Showing papers on "Electron backscatter diffraction published in 2009"

Reinvestigation of Li2MnO3 Structure: Electron Diffraction and High Resolution TEM

Abstract: The structure of Li2MnO3 was investigated by the means of X-ray and electron diffraction as well as high resolution transmission electron microscopy experiments. Extra spots are present in the Li2MnO3 electron diffraction patterns, and their origin is fully understood and explained here. They result from the existence of diffuse scattering lines observed along the c* monoclinic axis, intercepted by the Ewald’s sphere, and not from double diffraction phenomenon nor from superstructure. Furthermore, the origin of these scattering lines is due to stacking faults of the ordered lithium/manganese layers along the c-axis that were observed in images obtained using high resolution transmission electron microscopy.

Microstructural evolution in pure aluminum processed by high-pressure torsion

Abstract: Pure Al (99.99%) was processed using high-pressure torsion (HPT), and Vickers microhardness was measured along the diameter of the disk samples. When all hardness values were plotted as a function of equivalent strain, they fell on a single line having three distinctive regions. The hardness increases with the strain in the first region and, after taking a maximum at an equivalent strain of ∼2, the hardness decreases with further straining in the second region. The third region appears at an equivalent strain of ∼6 or higher as a steady state where the hardness remains unchanged. Electron backscatter diffraction analysis and transmission electron microscopy were conducted in the corresponding regions and microstructural evolution with straining was examined. Grain refining mechanism using HPT was discussed based on the change in the hardness and microstructures.

Orientational analysis of static recrystallization at compression twins in a magnesium alloy AZ31

Abstract: In contrast to cubic metals, the dominant recrystallization nucleation site of hexagonal magnesium is compression twins or the shear bands evolved from them. In this paper, we determine the macrotextures and microstructures of a magnesium alloy AZ31 during static recrystallization. We interpret these data according to a microtexture analysis performed with the EBSD technique of new grains formed at compression twins in the early stage of static recrystallization. The results show that the orientation characteristics in local regions during nucleation are similar to those of subgrains within compression twins or shear bands. However, the new grains mainly take the orientations of the subgrains, which have been subjected to complicated orientation rotations. This phenomenon is attributed to the large amount of their stored energy. Despite the difference between new grain orientations and those of the deformed matrix, the retained deformation texture after annealing is explained mainly by the incomplete recrystalization of magnesium.

Microstructural Evolution of a Low-Carbon Steel during Application of Quenching and Partitioning Heat Treatments after Partial Austenitization

Abstract: The “quenching and partitioning” (Q&P) process has been studied in a low-carbon steel containing 1.1 wt pct aluminum by heat treatments consisting of partial austenitization at 900 °C and subsequent rapid cooling to a quenching temperature in the range between 125 °C and 175 °C, followed by an isothermal treatment (partitioning step) at 250 °C and 350 °C for different times. Characterization by means of optical and scanning electron microscopy, electron backscattered diffraction (EBSD), magnetization measurements, and X-ray diffraction (XRD) has shown a multiphase microstructure formed by intercritical ferrite, epitaxial ferrite, retained austenite, bainite, and martensite after different stages of tempering. A considerable amount of retained austenite has been obtained in the specimens partitioned at 350 °C for 100 seconds. Experimental results have been interpreted based on concepts of the martensite tempering, bainite transformation, and kinetics calculations of the carbon partitioning from martensite to austenite.

Improved precision in strain measurement using nanobeam electron diffraction

Abstract: Improvements in transmission electron microscopy have transformed nanobeam electron diffraction into a simple and powerful technique to measure strain. A Si0.69Ge0.31 layer, grown onto a Si substrate has been used to evaluate the precision and accuracy of the technique. Diffraction patterns have been acquired along a ⟨110⟩ zone axis using a FEI-Titan microscope and have been analyzed using dedicated software. A strain precision of 6×10−4 using a probe size of 2.7 nm with a convergence angle of 0.5 mrad has been reached. The bidimensional distortion tensor in the plane perpendicular to the electron beam has been obtained.

Growth of intermetallic layer in the aluminide mild steel during hot-dipping

Abstract: Mild steel was coated by hot-dipping in a molten aluminum bath. The growth behavior in the intermetallic layer after various times of immersion in the hot-dip at 700 °C was analyzed by electron backscatter diffraction (EBSD). The results showed that the aluminide layer consisted of an outer aluminum topcoat, minor FeAl 3 and major Fe 2 Al 5 , respectively. From another perspective, Fe 2 Al 5 possessed a tongue-like morphology, which caused the corresponding serration-like morphology of the steel substrate. The Fe-Al/steel substrate interface of the Fe 2 Al 5 phase, after removal of the steel substrate, displayed a columnar structure growing toward the steel substrate, implying that Fe 2 Al 5 grew at a rapid rate along the diffusion direction. Moreover, the EBSD results revealed the Fe 2 Al 5 phase was not only composed of columnar grains, but also possessed fine grains clustered around the peaks of the serration-like steel substrate.

Synthesis and toluene sensing properties of SnO2 nanofibers

Abstract: A simple method for the large-scale synthesis of SnO2 nanofibers has been demonstrated through an electrospinning method. The as-synthesized fibers are characterized by scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, X-ray diffraction, and energy dispersive X-ray analysis. The sensor fabricated from these fibers exhibits high response to toluene at 350 ◦ C with good selectivity. The response time and recovery time are about 1 and 5 s, respectively. The linear dependence of the response value on the toluene concentration is observed in the range of 10–300 ppm. The potential application of SnO2 nanofibers for fabricating high performance toluene sensors at industry level has been demonstrated. © 2008 Elsevier B.V. All rights reserved.

Study of high strength pipeline steels with different microstructures

Abstract: In the present study, comparison studies on mechanical properties were made on a commercial X70 grade polygonal ferrite (PF) dominated pipeline steel and a laboratory developed X90 grade acicular ferrite (AF) dominated pipeline steel obtained by optimum thermo-mechanical controlled processing (TMCP). Charpy impact test results indicated that the upper shelfenergy (USE) of the AF pipeline steel was a little bit higher, but its energy transition temperature (ETT) was extremely low, about -162 degrees C, much lower than that of the PF pipeline steel of about -121 degrees C. It was analyzed that higher strength and better toughness of the AF pipeline steel came from its finer grain size and higher density of dislocations and subboundaries, which could be also further proved from the electron backscatter diffraction (EBSD) analysis for its finer effective grain size (EGS) and higher content of low angle grain boundaries (LAGBs), smaller cleavage fracture unit measured from the fracture surface around fracture origin fractured at -196 degrees C, and its more bent crack propagation path in the fracture. (C) 2008 Elsevier B.V. All rights reserved.

Ultrafine Grain Refinement of Biomedical Co-29Cr-6Mo Alloy during Conventional Hot-Compression Deformation

Abstract: In order to examine the microstructural evolution during hot-compression deformation of the biomedical Co-29Cr-6Mo (weight percent) alloy without the addition of Ni, hot-compression tests have been conducted at deformation temperatures ranging from 1050 °C to 1200 °C at various strain rates of 10−3 to 10 s−1. The grain refinement due to dynamic recrystallization (DRX) was identified under all deformation conditions by means of field-emission scanning electron microscopy/electron backscattered diffraction (FESEM/EBSD) and transmission electron microscopy (TEM) observations. Although the DRX grain size (d) of the deformed specimens considerably decreased with an increasing Zener–Hollomon (Z) parameter at strain rates ranging from 10−3 to 0.1 s−1, a grain size coarser than that predicted from the d-Z relation was obtained at strain rates of 1.0 and 10 s−1. An ultrafine-grained microstructure with a grain size of approximately 0.6 μm was obtained under deformation at 1050 °C at 0.1 s−1, from an initial grain size of 40 μm. The grain refinement to a submicron scale of biomedical Co-Cr-Mo alloys has been achieved with hot deformation by ~60 pct due to DRX, in which the bulging mechanism is not operative. The ultrafine grains obtained due to DRX without bulging is closely related to the considerably low stacking-fault energy (SFE) of the Co-Cr-Mo alloy at deformation temperatures.

Characterization of the Grain-Boundary Character and Energy Distributions of Yttria Using Automated Serial Sectioning and EBSD in the FIB

Abstract: A dual-beam focused ion beam scanning electron microscope was used to collect a series of parallel electron backscatter diffraction maps of polycrystalline yttria. Using characteristics of the triple junctions, the individual layers were aligned and the geometries of the grain-boundary planes between the layers were determined. This information was used to calculate the five-parameter grain-boundary character distribution (GBCD) and grain-boundary energy distribution (GBED). The GBCD derived from the three-dimensional data was qualitatively the same as that derived from a stereological analysis of the same data. The anisotropy in the GBCD of yttria is relatively weak compared with other ceramics and is inversely correlated to the GBED.