Focused Ion Beam Serial Sectioning Research Articles

Grain boundary energies in yttria‐stabilized zirconia

AbstractThe three‐dimensional microstructure of 8% yttria‐stabilized zirconia (YSZ) was measured by electron backscatter diffraction and focused ion beam serial sectioning. The relative grain boundary energies as a function of all five crystallographic grain boundary parameters were determined based on the assumption of thermodynamic equilibrium at the internal triple junctions. Grain boundaries with (100) orientations have low energies compared to boundaries of other orientations, and all [100] twist boundaries have relatively low energies. Other classes of boundaries with lower than average energies include [100] symmetric tilt boundaries with disorientations less than 40° and [111] twist boundaries with disorientations greater than 20°. At fixed misorientations, the relative areas of boundaries are inversely correlated to the relative grain boundary energy. The results suggest that texturing microstructures to increase the relative areas of [100] twist boundaries might increase the oxygen ion conductivity of YSZ ceramics.

Plasma Focused Ion Beam Serial Sectioning as a Technique to Characterize Nonmetallic Inclusions in Superelastic Nitinol Fine Wires.

Nonmetallic inclusion (NMI) populations in superelastic (SE) Nitinol fine wires (<140 μm in diameter) were investigated by combining plasma focused ion beam (PFIB) serial sectioning with scanning electron microscopy (SEM). High purity (HP)—lower oxygen content and standard purity (SP)—higher oxygen content Nitinol wires were sectioned and imaged. The three-dimensional (3D) reconstructions provided more complete connectivity of NMIs and pores as well as information about the distribution of the features within the wire volume that is not possible with traditional two-dimensional (2D) imaging techniques. NMIs were present alone and with pores in the leading and/or trailing edges of the inclusions, in addition to stringers (i.e., fractured, elongated NMI, and intermixed with pores adjacent to each other), all of which were parallel to the wire drawing axis. The area percentages for the NMIs were 0.01% (HP Nitinol) and 0.04% (SP Nitinol), while the volume percentages measured 0.09% (HP Nitinol) and 0.47% (SP Nitinol). The combined PFIB-SEM serial sectioning approach provided the requisite resolution necessary to distinguish between NMIs and pores at micron and submicron sizes. Information gathered from this technique can be used to better inform models and predictions for fatigue lifetimes based on statistical analyses of these feature populations.

Ellipsoidal mesoscale mineralization pattern in human cortical bone revealed in 3D by plasma focused ion beam serial sectioning

Visualizing bone mineralization and collagen fibril organization at intermediate scales between the nanometer and the hundreds of microns range, is still an important challenge. Similarly, visualizing cellular components which locally affect the tissue structure requires a precision of a few tens of nanometers at maximum while spanning several tens of micrometers. In the last decade, gallium focused ion beam (FIB) equipped with a scanning electron microscope (SEM) proved to be an extremely valuable structural tool to meet those ends. In this study, we assess the capability of a recent plasma FIB-SEM technology which provides a potential increase in measurement speed over gallium FIB-SEM, thus paving the way to larger volume analysis. Nanometer-scale layers of demineralized and mineralized unstained human femoral lamellar bone were sequentially sectioned over volumes of 6–16,000 μm3. Analysis of mineralized tissue revealed prolate ellipsoidal mineral clusters measuring approximately 1.1 µm in length by 700 nm at their maximum diameter. Those features, suggested by others in high resolution studies, appear here as a ubiquitous motif in mineralized lamellar bone over thousands of microns cubed, suggesting a heterogeneous and yet regular pattern of mineral deposition past the single collagen fibril level. This large scale view retained sufficient resolution to visualize the collagen fibrils while also partly visualizing the lacuno-canalicular network in three-dimensions. These findings are strong evidence for suitability of PFIB as a bone analysis tool and the need to revisit bone mineralization over multi-length scales with mineralized tissue.

Focused Ion Beam Serial Sectioning and 3D-Reconstruction of Nuclear Fuel

Focused Ion Beam Serial Sectioning and 3D-Reconstruction of Nuclear Fuel

High-throughput 3D reconstruction of stochastic heterogeneous microstructures in energy storage materials

Stochastic heterogeneous microstructures are widely applied in structural and functional materials, playing a crucial role in determining their performance. X-ray tomography and focused ion beam serial sectioning are frequently used methods to reconstruct three-dimensional (3D) microstructures, yet are demanding techniques and are resolution-limited. Here, a high-throughput multi-stage 3D reconstruction method via distance correlation functions is developed using a single representatively large-sized 2D micrograph for stochastic microstructures, and verified by X-ray micro-tomography datasets of isotropic and anisotropic solid oxide fuel cell electrodes. This method provides an economic, easy-to-use and high-throughput approach for reconstructing stochastic heterogeneous microstructures for energy conversion and storage devices, and can readily be extended to other materials.

Early Time Evolution of Selective Oxidation in a CMnSi AHSS

The influence of dew point temperature (DPT) and oxidation time on the selective oxidation of a Fe-0.09C-2.02Mn-0.91Si (wt pct) advanced high-strength steel during the early stages of oxidation was investigated in this study. Samples were annealed at 1123 K (850 °C) in a high-temperature confocal scanning laser microscope for 0, 30, 60, 90, and 120 seconds in an N2 + 5 pct H2 atmosphere with 243 K (− 30 °C) or 273 K (0 °C) DPT. Oxide morphology and chemistry were examined with respect to time and atmosphere DPT using scanning electron microscopy, scanning transmission electron microscopy, focused ion beam (FIB) milling, FIB serial sectioning, and energy dispersive spectroscopy techniques. Significant internal and external oxidation for all samples, including those with a 0 second isothermal hold, was observed. This indicated significant oxidation occurred upon heating. Samples oxidized in the 273 K (0 °C) DPT atmosphere exhibited intra- and intergranular internal oxidation and surfaces covered in discrete iron-rich nodules. These were attributed to stress generation during oxidation. Samples oxidized in the 243 K (− 30 °C) DPT atmosphere had shallow internal oxidation, sparse intragranular oxides, and surfaces rich in silicon and manganese containing oxide. Internal oxides for both atmospheres and all isothermal hold times were comprised of a silicon-rich core and manganese-rich outer shell was frequently observed. This core/shell structure was related to evolving oxide stability during the high-temperature exposure.

Solid/Self-Lubrication Mechanisms of an Additively Manufactured Ni–Ti–C Metal Matrix Composite

A Ni–TiC–C metal matrix composite (MMC) has been processed using laser engineered net shaping. This additive manufacturing technique produced a Ni–3Ti–20C (at.%) composition with in situ formation of homogeneously distributed eutectic and primary TiC and graphite precipitates throughout the Ni matrix. The MMC exhibits a low steady-state friction coefficient of ~0.1 in dry sliding conditions. Novel insights into solid/self-lubrication mechanisms, with implications to other metal matrix-graphite particle composites, were revealed with focused ion beam serial sectioning inside worn surfaces. It was determined that lowering of the friction coefficient was a result of the formation of a low interfacial shear strength disordered carbon tribofilm that extruded to the surface through refined Ni grain boundaries. This was supported by finite element analysis that showed the evolution of subsurface stress states and precipitate motion during repeated sliding frictional contact.

Silicon particle pinhole defects in aluminium\u2013silicon alloys

It was recently shown that silicon particles in heat-treated Al–Si casting alloys can contain flaws such as surface pinholes and grooves, which cause varying degrees of reduction in the in situ particle fracture strength and hence influence the mechanical properties of this class of alloys. In this work, we show that the formation of one class of such strength-limiting flaws in solidified and coarsened Si particles, namely surface pinholes, is caused by alloy impurities such as Fe and Ti in both binary eutectic Al–Si alloys and also in casting alloy A356. This is evidenced by using Focused Ion Beam serial sectioning tomography coupled with Energy-Dispersive X-Ray Spectroscopy, and confirmed by the observation that a high-purity Al–Si alloy presents a significantly lower proportion of pinholes along the surface of the silicon phase than does an alloy of commercial purity. A similar correlation between alloy purity and the formation of another, more severe strength-limiting particle defect, namely grooved interfaces, was on the other hand not found.

Three Dimensional Characterization of Tin Crystallography and Cu6Sn5 Intermetallics in Solder Joints by Multiscale Tomography

Decreasing pitch size in electronic packaging has resulted in a drastic decrease in solder volumes. The Sn grain crystallography and fraction of intermetallic compounds (IMCs) in small-scale solder joints evolve much differently at the smaller length scales. A cross-sectional study limits the morphological analysis of microstructural features to two dimensions. This study utilizes serial sectioning technique in conjunction with electron backscatter diffraction to investigate the crystallographic orientation of both Sn grains and Cu6Sn5 IMCs in Cu/Pure Sn/Cu solder joints in three dimensional (3D). Quantification of grain aspect ratio is affected by local cooling rate differences within the solder volume. Backscatter electron imaging and focused ion beam serial sectioning enabled the visualization of morphology of both nanosized Cu6Sn5 IMCs and the hollow hexagonal morphology type Cu6Sn5 IMCs in 3D. Quantification and visualization of microstructural features in 3D thus enable us to better understand the microstructure and deformation mechanics within these small scale solder joints.

Characterisation and quantification of cavities in 9Cr martensitic steel for power plants

This work focuses on the characterisation of cavities evolution in a P91 steel pipe in three conditions: as received, and after creep at 650°C and 60 MPa for 7000 and 9000 h. A field emission gun scanning electron microscope (FEG-SEM) equipped with focused ion beam (FIB) gun, a conventional scanning electron microscope (SEM) and a light optical microscope (LOM) have been employed for the investigation. This study reveals two types of cavities: the pre-existing cavities, which are rare in this type of heat resistant steels, with a mean diameter of 2·56 μm and the cavities produced during creep with diameters smaller than 0·6 μm. Lath boundaries and precipitates are found to be preferential sites for cavity nucleation. Furthermore, the number density and volume fraction of these small cavities are calculated from 2D measurements and compared to 3D results obtained by FIB serial sectioning.

Probing the mechanical properties and microstructure of WSi2/SixGe1−x multiphase thermoelectric material by nanoindentation, electron and focused ion beam microscopy methods

Thermoelectric (TE) materials such as silicon germanium (SiGe) alloys have been traditionally used in radioisotope thermoelectric generators (RTG) NASA applications. Beyond traditional RTG applications, we are exploring other applications in the energy harvesting arena. There is still a need to increment the TE figure of merit (ZT) of SiGe based TE alloys and we have been working on ways to improve it by incorporating tungsten di-silicide (WSi2) phases into the matrix by directional solidification (DS) process. Considerable efforts have been focused until now in microstructural engineering methods that lead to ZT improvement by microstructure optimization of TE materials. Although critical for the previous mentioned applications, work pertinent to the mechanical integrity of this type of WSi2/SiGe based TE materials is lacking. In this work, we explored for the first time the local mechanical properties and microstructure of WSi2/SixGe1−x multiphase thermoelectric material by nanoindentation, scanning electron microscopy (SEM), focused ion beam (FIB) and transmission electron microscopy (TEM) methods. We report hardness (H), modulus (E) and fracture toughness (kc) data for all phases. We obtained average H (and E) values (in GPa) of 12.94 (464.95) for the WSi2 phase, 19.49 (214.52) for the matrix, 14.95 (142.84) for the Si rich phase, and 13.98 (138.56) for the Ge rich phase respectively; while average kc values (in MPam0.5) were 1.37 for theWSi2, 0.52 for the matrix, 0.36 for the Si rich and 0.24 for the Ge rich phases respectively. FIB serial sectioning and cross-sectional TEM analysis is also included which provided insights on the deformation process below the nanoindentation area.

Multi-scale characterization by FIB-SEM/TEM/3DAP

In order to improve properties of functional materials, it is important to understand the relation between the structure and the properties since the structure has large effect to the properties. This can be done by using multi-scale microstructure analysis from macro-scale to nano and atomic scale. Scanning electron microscope (SEM) equipped with focused ion beam (FIB), transmission electron microscope (TEM) and 3D atom probe (3DAP) are complementary analysis tools making it possible to know the structure and the chemistry from micron to atomic resolution. SEM gives us overall microstructural and chemical information by various kinds of detectors such as secondary electron, backscattered electron, EDS and EBSD detectors. Also, it is possible to analyze 3D structure and chemistry via FIB serial sectioning. In addition, using TEM we can focus on desired region to get more complementary information from HRTEM/STEM/Lorentz images, SAED/NBD patterns and EDS/EELS to see the detail micro or nano-structure and chemistry. Especially, combination of probe Cs corrector and split EDS detectors with large detector size enable us to analyze the atomic scale elemental distribution. Furthermore, if the specimen has a complicated 3D nanostructure, or we need to analyze light elements such as hydrogen, lithium or boron, 3DAP can be used as the only technique which can visualize and analyze distribution of all constituent atoms of our materials within a few hundreds nm area. Hence, site-specific sample preparation using FIB/SEM is necessary to get desired information from region of interest. Therefore, this complementary analysis combination works very well to understand the detail of materials.In this presentation, we will show the analysis results obtained from some of functional materials by Carl Zeiss CrossBeam 1540EsB FIB/SEM, FEI Tecnai G(2) F30, Titan G2 80-200 TEMs and locally build laser assisted 3DAP. As the one of the example, result of multi-scale characterization for ultra-fine grain Nd-Fe-B permanent magnet will be shown [1]. In order to improve the magnetic properties, especially to increase the coercivity (resistance against magnetization reversal) of the magnet, decreasing the grain size and isolating each grain by non-ferromagnetic grain boundary phase are quite important since the nucleation of magnetic reversal from grain boundary phase can be suppressed and pinning force of magnetic domain wall at the grain boundary phase can be strengthened. Therefore, micro and nano structure and chemistry analysis can shed a light do grain boundary engineering.Figure1(a,b) shows SEM BSE images of ultrafine grain Nd-Fe-B sintered magnet and the reconstructed 3D tomography of Nd-rich phases obtained by FIB/SEM serial sectioning. This data can provide us information about the distribution of Nd-rich phase and its volume fraction. Moreover, the HRTEM image from the grain boundary phase, the 3DAP maps and the concentration depth profiles are shown in Fig.1(c,d,e). This magnet shows high coercivity (1517kA/m), and by comparing these results with the microstructures of low coercivity specimen, importance of grain boundary formation was confirmed and it gives us hint to improve the coercivity further. We will show the detail and results from other materials.jmicro;63/suppl_1/i6/DFU046F1F1DFU046F1Fig. 1.(a) SEM BSE images of ultrafine grain Nd-Fe-B sintered magnet. (b) 3D FIB/SEM tomography of Nd-rich phases. (c) HRTEM image from the grain boundary phase. (d) 3DAP maps of Nd, Cu and Al. (e) Concentration depth profiles for Fe, Nd+Pr, B, Co, Cu and Al, determined from the selected box in (d)[1].

Focused ion beam and scanning electron microscopy for 3D materials characterization

Abstract

The five-parameter grain boundary character and energy distributions of a fully austenitic high-manganese steel using three dimensional data

The three-dimensional interfacial grain boundary network in a fully austenitic high-manganese steel was studied as a function of all five macroscopic crystallographic parameters (i.e. lattice misorientation and grain boundary plane normal) using electron backscattering diffraction mapping in conjunction with focused ion beam serial sectioning. The relative grain boundary area and energy distributions were strongly influenced by both the grain boundary plane orientation and the lattice misorientation. Grain boundaries terminated by (111) plane orientations revealed relatively higher populations and lower energies compared with other boundaries. The most frequently observed grain boundaries were {111} symmetric twist boundaries with the Σ3 misorientation, which also had the lowest energy. On average, the relative areas of different grain boundary types were inversely correlated to their energies. A comparison between the current result and previously reported observations (e.g. high-purity Ni) revealed that polycrystals with the same atomic structure (e.g. face-centered cubic) have very similar grain boundary character and energy distributions.

Experimental measurement of surface strains and local lattice rotations combined with 3D microstructure reconstruction from deformed polycrystalline ensembles at the micro-scale

AbstractThis article describes a new approach to characterize the deformation response of polycrystalline metals using a combination of novel micro-scale experimental methodologies. An in-situ scanning electron microscope (SEM)-based tension testing system was used to deform micro-scale polycrystalline samples to modest and moderate plastic strains. These tests included measurement of the local displacement field with nm-scale resolution at the sample surface. After testing, focused ion beam serial sectioning experiments that incorporated electron backscatter diffraction mapping were performed to characterize both the internal 3D grain structure and local lattice rotations that developed within the deformed micro-scale test samples. This combination of experiments enables the local surface displacements and internal lattice rotations to be directly correlated with the underlying 3D polycrystalline microstructure, and such information can be used to validate and guide further development of modeling and simulation methods that predict the local plastic deformation response of polycrystalline ensembles.

The nano-scale anatomy of a complex carbon-lined microtube in volcanic glass from the ~ 92 Ma Troodos Ophiolite, Cyprus

Microtubular alteration textures in the glassy rims of pillow basalts and hyaloclastite may provide evidence of a sub-seafloor biosphere that has persisted since perhaps 3.5Ga. Reports of organic carbonaceous linings within such microtubes constitute one of the key lines of evidence for a biogenic origin. However, such linings have until now been studied mainly by low spatial resolution surface analysis techniques, resulting in a limited understanding of their origin.Here we analyze a large, complex microtube (Tubulohyalichnus annularis isp.) from the ~92Ma Troodos Ophiolite using focused ion beam milling combined with transmission electron microscopy (FIB-TEM), and focused ion beam serial sectioning combined with scanning electron microscopy (3D-FIB-SEM). These analyses reveal a distinct 50–200nm thick carbonaceous lining within the microtube. The lining is almost continuous and closely replicates the outer annulated morphology of the terminal end of the microtube. A spiral sub-structure previously seen using optical microscopy is also shown to be carbonaceous, comprising sheets that in places span the entire width of the microtube. Elemental mapping plus electron energy loss spectroscopy (EELS) shows that the carbon is organic and co-occurs with nitrogen. EELS and selected area electron diffraction (SAED) reveal that a clay mineral infills the remainder of the microtube, and this has a chemistry and structure consistent with the Fe-rich smectite, nontronite. Anti-correlation between carbon and the elements (Al, Ca, Fe, Mg, O, Si) in the infilling clay, plus the morphology of the carbon, show that the carbon lining is a discrete structure that predates clay mineral growth, thereby excluding the later absorption of organics onto the clay.This new data permits the rejection of a hydrothermal or metamorphic fluid derived origin for the carbonaceous linings to T. annularis isp., plus an origin from recent post-obduction groundwater hosted microorganisms. Our favored hypothesis is that the carbonaceous lining and sheet-like sub-structure were formed on the Cretaceous sub-seafloor by microbial activity in the volcanic glass. It is not yet possible however, to ascertain if the organic material comes from the putative microbe(s) that constructed the T. annularis isp. trace fossil, or from microbes that inhabited the pre-existing microtube. Further analysis of young in-situ oceanic crustal samples using these ultra-high-resolution FIB-TEM and 3D-FIB-SEM techniques may answer this critical outstanding question.

On the three-dimensional structure of WC grains in cemented carbides

In the present work, the size distribution and shape of WC grains in cemented carbides (WC–Co), with different Co contents, have been investigated in three dimensions. Direct three-dimensional (3-D) measurements, using focused ion beam serial sectioning and electron backscattered diffraction (EBSD), were performed and a 3-D microstructure was reconstructed. These measurements were supplemented by two-dimensional (2-D) EBSD and scanning electron microscopy on extracted WC grains. The data from 2-D EBSD collected on planar sections were transformed to three dimensions using a recently developed statistical method based on an iterative inverse Saltykov procedure. This stereological analysis revealed that the assumed spherical shape of WC grains during the Saltykov method is reasonable and the estimated 3-D size distribution is qualitatively in good agreement with the actual distribution measured from 3-D EBSD. Although the spherical assumption is generally fair, the WC grains have both faceted and rounded surfaces. This is a consequence of the relatively low amount of liquid phase during sintering, which makes impingements significant. Furthermore, the observed terraced surface structure of some WC grains suggests that 2-D nucleation is the chief coarsening mechanism to consider.

The relative grain boundary area and energy distributions in a ferritic steel determined from three-dimensional electron backscatter diffraction maps

The relative grain boundary area and energy distributions of a ferritic steel were characterized as a function of lattice misorientation and boundary plane orientation using focused ion beam serial sectioning combined with electron backscatter diffraction. The grain boundary energy and population depended on both the grain boundary plane orientation and lattice misorientation. When misorientation was ignored grain boundary planes with the (111) orientation had the minimum energy and the largest relative areas. The most commonly observed boundaries were {112} symmetric tilt boundaries with the Σ3 misorientation; this boundary also had a low energy. On average there was a strong inverse correlation between the relative areas of different types of grain boundaries and the relative grain boundary energies.

Effects of focused ion beam milling on electron backscatter diffraction patterns in strontium titanate and stabilized zirconia

This study investigates the effect of focused ion beam (FIB) current and accelerating voltage on electron backscatter diffraction pattern quality of yttria-stabilized zirconia (YSZ) and Nb-doped strontium titanate (STN) to optimize data quality and acquisition time for 3D-EBSD experiments by FIB serial sectioning. Band contrast and band slope were used to describe the pattern quality. The FIB probe currents investigated ranged from 100 to 5000 pA and the accelerating voltage was either 30 or 5 kV. The results show that 30 kV FIB milling induced a significant reduction of the pattern quality of STN samples compared to a mechanically polished surface but yielded a high pattern quality on YSZ. The difference between STN and YSZ pattern quality is thought to be caused by difference in the degree of ion damage as their backscatter coefficients and ion penetration depths are virtually identical. Reducing the FIB probe current from 5000 to 100 pA improved the pattern quality by 20% for STN but only showed a marginal improvement for YSZ. On STN, a conductive coating can help to improve the pattern quality and 5 kV polishing can lead to a 100% improvement of the pattern quality relatively to 30 kV FIB milling. For 3D-EBSD experiments of a material such as STN, it is recommended to combine a high kV FIB milling and low kV polishing for each slice in order to optimize the data quality and acquisition time.

Variations in Tantalum Carbide Microstructures with Changing Carbon Content

A wide variety of microstructures have been obtained by vacuum plasma spraying (VPS) 39Ta:61C atomic percent feedstock powders. During processing, the powder feed was fed through a high energy VPS plasma plume, where altering nozzle angle changed the overall retained carbon concentration in the deposited material. The samples were subsequently sintered and hot isostatic pressed to homogenize and consolidate the microstructure. The microstructures consisted of grains that were either equiaxed or acicular. In the samples with less carbon loss, the equiaxed grains were either the TaC phase or a TaC matrix that encased fine laths of Ta4C3. In the sample with the most carbon loss, acicular grains were found containing layered and parallel TaC, Ta2C, and Ta4C3 laths along the major‐axis of the grains. The phases of the compounds have been determined by using complimentary X‐ray diffraction and electron diffraction techniques. Focused ion beam serial sectioning and transmission electron microscopy tilt series tomography were performed to generate three‐dimensional reconstructions of the microstructure morphologies. This article addresses how tantalum carbide microstructures are controlled by the overall concentration and phase fraction content in each of these samples.