite coating. This coating was produced by changing the duty cycle under ultrasonic agitation during pulse deposition process. All of the electrodeposited layers were prepared at 20 A.dm−2 peak current density and constant frequency of 10Hz, and the duty cycle has been changed from 90% at the first layer to 10% at the fifth layer. According to SEM images and EBSD results, all layers except the last one showed a truncated pyramidal structure which is a typical morphology for Ni deposited coatings with [100] preferred texture. The last layer which was prepared at duty cycle of 10% exhibited a cauliflower (or colony) structure with small grains that probably resulted in random texture in this layer. EDS results showed more alumina particles can be incorporated at lower duty cycles. Foreign ions incorporation during the deposition process could be the reason for a change of [100] fiber texture to almost random orientation of grains. This rather high incorporation is due to either lower current density or higher OFF-Time duration at low duty cycles in pulse plating process.

The effect of heat treatment on crack control and grain refinement in laser beam welded β-solidifying TiAl-based alloy

Investigations were conducted on the γ-TiAl-based alloy Ti–42Al–2.5Cr–1Nb–0.7Si–0.5B (at. %) to assess the influence of in situ and conventional post-weld heat treatment on the microstructure and microtexture transformations induced by laser beam welding. It was found that in situ post-weld heat treatment at 800 °C was important to inhibit weld seam cracking. EBSD and HEXRD results indicated that the welding zone mainly consisted of coarse α2 “textured colonies”. These textured α2 are found to be in Burgers orientation relationship with their parent β grains. After 1 h of conventional post-weld heat treatment at 1200 °C followed by furnace cooling, the textured colonies are refined. The α2 grains nucleate heterogeneously on borides so that the sharp texture of the weld zone was broken down.

Effects of boundary characteristics on resistance to temper embrittlement and segregation behavior of Ni–Cr–Mo low alloy steel

SA508 Gr.4N Ni–Cr–Mo low alloy steel has higher strength and fracture toughness than those of commercial SA508 Gr.3 low alloy steel, due to its tempered martensitic microstructure as well as the solid solution effect and its higher contents of Ni and Cr. Hence, several studies have been performed on SA508 Gr.4N for nuclear application. In this study, the effects of microstructure on temper embrittlement and segregation behaviors in Ni–Cr–Mo low alloy steel were evaluated from the viewpoint of grain boundary characteristics. To evaluate the microstructural effect while excluding chemistry effects, the same heat was used but different microstructure samples were prepared by changing the cooling rate after austenitization. The increased volume fraction of martensite reduces the resistance to temper embrittlement, showing an increased transition-temperature shift (TTS) and increased P segregation at prior austenite boundaries. The segregation occurred intensively at prior austenite grain boundaries in tempered martensite, while the segregation occurred simultaneously at both prior austenite boundaries and packet boundaries in tempered bainite. In the EBSD results, most of the packet boundaries in tempered martensite are special boundaries such as ∑3 coincident site lattice (CSL) boundaries. The differences in P segregation between tempered martensite and tempered bainite are mainly caused by different portions of low energy special boundaries among the sub-grain boundaries. The reduction of temper embrittlement resistance in tempered martensite could be explained by the increased fraction of low energy CSL boundaries, which leads to a concentrated segregation of P at prior austenite grain boundaries.

Temperature dependence of strengthening mechanisms in the nanostructured ferritic alloy 14YWT: Part I—Mechanical and microstructural observations

This paper presents experimental results on the mechanical and microstructural behaviors of the nanostructured ferritic alloy 14YWT and provides discussion relevant to deformation mechanisms over a wide range of temperature. The temperature dependence of strength was investigated over a wide temperature range of −196 to 1000°C. Detailed microstructural characterization before and after deformation was conducted to obtain the key information on deformation mechanisms; microstructural information before and after tensile deformation, including crystallographic texture, dislocation structures, and nanoclusters, was obtained from the focused ion beam lift-out specimens using EBSD, TEM, and APT techniques. Multiple deformation stages could be identified in the yield strength versus temperature curve. The dislocation structures in the specimens deformed at room temperature and at 900°C were found to be significantly different. EBSD results were used to elucidate changes in the crystallographic textures of the specimens before and after deformation at 900°C.

The Tempering on Microstructure and the Yield-to-Tensile Ratio of High Performance Steels

The effects of tempering temperature on the microstructure and mechanical properties of 600MPa grade low carbon bainitic steel were investigated. The cause for the microstructure evolution has been investigated and the best tempering process was chosen to decrease the yield ratio of the steel. The influence of tempering process on the yield-to-tensile ratio of steels has been investigated by the aid of optical microscopy, SEM and XRD. The results show that after the TMCP processing the microstructure of steels mainly consist of lath martensite and bainite. The bainite and martensite have been refined markedly after the relaxation processing, therefore the properties of steels has been improved evidently. In order to decrease the yield-to-tensile ratio the steels underwent high temperature tempering. It has been found that during the tempering with the tempering temperature increased the yield-to-tensile ratio of steels decreased. The XRD and EBSD results show tempering temperature has considerable influence on the yield strength, but the influence on the tensile strength is not considerable. With the increase in tempering temperature, the low temperature toughness of steel can be improved considerably. The yield ratio of the steel was reduced after tempering at 650 °C and higher temperatures due to reversed austenitic phase transformation.

Influence of Crystallographic Texture on Young's Modulus of Various Alloy 82H Welds

Electron backscatter diffraction (EBSD) was employed to analyze the microstructure and texture of four different Alloy 82H gas tungsten arc welds that previously underwent static and dynamic modulus testing. The Young's moduli were shown to differ among the various welds, but also within each weld, dependent upon the direction measured. These differences were attributed to anisotropy of the crystallographic textures, which were described using inverse pole figures with respect to each of the weld's three orthogonal axes. The Young's modulus demonstrated a strong correlation with the texture, consistent with single crystal experiments. Sample directions containing a large population of {100} orientations had the lowest Young's modulus, while those with {111} grains possessed the highest. Microstructures with {110} textures were closer to the average modulus value of 207 GPa (30.0 Msi). X-ray diffraction texture measurements on four samples were used to verify the EBSD results.

Visualization of Hydrogen Diffusion in a Hydrogen-Enhanced Fatigue Crack Growth in Type 304 Stainless Steel

To study the influence of hydrogen on the fatigue strength of AISI type 304 metastable austenitic stainless steel, specimens were cathodically charged with hydrogen. Using tension-compression fatigue tests, the behavior of fatigue crack growth from a small drill hole in the hydrogen-charged specimen was compared with that of noncharged specimen. Hydrogen charging led to a marked increase in the crack growth rate. Typical characteristics of hydrogen effect were observed in the slip band morphology and fatigue striation. To elucidate the behavior of hydrogen diffusion microscopically in the fatigue process, the hydrogen emission from the specimens was visualized using the hydrogen microprint technique (HMT). In the hydrogen-charged specimen, hydrogen emissions were mainly observed in the vicinity of the fatigue crack. Comparison between the HMT image and the etched microstructure image revealed that the slip bands worked as a pathway for hydrogen to move preferentially. Hydrogen-charging resulted in a significant change in the phase transformation behavior in the fatigue process. In the noncharged specimen, a massive type α′ martensite was observed in the vicinity of the fatigue crack. On the other hand, in the hydrogen-charged specimen, large amounts of e martensite and a smaller amount of α′ martensite were observed along the slip bands. The results indicated that solute hydrogen facilitated the e martensitic transformation in the fatigue process. Comparison between the results of HMT and EBSD inferred that martensitic transformations as well as plastic deformation itself can enhance the mobility of hydrogen.

Accurate analysis of EBSD data for phase identification

This paper aims to investigate the reliability of software default settings in the analysis of EBSD results. To study the effect of software settings on the EBSD results, the presence of different phases in high Al steel has been investigated by EBSD. The results show the importance of appropriate automated analysis parameters for valid and reliable phase discrimination. Specifically, the importance of the minimum number of indexed bands and the maximum solution error have been investigated with values of 7–9 and 1.0–1.5° respectively, found to be needed for accurate analysis.

Dailies® AquaComfort Plus™ Significantly Improves Contact Lens-Related Symptoms in Patients Wearing Weekly to Monthly Soft Contact Lenses

The compression tests were carried out on AZ31 magnesium alloy samples at temperatures from 300 to 450 °C and strain rates of 0.03–0.3 s−1. The evolution of the microstructure and texture was followed and the volume fractions recrystallized were determined as a function of strain and temperature. The flow curves were analyzed using the double differentiation method and double minima were detected on all the curves. The first set of minima is shown to identify the critical strain for twinning, while the second set indicates the critical strain for the initiation of dynamic recrystallization. The texture analysis and EBSD results indicate that flow softening is mainly caused by the grain reorientations brought about by twinning. The remainder of the flow softening is associated with the volume fraction recrystallized. The microstructure analysis shows that the volume fraction recrystallized does not approach its asymptotic value of one even during steady state flow.

Sub‐structure characterization of experimentally and naturally deformed ice using cryo‐EBSD

In this work, we present first results of high-resolution EBSD for ice with a spatial resolution down to 0.25 microm. The study highlights the potential of EBSD to significantly increase our understanding of deformation and annealing processes associated with the build-up of internal stresses due to strain incompatibility between grains. Two polycrystalline samples were analyzed: a natural sample of polar ice from the Vostok ice core (Antarctica) and an experimentally deformed sample of laboratory grown columnar ice. In summary, we observe the following: (1) inhomogeneous deformation through the grains is translated into lattice distortions that are concentrated mainly at grain boundaries and triple junctions (natural and experimental sample), (2) these distortions may be continuous (natural and experimental sample) or may form distinct tilt boundaries and sub-grains of 10-50 microm size (experimental sample). These form mainly by rearrangement of basal edge dislocations into low-energy configurations (i.e. tilt boundaries) in various prism planes. Continuous lattice distortions originate from screw or mixed edge and screw dislocations lying in the basal plane.

Crystal Plasticity Finite Element Modelling of BCC Deformation Texture in Cold Rolling

Taylor-type and finite element polycrstal models have been embedded into the commercial finite element code ABAQUS to carry out the crystal plasticity finite element modelling of BCC deformation texture based on rate dependent crystal constitutive equations. Initial orientations measured by EBSD were directly used in crystal plasticity finite element model to simulate the development of rolling texture of IF steel under various reductions. The calculated results are in good agreement with the experimental values. The predicted and measured textures tend to sharper with an increase of reduction, and the texture obtained from the Taylor-type model is much stronger than that by finite element model. The rolling textures calculated with 48 {110}<110>, {112}<111> and {123}<111> slip systems are close to the EBSD results.

Overview of Texture Evolution during Friction Stir Welding of Stainless Steel Using Crystal Plasticity and EBSD

Texture evolution during friction stir welding of stainless steel was investigated using both predictions by crystal plasticity and EBSD measurements. Two- and three-dimensional Eulerian formulations are used to model friction stir welding. Plane strain deformation is assumed in a two-dimensional model, and an initial uniform texture changes into a torsion texture with monoclinic sample symmetry after deformation. Around the tool pin, the texture strengthens, weakens and restrengthens repeatedly. It is found from a simple circular streamline model that the relative magnitudes of the deformation rate and spin along the streamlines decide textural stability. In order to consider more complicated material behaviors, such as movement along the thickness direction due to a threaded tool pin and a tool shoulder, a three-dimensional Eulerian formulation is also implemented. Materials starting under the tool shoulder travel down to the bottom, producing the longest material streamlines. Those material points are predicted to have stronger texture components than others. EBSD results are compared with the predictions.

Monte Carlo Modelling of Recrystallization Process in Cold Rolled IF-Ti Steel

Recently, some authors have used the Monte Carlo modelling using complete set of experimental data to get a better correlation between experimental observations and calculations concerning recrystallization process [1, 2]. Simulations using Monte Carlo technique have been performed these last years for IF-Ti steels in order to predict the microstructure and the texture evolution after high reduction amounts by cold rolling [3, 4]. On the contrary, in the present work, this evolution is simulated in an IF-Ti steel cold rolled after low deformation amount (reduction amount R = 40 %). Microstructure is characterized by Electron Back-Scattered Diffraction and introduced in the model. The quality index of the Kikuchi patterns (EBSD data) is used to qualitatively evaluate the stored energy for each grain. Different hypothesis of nucleation mechanisms have been introduced into the model. It has been shown that the better recrystallization texture correlation between experiment and simulation is obtained by taking into account the nucleation in the low stored energy sites and highly misorientation regions. Finally a simulation issue was compared with EBSD and TEM experimental results: microstructure, recrystallization kinetics and Avrami coefficients values.

THE EVOLUTION OF TEXTURE AND GRAIN SIZE DURING ANNEALING OF NANOCRYSTALLINE Ni-45% Fe ELECTRODEPOSITS

The main goal of this research was the characterization of the microstructure and texture of functionally graded nickel-Al2O3 nano composite coating. This coating was produced by changing the duty cycle under ultrasonic agitation during pulse deposition process. All of the electrodeposited layers were prepared at 20 A.dm− 2 peak current density and constant frequency of 10 Hz, and the duty cycle has been changed from 90% at the first layer to 10% at the fifth layer. According to SEM images and EBSD results, all layers except the last one showed a truncated pyramidal structure which is a typical morphology for Ni deposited coatings with [100] preferred texture. The last layer which was prepared at duty cycle of 10% exhibited a cauliflower (or colony) structure with small grains that probably resulted in random texture in this layer. EDS results showed more alumina particles can be incorporated at lower duty cycles. Foreign ions incorporation during the deposition process could be the reason for a change of [100] fiber texture to almost random orientation of grains. This rather high incorporation is due to either lower current density or higher OFF-Time duration at low duty cycles in pulse plating process.