Selected Area Diffraction Analysis Research Articles

Characterization of chromium boride precipitates in the commercial superalloy GTD 111 after long-term exposure

During a study of the phase stability and decomposition behaviour of the commercial superalloy GTD 111 after many hours in service, it was noted that a lath or plate-like phase precipitated intragranularly. This phase was characterized using electron diffraction and energy dispersive spectroscopy. It was found to be heavily faulted, and consequently, may have been misidentified in previous studies. Due to the faulting, it was necessary to perform extensive selected area diffraction analyses in the transmission electron microscope in order to identify its structure. The analysis was complicated further by the fact that this structure is pseudo-hexagonal such that patterns from certain low and high symmetry zones appear almost identical; careful tilting experiments were used to reveal the structure as orthorhombic. Finally, some discussion of the implications of this particular microstructural feature on the mechanical properties of these alloys is provided based on rejuvenation heat treatments applied to these blades.

Orientation relationship between Nb and Nb5Si3 (D8l) phases in the eutectoid lamellar microstructure

The crystallography of a Nb/Nb5Si3 lamellar microstructure formed by Nb3Si decomposition has been investigated by transmission election microscopy. Upon solidification of a Nb–10 at.% Ti–20 at.% Si alloy, the high-temperature phase Nb3Si is retained at room temperature. During annealing at 1673 K, the Nb3Si phase transforms into the Nb and Nb5Si3 (D8l) phases with a lamellar microstructure through a eutectoid reaction. The orientation relationship between Nb and Nb5Si3 is determined by selected-area diffraction analyses as , and [133]Nb//[111]Nb5Si3. The present orientation relationship is explained by good atomic matching on the close-packed planes along the near close-packed directions.

Characteristics of Alumina Diffusion Barrier Films on Hastelloy

The diffusion behavior of elements constituting Hastelloy C-276 (C, Si, Mn, Co, W, Fe, Cr, Mo, and Ni) in alumina films was investigated using secondary ion mass spectroscopy. The films were deposited by ion-beam-assisted deposition and annealed in vacuum over a temperature range of 500–1000 °C. Characterization of film microstructure was performed using transmission electron microscopy and selected area diffraction analyses. The films were predominantly amorphous with alumina nanocrystallites nonuniformly dispersed throughout the volume both before and after annealing. A relatively wide interface region between the Hastelloy substrate and alumina film was formed in the as-deposited sample due to ion beam mixing. No diffusion of any of the substrate elements was observed after annealing, except for Mn, Cr, and Ni. The impurity depth distributions consisted of two components, which differed by several orders of magnitude with respect to diffusion coefficient and solubility. Activation energies and temperature dependencies of the diffusion coefficients were determined, and a diffusion mechanism was discussed.

An analysis of the microstructure and interfacial chemistry of steel–enamel interface

The microstructures of interface between the enamel and the hot-rolled steel pretreated with and without the NiO precoat has been investigated. The microstructure obtained in the sample with the NiO precoat consisted of an intricate network of Fe–Ni metallic rich phase dispersed in the matrix of a glassy phase, and a complex intergrowth inside large gaseous bubbles. Transmission electron microscopy examinations revealed that the large metallic Fe–Ni-rich phase consisted of the colonies of crystals containing spinel NiFe 2O 4, whereas the intergrowth were composed of nanocrystalline FeO and metallic (Fe,Ni) particles with a large concentration of carbon in the form of a graphite film. In samples without the NiO precoat, there was a complete absence of large dispersed metallic phase and large bubbles at the interface. Moreover, the presence of an oxide layer on the surface of the steel pretreated with the NiO precoat was identified by the selected-area diffraction analysis. In the absence of NiO precoat, however, only individual oxide particles were observed. Based on the experimental evidences and thermodynamic analysis of reactions at the interface, the investigation explains the reasons for an extensive dispersion of the metallic Fe–Ni-rich metallic particulates and the large bubbles encapsulating oxide and metallic phases. These differences in microstructure, especially carbon precipitation, account for the role of NiO in reducing the fish-scaling tendency.

High-resolution investigation of atomic interdiffusion during Co/Ni/Si phase transition

We studied the phase transition of Co/Ni thin films on amorphous silicon using an approach based on in situ sheet resistance analyses during isothermal annealing processes. Compared to conventional Co/Si systems, Co/Ni/Si reaction produces a double peak in the resistance curve versus time. This behavior has been extensively studied by Rutherford backscattering spectroscopy, x-ray diffraction, energy filtered transmission electron microscopy, and selected area diffraction analyses. It has been found that the kinetic evolution of the Co/Ni/Si structure occurs through two consecutive transition stages which are strictly related to each of the resistance peaks. At the beginning, cobalt atoms remain confined at the surface while nickel reacts with silicon hence producing the occurrence of the first resistance peak. The second peak is instead related to the cobalt atoms diffusing through the grain boundaries of the underlying Ni2Si layer, converting Ni2Si in a continuos CoSi film and forming pipelines through the underlying NiSi down the substrate. As a result, a ternary compound nucleates in contact with silicon. The final structure at the plateau of the resistance curve is a multilayer of CoSi/NiSi/Co(Ni)Si2, different from the case of Co/Ni thick-layer reaction.

Assessment of asbestos burden in the placenta and tissue digests of stillborn infants in South Texas.

The primary aim of this prospective study was to examine the tissues and placentas of autopsied stillborn infants for presence of asbestos fibers. Asbestos burden of lung, liver, skeletal muscle, and placenta digests of 82 stillborn infants was determined using standard bleach digestion technique. The digests were examined by electron microscopy, and the types of fibers determined using energy dispersive x-ray analysis and selected area diffraction analysis. Digests of 45 placentas collected from deliveries of liveborn healthy infants were processed and examined similarly as controls. Asbestos fibers were detected in 50% of the fetal digests and 23% of the placental digests of stillborn infants. Of the fibers present, 88% were chrysotile, 10% were tremolite, and 2% were actinolite and anthophyllite. Fibers measured 0.5-16.73 microgram in length (mean 1.55 microgram), and 0.03-0.8 microgram in width (mean 0.098 microgram). Lungs were most frequently positive for fibers (50%), followed by muscle (37%), placenta (23%), and liver (23%). Mean fiber counts were highest in the liver (58,736 f/g), followed by placenta (52,894 f/g), lungs (39,341 f/g), and skeletal muscle (31,733 f/g). Digests of 15% of the control placentas also showed asbestos fibers, although in very small numbers. The mean fiber count of the stillborn placentas (52,894 f/g) was significantly higher than the mean fiber count of the control placentas (mean 19 f/g) (p = 0.001). A highly significant association was found between fiber presence in stillborns and a maternal history of previous abortions (p = 0.007). A significant association was also found between fiber presence and placental diseases (p = 0.041). An association was suggested between working mothers and fiber presence (p = 0.19), although it did not reach statistical significance. The study documents the presence of small and thin asbestos fibers in stillborn fetal tissues and placenta. Significantly higher number of fibers were found in stillborn tissues compared to controls (liveborn placenta). The absence of a maternal history of asbestos-related occupations suggests that the fibers may have been acquired through environmental exposure.

Heteroepitaxial nucleation of diamond on nickel

Highly oriented diamond has been grown on (100) nickel substrates by the hot filament chemical vapor deposition method. Epitaxial nuclei were obtained by a diamond powder seeding and high temperature annealing process. Since the timing of the process was crucial for the achievement of a high degree of orientation and high density of diamond nuclei, a real-time, in-situ laser reflectometry system was developed to monitor changes in surface morphology observed during the high temperature annealing stage. Characteristic features observed in the intensities of reflected and scattered light were interpreted by comparison with scanning electron micrographs of the samples quenched at sequential stages of the process. It was concluded that the scattered light signal can be effectively used as a process steering parameter. Using this technique, oriented nucleation and growth of diamond on Ni was reproducibly achieved. Auger spectroscopy showed that up to 6 at% of carbon was dissolved in the nickel surface layer. The investigation of interfacial microstructures and phases involved by transmission electron microscopy revealed the formation of Ni4C already in the early stages of nucleation. This phase was manifested as coherent precipitates and is believed to have been the precursor for diamond nucleation. Perfectly epitaxial diamond was grown by this process. The epitaxial relationship was determined by cross-sectional transmission electron microscopy and selected area diffraction analysis.

Is there transplacental transfer of asbestos? A study of 40 stillborn infants.

An autopsy study was conducted to investigate whether there is transplacental transfer of asbestos in humans. The asbestos burden of lung, liver, skeletal muscle, and placenta digests of 40 stillborn infants was determined using a bleach digestion method. The fibers detected in the tissue digests were characterized as to the type of asbestos, using electron microscopy, energy-dispersive x-ray analysis, and selected-area diffraction analysis. Placental digests of 45 full-term, liveborn infants were similarly processed as controls. Low levels of small, thin, uncoated asbestos fibers were detected in the placentas and organs of 37.5% of the stillborn infants (15 of 40). The fiber sizes ranged from 0.05 to 5.0 microns in length and 0.03 to 0.3 micron in width, with a mean length of 1.15 microns and a mean width of 0.069 micron. Maximum numbers of fibers were found in the lungs (mean 235,400 fibers/g; n = 10), followed by liver (mean 212,833 fibers/g; n = 6), placenta (mean 164,500 fibers/g; n = 4), and skeletal muscle (80,000 fibers/g; n = 1). The fibers were detected at all stages of gestation and showed no association with gestational age. A significant association was found between fiber presence and working mothers, and positive but nonsignificant associations were found with maternal history of drug abuse, previous abortions, and fetal maceration. No association was found between premature rupture of membranes and fiber presence. No fibers were detected in the 45 placentas of the liveborn control infants. There was a highly significant difference in the asbestos fiber counts of the placentas of the stillborn and liveborn infants (P < .001). Our studies demonstrate the presence of short and thin asbestos fibers in stillborn infants and their positive association with working mothers.

Boride morphology in A (Fe, V, B) Ti-alloy containing B2-phase

The morphology of borides grown from the melt in a Ti-Al (Fe, V, B) alloy has been investigated. Flake-like dispersoids are shown by energy dispersive X-ray spectroscopy and electron energy loss boron maps to consist of interleaved titanium boride and B2 grains, with selected area diffraction analysis identifying the boride phase as TiB2. High resolution electron microscopy reveals that the TiB2 and B2 are very high aspect ratio plates, reflecting the overall morphology of the dispersoids, with the interfacial and orientational relationship being {1010}TiB2 // {001}B2 and <0001=TiB2 // <010=B2. Growth methods of the TiB2/B2 dispersoids are discussed in light of the surprisingly fine nano-scale of the interleaving plates.

Microstructural Investigation of the Early External Callus after Diaphyseal Fractures of Human Long Bone

Microstructures of the early external callus after diaphyseal fractures of human long bone were investigated by using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. It was found that the main structural framework of the human early callus consists of disordered, mineralized collagen fibrils with a small fraction of regions of ordered collagen fibrils. X-ray diffraction analyses show that hydroxyapatite containing some carbonate impurity has been the dominant crystalline phase in the human early callus. In addition, a small amount of brushite phase was detected. Selected area diffraction analyses indicated that hydroxyapatite microcrystals were embedded in microfibrils with a diameter of 4.5 nm and well-banded fibrils, whereas brushite particles of 15-20 nm in an irregular shape were located in the noncollagenous organic matter around the nonmineralized, ordered collagen fibrils. The spatial distribution of the brushite particles in the human early callus was for the first time determined. The brushite particles probably serve as the reservoir of calcium and phosphate ions for subsequent mineralized periods rather than the precursor of hydroxyapatite.

Study of Ni/Ni3Al diffusion-couple interface by AEM and HREM

The interface between the Ni-rich solid solution phase (γ phase) and the intermetallic phase (γ'phase) with the Ll2-ordered Ni3Al structure plays an important role in the strengthening of Ni-based two-phase alloys such as superalloys. In this study, we have examined microstructure and diffusional phenomena across the ϒ/ϒ' interface by analytical electron microscopy (AEM) and high resolution electron microscopy (HREM).Fully annealed high-purity Ni (99.9%) was coupled with Ni-25mol%Al and subjected to diffusion anneal at temperatures of 1073 and 1173K. Thin specimens were prepared from these diffusion couples by careful cutting, grinding, electro-polishing and ion-milling, details of which are described elsewhere. We used three different types of electron microscopes: (a) JEM-2000FX (at 200kV) for measurements of the overall concentration gradient with a probe size of ∼20nm, microstructure observations and selected area diffraction analyses, (b) EM400T-FEG (at 100kV) for high spatial resolution micro-chemical analysis with a probe size of ∼3nm, and (c) JEM-4000EX (at 400kV) for observations of lattice images at the interface. Characteristic x-ray lines of Ni Kα, Al Kα, and Ni La were measured by energy dispersive x-ray spectrometers with a Be-type window which were attached on both JEM-2000FX and EM400T-FEG. Ni Kα and Al Kα lines were used for the determination of compositions, and Ni Kα and Ni Lα lines were for the determination of local thicknesses. X-ray absorption corrections were made by the differential x-ray absorption (DXA) method when determining concentration gradients and by the extrapolation method when determining k-factors.

Asbestos in organs and placenta of five stillborn infants suggests transplacental transfer

Digests of lungs, liver, and placenta from five stillborn infants of 22 to 38 weeks gestational age were examined for asbestos and other fibers using light and electron microscopy, energy dispersive X-ray analysis, and selected area diffraction analysis. Uncoated chrysotile asbestos fibers were found in the digests of at least one of the three tissues examined from each stillborn infant. The asbestos fiber burdens ranged from 71,000 to 357,000 fibers/g wet tissue. Most of the fibers were small, with the mean length ranging from 0.83 to 2.53 microns. While appreciable numbers of uncoated chrysotile fibers were present, no coated asbestos fibers were found in any of the stillborns. Both coated and uncoated nonasbestos fibers were found in at least one of the tissue digests of all five stillborns. The uncoated nonasbestos fibers were characterized as aluminum silicates, diatomaceous earth fragments, or other fibers. The coated nonasbestos fibers or ferruginous bodies were consistent with being formed on diatomaceous earth fragments, black carbon cores, or sheet silicate cores. Since the placenta is the only route of communication between the fetus and the outside environment, our findings strongly suggest a transplacental transfer of asbestos and other fibers in humans.

The Microstructure of ZrN/GaAs Schottky Contacts and its Correlation with Electrical Properties.

ABSTRACTThe self-aligned GaAs metal-semiconductor field-effect transistor technology requires that the gate material maintains a good rectifying contact with the GaAs substrate when subjected to high-temperature annealing around 800–900° C. ZrN Schottky contacts to GaAs were previously shown to have excellent electrical properties at high tempratures. An increase of barrier height and a decrease in the reverse breakdown voltage with rapid thermal annealing at temperatures up to 900° C has been observed. The ideality factor increases after rapid thermal annealing at 900° C.In an attempt to explain the above observations, we investigated the interface structure of such contacts under as-deposited and annealed conditions. By high resolution TEM it was found that the interface of as-deposited samples is fairly flat but protrusions form after rapid thermal annealing treatment at 850 and 900° C. The selected area diffraction analysis shows the presence of ZrO2 near the interface.It is therefore likely that protrusions are the cause of the degradation of electrical properties of the contacts. These protrusions may be caused by the presence of a residual oxide layer before deposition. Indeed, a deposition of ZrN after sputter cleaning the substrates before deposition procedure resulted in an abrupt interface even after annealing at 900° C.

Post-implantation heat treatment of nitrogen-implanted 440C stainless steel

Post-implantation heat treatment was performed on nitrogen implanted 440C stainless steel for varying times and temperatures. The results show surface microhardness may be increased by thermal aging treatments similar to that of age hardening alloys. The increases in surface hardness can be attributed to the formation of nitride precipitates in the matrix during the aging heat treatment. Transmission electron microscopy and selected area diffraction analyses demonstrated some preliminary nitride formation following implantation and aging. The principal nitride found was CrN. The matrix of the as-received 440C stainless steel was found to have a b.c.t. martensitic structure with a high dislocation-tangle density.

Characterization of hard nitride and carbide titanium and zirconium coatings on high‐speed steel cutting tool inserts

Hard nitride and carbide coatings of titanium and zirconium deposited by reactive evaporation and reactive sputtering techniques were characterized by electron microscopy and Auger spectroscopy to determine the effect of coating process on coating composition and microstructure. Analysis of the chemical composition by Auger spectroscopy revealed the coatings were of high purity with slight differences in stoichiometry depending on the coating technique. Both techniques produced coatings with a columnar microstructure. However, the reactive sputtering technique produced coarser (shorter and wider) columnar grains than the reactive evaporation technique. Furthermore, selected area diffraction analysis of reactively sputtered ZrN coatings showed a two‐phased zone (hcp Zr and fcc ZrN) near the substrate/coating interface, while TiC coatings deposited by reactive sputtering and evaporation only showed a single‐phase region of fcc TiC.

Metastable phase formation in rapidly solidified submicron powders of Al-30.3at.%Ge eutectic alloy

Submicron powders of an Al-30.3at.%Ge (eutectic) alloy produced by electrohydrodynamic atomization have been melted and rapidly solidified in a transmission electron microscope. A metastable phase, previously unreported in the literature, has been identified. Selected area diffraction analysis was used to determine the structure of this phase, which was found to be hexagonal (space group, P6/mmm) with a ≈ 1.42 nm and c ≈ 0.74 nm.

Tem Study Of Amorphous Alloys Produced By Ion Implantation

SUMMARYIon implantation is a technique for introducing foreign elements into surface layers of solids. Ions, as a suitably accelerated beam penetrate the surface, slow down by collisions with target atoms to produce a doped layer. This non‐equilibrium technique can provide a wide range of alloys without the restrictions imposed by equilibrium phase diagrams.This paper reports on the production of some amorphous transition metal‐metalloid alloys by implantation. Thinned foils of Ni, Fe and stainless steel were implanted at room temperature with Dy+ and P+ ions at doses between 1018 and 1021 ions m−2 at energies of 20 and 40 keV respectively. Transmission electron microscopy and selected area diffraction analysis were used to investigate the implanted specimens.Radial diffracted intensity measurements confirmed the presence of an amorphous implanted layer. The peak positions of the maxima are in good agreement with data for similar alloys produced by conventional techniques. Only certain ion/target combinations produce these amorphous layers. Implantations at doses lower than those needed for amorphization often result in formation of new crystalline phases such as an h.c.p. phase in nickel and a b.c.c. phase in stainless steel.

Salpeter-induced dermal changes electron-microscopically indistinguishable from pseudoxanthoma elasticum

Salpeter-induced calcium deposits in ten patients showed a close clinical and histopathological similarity to the lesions of pseudoxanthoma elasticum. By electron microscopy and selected area diffraction analyses of the calcium deposits we find the changes indistinguishable from the changes previously described in involved skin of patients suffering from PXE. Clinically our patients were compared with the fourteen patients with traumatic calcification previously described.

The morphology and substructure of martensite in maraging steels

Thin foil transmission electron microscopy, X-ray diffraction and dilatometric techniques have been used to study the martensitic γ → α transformation in three steels with nominal contents of 8 pct nickel and 0.2 pct beryllium and chromium contents of 12, 14 and 16 pct. In each case the martensite formed as laths with a habit plane close to {225}γ. With increasing chromium content and increasing cooling rate greater numbers of the laths were observed to be internally twinned. Detailed analysis of the martensitic transformation suggested that the internally twinned laths are formed by a sequence of γ→ e or faulted γ→ ά. The orientation relationships between the three phases γ, e and α, determined from selected area diffraction analysis, corresponded to Kurdjumov-Sachs.

The Effect of Hydrogen Reduction on the Morphology of Copper Oxide Whiskers

A series of closely controlled experiments was conducted to determine the effect of hydrogen reduction on the morphology of oxide whiskers formed on unannealed and preannealed copper. Initial reduction occurred along random sites at the whisker surface. No preferential reduction at the whisker tip was observed. During the reduction cycle, the whiskers collapsed to form small irregularly shaped high‐opacity nodes. Some differences were observed in the rate and manner in which the whiskers reduced on the unannealed and preannealed samples which were attributed to initial variations in size and shape of the whiskers. Selected area diffraction analyses of the reduced products revealed that the whiskers changed from to and then to Cu. appeared to form adjacent to the metal surface.Replica examinations of the oxidized‐reduced surfaces when compared with replicas of the original surface revealed considerable surface rearrangement with the formation of subgrain‐type structure. The size of the subgrains formed on the preannealed sample appeared to be smaller than that obtained on the unannealed sample. In most cases, the reduced oxide whisker growth products appeared to emanate from subgrain boundary intersections rather than from subboundary interiors.