3DXRD Microscopy Research Articles

The emergence of super-resolution beyond the probe size in scanning 3DXRD microscopy.

The spatial resolution in scanning-based two-dimensional microscopy is normally limited by the size of the probe, thereby a smaller probe is a prerequisite for enhancing the spatial resolution. For three-dimensional microscopy that combines translation and rotation motions of a specimen, however, complex trajectories of the probe highly overlap in the specimen, which could change the postulate above. Here, the spatial resolution achieved in scanning three-dimensional X-ray diffraction (s3DXRD) microscopy is investigated. In this method, the most appropriate orientation of the pixel in the specimen coordinate is selected by comparing the completeness of diffraction peaks with theory. Therefore, the superposed area of the beam trajectory has a strong effect on the spatial resolution, in terms of the completeness of diffraction peaks. It was found that the highly superposed area by the incident X-rays, which has the highest completeness factor in the pixel of the specimen, is much smaller than the X-ray probe size, and that sub-pixel analysis by dividing a pixel into small pieces leads to drastic improvement of the spatial resolution ins3DXRD.

Inclined scanning 3DXRD microscopy for high-resolution 3D grain orientation mapping

Inclined scanning 3DXRD microscopy for high-resolution 3D grain orientation mapping

Novel Near Field Detector for Three-Dimensional X-Ray Diffraction Microscopy

Three dimensional X-ray diffraction (3DXRD) microscopy is a powerful technique that provides crystallographic and spatial information of a large number, of the order of thousands, of crystalline grains in a sample simultaneously. A key component of every 3DXRD microscopy experiment is the near field detector that provides high resolution spatial information of the grains. In this work we present a novel design for a semi-transparent, 16 megapixel near field detector. As opposed to a typical single scintillator phosphor detector, this design, we call the Quad Near Field Detector, uses four quadrants. It has a total field of view is 5.3 mm x 5.3 mm with an effective pixel size of 1.3 µm x 1.3 µm. The detector’s relatively large field of view can be used to obtain higher order diffraction spots which we anticipate will lead to improved spatial resolution in grain reconstructions. The large field of view can also enable the detector to be positioned further from the sample, in this way increasing the working distance and enabling larger environmental cells for in-situ studies. Many alignment parameters can be resolved by careful mechanical design. For this reason a novel translation stage for focusing the microscopes was developed, tested, and implemented. The near field detector was calibrated and characterized at the Cornell High Energy Synchrotron Source. The operational feasibility of such a multi-plate detector demonstrated in this work paves the way for new technologies in instrumentation of 3DXRD microscopy.

Formation of (Fe,Cr) carbides and dislocation structures in low-chromium steel studiedin situusing synchrotron radiation

The evolution of the size distribution of (Fe,Cr) carbides and the dislocation structure in low-chromium steel is studied during quenching and rapid heating byin situsmall-angle X-ray scattering (SAXS). The two-dimensional SAXS patterns consist of streaks on top of an isotropic SAXS signal. The evolution of the size distribution of the (Fe,Cr) carbides during heat treatment is determined from the isotropic component of the SAXS patterns. The isotropic part of the SAXS patterns shows that, after austenitization and quenching to room temperature, the average precipitate radius is 4.74 nm and the dispersion parameter for the lognormal size distribution is 0.33. Subsequent rapid heating to 823 K results in an average precipitate size of 5.25 nm and a dispersion parameter of 0.26. Bright-field transmission electron microscopy and high-resolution transmission electron microscopy reveal the nearly spherical morphology of the precipitates. The microstructural evolution underlying the increase in the average precipitate size and the decrease in the dispersion parameter after heating to and annealing at 823 K is probably that at room temperature two types of precipitates are present,i.e.(Fe,Cr)23C6and (Fe,Cr)7C3precipitates according to thermodynamic calculations, and at 823 K only (Fe,Cr)7C3precipitates are present. Additional measurements have been carried out on a single crystal of ferrite containing (Fe,Cr) carbides by combining three-dimensional X-ray diffraction (3DXRD) and SAXS during rotation of the specimen at room temperature, in order to investigate the origin of the streaks at low angles in the SAXS pattern. From simulations based on the theory of SAXS from dislocations, it is shown that the measured streaks, including the spottiness, in the two-dimensional SAXS patterns correspond to a dislocation structure of symmetric low-angle tilt boundaries, which in turn corresponds to the crystallographic orientation gradient in the single crystal of ferrite as measured by 3DXRD microscopy.

A fast methodology to determine the characteristics of thousands of grains using three-dimensional X-ray diffraction. I. Overlapping diffraction peaks and parameters of the experimental setup

A data-analysis methodology is presented for the characterization of three-dimensional microstructures of polycrystalline materials from data acquired using three-dimensional X-ray diffraction (3DXRD). The method is developed for 3DXRD microscopy using a far-field detector and yields information about the centre-of-mass position, crystallographic orientation, volume and strain state for thousands of grains. This first part deals with pre-processing of the diffraction data for input into the algorithms presented in the second part [Sharma, Huizenga & Offerman (2012).J. Appl. Cryst.45, 705–718] for determination of the grain characteristics. An algorithm is presented for accurate identification of overlapping diffraction peaks from X-ray diffraction images, which has been an issue limiting the accuracy of experiments of this type. The algorithm works in two stages, namely the identification of overlapping peaks using a seeded watershed algorithm, and then the fitting of the peaks with a pseudo-Voigt shape function to yield an accurate centre-of-mass position and integrated intensity for the peaks. Regions consisting of up to six overlapping peaks can be successfully fitted. Two simulations and an experiment are used to verify the results of the algorithms. An example of the processing of diffraction images acquired in a 3DXRD experiment with a sample consisting of more than 1600 grains is shown. Furthermore, a procedure for the determination of the parameters of the experimental setup (global parameters) without the need for a calibration sample is presented and validated using simulations. This is immensely beneficial for simplifying experiments and the subsequent data analysis.

NON-DESTRUCTIVE IDENTIFICATION OF MICROMETER-SCALE MINERALS AND THEIR POSITION WITHIN A BULK SAMPLE

Using the conventional techniques of mineralogy, it has been a challenge to determine mineral identity, crystal orientation and spatial position of micrometer-sized crystals that are embedded in a rock, sediment or soil. Traditionally, the individual grains must be extracted and analyzed separately. Crushing or disintegrating a sample annihilates any possibility for gathering information from the texture of the porous media or the mineral assemblage close to the grains in question. A new method using three-dimensional X-ray diffraction (3DXRD) microscopy can be successfully applied to natural materials. We combined X-ray microtomography (XMT) and 3DXRD to investigate a sample of very fine-grained chalk containing fracture minerals. The XMT technique provides three-dimensional images of the particles and pore structure at very high resolution (350 nm voxel dimension) on samples less than 500 μm in diameter. The minor phases present as crystals in fractures were determined nondestructively with 3DXRD microscopy. The chalk fragment investigated is composed predominantly of randomly oriented nanometric crystals of calcite that produce powder rings where no texture can be observed. Superimposed on this pattern, Bragg diffraction peaks from the other crystalline phases were observed. Individual crystals of barite and pyrite only a few micrometers in diameter are present in the fractures. Magnetite, celestine and siderite, other minerals that might have been expected based on the XMT absorption contrast, were not identified. The crystal shape and in-fracture location, derived from the microtomograms, and the mineral identity, derived from 3DXRD, allowed us to propose that the fractures are original in these tiny drill cuttings; they were not induced by drilling and filled with drilling mud particles, thus allowing reliable estimates to be made of rock porosity and permeability.

Following individual grains during solid-state phase transformations with 3DXRD microscopy

Abstract The mechanical properties of metals strongly depend on the microstructure, which is formed during their production and processing. Understanding the underlying mechanisms of the nucleation and growth kinetics during solid-state phase transformations in steel is of vital importance to control its microstructure. The kinetics of individual grains in the bulk of steel can be measured in situ with the three-dimensional X-ray diffraction microscopy (3DXRD) at the European synchrotron radiation facility (ESRF). Simultaneously the fraction transformed, the nucleation rate, and the growth rate of individual grains can be measured. Unique in situ measurements of nucleation and growth rates of individual austenite and ferrite grains are presented.

In-situ observation of the nucleation kinetics and the mechanism of grain refinement in Al–Si alloys (Part I)

The nucleation behavior of primary aluminium phase in a hypoeutectic Al–Si foundry alloy is studied using the 3DXRD microscope during the liquid–solid phase transformation for continuous cooling. Grain nucleation and grain growth for few different casting conditions of a commercial aluminium alloy (A356: Al-7Si-0.4 Mg-0.1Fe-0.1Ti wt.%) were investigated using three dimensional X-ray diffraction microscope (3DXRD) located at ID11 at European Synchrotron Radiation Facility ( www.ESRF.eu). To conduct the study a monochromatic hard X-ray beam (energy of 70 keV) with a beam size of 200×200 µm 2 was used and using a special furnace the microstructure evolution during solidification of a commercial Al–Si foundry alloy (A356) was monitored in-situ. Results gathered from solid fraction information showed adding 0.1 wt.% Ti (as Al-3Ti-B) changes the primary aluminium nucleation temperature and aluminium grain size. Furthermore, it showed that at slower cooling rate (0.04–0.1 K/s) grain refiner can alter the primary aluminium nucleation temperature by 20 °C, whereas at higher rates (2 K/s) this figure was reduced down to 5 °C.

Growth of Individual Austenite Grains Measured with 3DXRD Microscopy

Studying austenitisation in steel, so far, was either limited to observations at the surface of the material or to the determination of the average grain growth behavior in the bulk. The development of the three-dimensional X-ray diffraction (3DXRD) microscope at beam line ID11 of the European Synchrotron Radiation Facility in Grenoble, France, made it possible to study the transformation kinetics in-situ and at the level of individual grains in the bulk of the material. Unique in-situ observations of austenite growth kinetics during continuous heating experiments were made for two commercial low-alloy steels (C22 and C35). The observed growth behavior of individual austenite grains gives a valuable contribution to understanding the phase transformations on heating, i.e. austenite formation from ferrite and pearlite.

Microstrain Determination in Individual Grains of Laser Deposited Cladding Layers

The laser cladding technique makes the deposition of thick metallic, wear and corrosion resistant coatings feasible on weaker substrates. During the process, localized high thermal gradients generate internal stresses that may cause cracking when these overcome the fracture stress. To explain the formation and development of micro residual stresses the synchrotron 3DXRD microscopy technique was employed to investigate the strain tensor of individual grains of a Co based alloy cladding layer. The experimental method is based on the set of diffractions from a rotating specimen followed by indexing of reflections and identification of individual diffracting grains. The components of the strain tensor for these grains are calculated by a decomposition method applied to over-determined system of linear equations. The results of the individual strains tensor indicate modulation of the strains over neighboring grains. The final stress state depends on the solidification and cooling trajectory. Those groups of grains that solidify first are initially stress-free surrounded by molten material. The neighboring grains that solidify later will then assume the tensile character of the strain once the melt shrinks but limited by prior resolidified grains.

Phase transformations in steel studied by 3DXRD microscopy

The ferrite grain nucleation mechanism during the austenite/ferrite phase transformation is studied in situ in the bulk of three different steel grades by three-dimensional X-ray diffraction (3DXRD) microscopy. The main difference between the three steel grades is the carbon concentration. For each steel grade the ferrite fraction, nucleus density and nucleation rate are measured simultaneously during continuous cooling. By comparing the measured nucleation rate to the classical nucleation theory it is concluded that the activation energy for ferrite nucleation is about two orders of magnitude smaller than the current models predict for the three steel grades. During slow cooling the same nucleation behaviour is found for the three steel grades concerning the balance between the energy that is released by the elimination of interfaces and the energy that is required for the formation new interfaces during ferrite nucleation.

X-ray microscopy in four dimensions

Three-dimensional X-ray diffraction (3DXRD) microscopy offers the possibility of time-resolved mapping of structures down to the micrometer scale 1 , 2 , 3 , 4 , 5 , 6 , i.e. four-dimensional studies. In this review, the principles of the 3DXRD microscope are described and various examples of its applications are presented.

3DXRD microscopy for the study of solid-state phase transformation kinetics

In this paper the role of the 3DXRD microscope in understanding the underlying mechanisms of solid-state diffusional phase transformations is discussed.

Resolving Ambiguities in Reconstructed Grain Maps using Discrete Tomography

The so-called 3DXRD microscope, implemented at the European Synchrotron Radiation Facility in Grenoble, France, utilizes the principle of X-ray diffraction for mapping the crystalline grains within hard materials such as metals or ceramics. Present algorithms, using continuous models, roughly reconstruct the image from diffraction data, but they are often unable to assign unambiguous values to all pixels. We present an approach that resolves these ambiguous pixels by using a Monte Carlo technique that exploits the discrete nature of the problem and utilizes proven methods of discrete tomography. Based on simulations we show that most ambiguities can be successfully resolved.

In-Situ Measurements of Growth of Nuclei within the Bulk of Deformed Aluminium Single Crystals

With the 3DXRD microscope it is now possible to follow in-situ the 3D shape of a recrystallizing grain in the bulk of a deformed microstructure. This opens up the possibility of making direct measurements of boundary migration through a deformed matrix. This paper focuses on recrystalliztion in a deformed Aluminum single crystal with initial orientation (112)<111> (Cu).

3DXRD – Mapping Grains and Their Dynamics in 3 Dimensions

3-Dimensional X-Ray Diffraction (3DXRD) microscopy is a tool for fast and non-destructive characterization of the individual grains, sub-grains and domains inside bulk materials. The method is based on diffraction with highly penetrating hard x-rays, enabling 3D studies of millimeter - centimeter thick specimens. The position, volume, orientation, elastic and plastic strain can be derived for hundreds of grains simultaneously. Furthermore, by applying novel reconstruction methods 3D maps of the grain boundaries can be generated. With the present 3DXRD microscope set-up at the European Synchrotron Radiation Facility, the spatial resolution is ~ 5 µm, while grains of size 100 nm can be detected. 3DXRD microscopy enables, for the first time, dynamic studies of the individual grains and sub-grains within polycrystalline materials. The methodology is reviewed with emphasis on recent advances in grain mapping. Based on this a series of general 3DXRD approaches are identified for studies of nucleation and growth phenomena such as recovery, recrystallisation and grain growth in metals.

In Situ Investigation of Bulk Nucleation by X-Ray Diffraction

A new method for in-situ studies of nucleation in bulk metals based on high energy synchrotron radiation is presented. Copper samples cold rolled 20% are investigated. The crystallographic orientations near triple junctions are characterized using non-destructive 3DXRD microscopy before, during, and after annealing for 1 hour at 290°C. This method allows in-situ identification of new nuclei and the deformed material, which spawns the nuclei. Also, since data is acquired during annealing nucleation kinetics can be studied.

Three-Dimensional X-Ray Diffraction Microscopy Using High-Energy X-Rays

AbstractThree-dimensional x-ray diffraction (3DXRD) microscopy is a tool for fast and nondestructive characterization of the individual grains, subgrains, and domains inside bulk materials. The method is based on diffraction with very penetrating hard x-rays (E ≥ 50 keV), enabling 3D studies of millimeter-to-centimeter-thick specimens.The position, volume, orientation, and elastic and plastic strain can be derived for hundreds of grains simultaneously. Furthermore, by applying novel reconstruction methods, 3D maps of the grain boundaries can be generated. The 3DXRD microscope in use at the European Synchrotron Radiation Facility in Grenoble, France, has a spatial resolution of ∼5 μm and can detect grains as small as 150 nm. The technique enables, for the first time, dynamic studies of the individual grains within polycrystalline materials. In this article, some fundamental materials science applications of 3DXRD are reviewed: studies of nucleation and growth kinetics during recrystallization, recovery, and phase transformations, as well as studies of polycrystal deformation.

A method for in-situ measurements of the growth in the bulk of deformed single crystals at the 3DXRD microscope

AbstractWith the Three Dimensional X-ray Diffraction microscope (3DXRD) located at the European Synchrotron Radiation Facility (ESRF) full 3D spatial information of grains in the interior of a sample can be measured non-destructively. In this paper we discuss the possibility of an extension to this scenario, namely in-situ annealing studies, where the 3D spatial grain shape can be monitored as function of time. Consequently, local boundary migration rates can be estimated and compared to the deformed microstructure. Such information may reveal to what extend the deformed microstructure influences the growth of a grain during recrystallization.

Non-destructive mapping of grains in three dimensions

A 3D map of an interior grain and its crystallographic orientation in a single-phase bulk sample has been obtained non-destructively, for the first time, by 3DXRD microscopy using an algebraic reconstruction method. The method is new and has potentials for in situ 3D mapping of structural changes during for example annealing.