Using crystallographic symmetry in diffraction and contrast analysis

1989 ◽  
Vol 47 ◽  
pp. 504-505
Author(s):  
U. Dahmen ◽  
K.H. Westmacott
Keyword(s):  
Electron Microscopy ◽  
High Symmetry ◽  
Two Phase ◽  
Tem Analysis ◽  
Crystallographic Symmetry ◽  
The Matrix ◽  
Contrast Analysis ◽  
Practical Tool ◽  
Convergent Beam ◽  
Beam Diffraction

Despite the increased use of convergent beam diffraction, symmetry concepts in their more general form are not commonly applied as a practical tool in electron microscopy. Crystal symmetry provides an abundance of information that can be used to facilitate and improve the TEM analysis of crystalline solids. This paper draws attention to some aspects of symmetry that can be put to practical use in the analysis of structures and morphologies of two-phase materials.It has been shown that the symmetry of the matrix that relates different variants of a precipitate can be used to determine the axis of needle- or lath-shaped precipitates or the habit plane of plate-shaped precipitates. By tilting to a special high symmetry orientation of the matrix and by measuring angles between symmetry-related variants of the precipitate it is possible to find their habit from a single micrograph.

Micro-Milling Responses of Hierarchical Graphene Composites

2013 ◽  
Author(s):  
Bryan Chu ◽  
Johnson Samuel ◽  
Nikhil Koratkar
Keyword(s):  
Electron Microscopy ◽  
Surface Roughness ◽  
Tool Wear ◽  
Glass Fiber ◽  
Glass Fibers ◽  
Micro Milling ◽  
Two Phase ◽  
Graphene Composite ◽  
The Matrix ◽  
Phase Glass

The objective of this research is to examine the micro-machining responses of a hierarchical three-phase composite made up of micro-scale glass fibers that are held together by an epoxy matrix laden with nano-scale graphene platelets. To this end, micro-milling experiments are performed on both the hierarchical graphene composite as well as on a baseline two-phase glass fiber composite without the graphene additive. The composite microstructure is characterized using transmission electron microscopy and scanning electron microscopy methods. Tool wear, chip morphology, cutting force, surface roughness and delamination are employed as machinability measures. In general, the tool wear, cutting forces, surface roughness and extent of delamination are all seen to be lower for the hierarchical graphene composite. These improvements are attributed to the fact that graphene platelets improve the thermal conductivity of the matrix, provide lubrication at the tool-chip interface and also improve the interface strength between the glass fibers and the matrix. Thus, the addition of graphene to a conventional two-phase glass fiber epoxy composite is seen to not only improve its mechanical properties but also its machinability.

scholarly journals Microstructure and fracture mode of unalloyed dual phase austempered ductile iron

2021 ◽  
pp. 27-27
Author(s):  
Petar Janjatovic ◽  
Cekic Eric ◽  
Dragan Rajnovic ◽  
Sebastian Balos ◽  
Vencislav Grabulov ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Ductile Iron ◽  
Tensile Testing ◽  
Dual Phase ◽  
Material Microstructure ◽  
Two Phase ◽  
Major Disadvantage ◽  
The Matrix ◽  
Type Of Fracture ◽  
Scanning Electron

Dual phase ADI material microstructure consists of different amounts and morphologies of ausferrite and free ferrite, obtained by subjecting ductile iron to specific heat treatment. As such, its strength is lower compared to comparable ADI materials, but exhibiting a higher ductility, the major disadvantage of ADI. In the current study, an unalloyed ductile iron was intercritical austenitised in two-phase regions (?+?) at four temperatures from 840 to 780?C for 2 hours and austempered at 400?C for 1 hour to obtain dual phase ADI with different percentages of free ferrite and ausferrite. Metallographic and fracture studies were performed by light and scanning electron microscopy, respectively. Microscopy results were correlated to tensile testing results. The results indicated that, as the amount of ausferrite present in the matrix increases, higher values of strength and lower ductility are obtained. The fracture surfaces of dual phase ADI microstructures with 22.8% of ausferrite in their matrix have regions of quasi-cleavage fracture around last-to-freeze zones, related to the presence of ausferrite in those areas. The specimens with the highest values of ausferrite of 86.8% among the dual phase microstructure have a dominant quasi-cleavage type of fracture.

Micromilling Responses of Hierarchical Graphene Composites

2015 ◽  
Vol 137 (1) ◽  
Author(s):  
Bryan Chu ◽  
Johnson Samuel ◽  
Nikhil Koratkar
Keyword(s):  
Electron Microscopy ◽  
Surface Roughness ◽  
Tool Wear ◽  
Glass Fiber ◽  
Fiber Composite ◽  
Glass Fibers ◽  
Two Phase ◽  
Graphene Composite ◽  
The Matrix ◽  
Phase Glass

The objective of this research is to examine the micromachining responses of a hierarchical three-phase composite made up of microscale glass fibers that are held together by an epoxy matrix, laden with nanoscale graphene platelets (GPL). To this end, micromilling experiments are performed on both a hierarchical graphene composite as well as on a baseline two-phase glass fiber composite without the graphene additive. The composite microstructure is characterized using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) methods. Tool wear, chip morphology, cutting force, surface roughness, and fiber–matrix debonding are employed as machinability measures. In general, the tool wear, cutting forces, surface roughness, and extent of debonding are all seen to be lower for the hierarchical graphene composite. These improvements are attributed to the fact that GPL improve the thermal conductivity of the matrix, provide lubrication at the tool–chip interface, and also improve the interface strength between the glass fibers and the matrix. Thus, the addition of graphene to a conventional two-phase glass fiber epoxy composite is seen to improve not only its mechanical properties but also its machinability.

scholarly journals Formation mechanisms and atomic configurations of nitride phases at the interface of aluminum nitride and titanium

2008 ◽  
Vol 23 (8) ◽  
pp. 2221-2228 ◽  
Author(s):  
Chia-Hsiang Chiu ◽  
Chien-Cheng Lin
Keyword(s):  
Electron Microscopy ◽  
Aluminum Nitride ◽  
Analytical Electron Microscopy ◽  
Phase Region ◽  
Titanium Foil ◽  
Formation Mechanisms ◽  
Two Phase ◽  
Analytical Electron ◽  
The Matrix ◽  
Lamellar Layer

Aluminum nitride was bonded with a titanium foil at 1400 °C for up to 1 h in Ar. The AlN/Ti interfacial reactions were investigated using analytical electron microscopy. Reaction layers, consisting of δ-TiN, τ2-Ti2AlN, γ-TiAl, α2-Ti3Al, a two-phase region (α2-Ti3Al + α-Ti), and α-Ti (Al, N) solid solution, were observed after annealing at 1400 °C for 0.1 h. Among these phases, the α2-Ti3Al and (α2-Ti3Al + α-Ti) were formed during cooling. Further diffusion of N atoms into the reaction zone precipitates a chopped fiber-like α2-Ti2AlN in the matrix of γ-TiAl, with [110]γ−TiAl//[11¯20]τ2−Ti2AlN and (1¯1¯1)γ−TiAl//(1¯10¯3)τ2−Ti2AlN, by substituting N atoms for one-half Al atoms after annealing at 1400 °C for 1 h. The released Al atoms, due to the precipitation of τ2-Ti2AlN, resulted in an ordered Al-rich γ-TiAl or Ti3Al5. Furthermore, the α-Ti (Al, N) was nitridized into a lamellar layer (δ-TiN + α-Ti) with [110]δ−TiN//[11¯20]α−Ti and (111)δ−TiN//(0001)α−Ti.

Practical Examples of Point and Space Group Determination in Convergent Beam Diffraction

1980 ◽  
Vol 38 ◽  
pp. 188-191 ◽  
Author(s):  
J.W. Steeds ◽  
N.S. Evans
Keyword(s):  
Stacking Faults ◽  
Objective Lens ◽  
High Symmetry ◽  
Space Group ◽  
Thermal Disorder ◽  
Order Of Magnitude ◽  
Convergent Beam ◽  
Beam Diffraction ◽  
Unambiguous Assignment

The high quality of diffraction information generated by convergent beam electron microscopy provides many ways of arriving at an unambiguous assignment of a space group to a crystal under investigation. One method of space group determination involves tilting the crystal to a number of different zone axes and combining the information derived from each. However, it is often possible to obtain the same information more efficiently by concentrating on just one high symmetry zone axis and it is this approach which will be illustrated here. The prerequisites for the application of the technique are a good crystal and a microscope which offers a large angular view of the back focal plane of the objective lens. Specimen cooling is generally advantageous but has not been used in most of our work and, in particular, was not used for the results used as illustrations here. By the term 'good' crystal is meant a homogeneous and strain-free crystal without planar disorder (stacking faults, antiphase boundaries) linear disorder (dislocations) or point disorder. The requirements are certainly stringent but they need only operate over a cube of side approximately 1OO nm. Point disorder which produces an effect of the same order of magnitude as thermal disorder can be tolerated and strains less than 10-4are not detected. An angular view of 20° or so in the diffraction plane is generally acceptable although a larger view would be helpful for certain crystal structures and for low-specimen temperatures.

Electron microscopy of a Gd–Ba–Cu–O superconductor

1989 ◽  
Vol 4 (3) ◽  
pp. 515-520 ◽  
Author(s):  
R. Ramesh ◽  
G. Thomas ◽  
R. L. Meng ◽  
P. H. Hor ◽  
C. W. Chu
Keyword(s):  
Electron Microscopy ◽  
Microscopy Study ◽  
Annealed Sample ◽  
Electron Microscopy Study ◽  
Zone Axis ◽  
Matrix Phase ◽  
The Matrix ◽  
Tetragonal Form ◽  
Convergent Beam ◽  
Beam Patterns

An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd–Ba–Cu–O superconductor alloy. The GdBa2Cu3O7−x phase in the oxygen annealed sample is orthorhombic while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the [001] zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.

Surface zone-axis patterns

1984 ◽  
Vol 42 ◽  
pp. 516-517
Author(s):  
J. A. Eades ◽  
M. D. Shannon ◽  
M. E. Meichle
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Incident Beam ◽  
Zone Axis ◽  
Surface Zone ◽  
Transmission Electron ◽  
Beam Orientation ◽  
Convergent Beam ◽  
Beam Diffraction

In electron diffraction from crystals, whether it be in reflection or transmission, the intensity of the emergent beams varies in a complex way with the angle that the incident beam makes with the crystal structure. The techniques for displaying this variation of intensity as a function of incident beam orientation have mostly been applied to zone-axis orientations, where the variation is particularly elaborate. The resulting patterns, known as zone-axis patterns or zaps, have become an important part of transmission electron microscopy.There are several techniques for obtaining zaps. The best known is convergent-beam diffraction but they can also be obtained in the form of bend-contour patterns and Tanaka patterns, and by rocking methods.

The Microstructure of Electron-Beam Welds in Inconel 718

1980 ◽  
Vol 38 ◽  
pp. 332-333
Author(s):  
R. Vincent ◽  
J.W. Steeds
Keyword(s):  
Electron Beam ◽  
Cross Sections ◽  
Inconel 718 ◽  
Large Area ◽  
Edx Analysis ◽  
Preliminary Identification ◽  
The Matrix ◽  
Convergent Beam ◽  
Beam Diffraction ◽  
Convergent Beam Diffraction

Electron-beam welds in the Ni-base superalloy, Inconel 718 are freauently found to contain an extensive system of micro-cracks radiating from the weld boundary into the heat-affected zone (HAZ) of the matrix. To study precipitation in cross-sections of weld samples* over a large area adjacent to the weld, extraction replicas were prepared from the electro-polished and etched surfaces. Some preliminary identification of the extracted particles has been made by EDX analysis and convergent-beam diffraction, combined with scanning microscopy and EDX analysis of the electro-polished or ion-eroded surfaces. The welds are 1 cm deep, and near the top surface, where most of the long U+2018cracks’ occur (Fig.1a), the weld is 1.5 mm wide. The FAZ, as defined by a suitable etchant (10% HC1-methanol), extends for a further 1mm on each side. The grain size (50-100μm) is unchanged across the matrix-FAZ boundary. EDX spectra from the large precipitates (2-10μm) in the matrix and HAZ (Fig.la) show a strong Mb peak coupled with a weak Ti peak; the other alloy elements are entirely absent. Additional evidence from convergent-beam diffraction patterns (Fig.3) and measurement of the lattice constant2 (ao = 4.42 + 0.015 Å), proves that the majority of the particles are carbides, (Nb,Ti)C, with a F-centred cubic structure. These precipitates are absent from the weld, and the backbone of the dendritic weld precipitation is formed by thin, branched platelets (Fig.4). These are also carbides, (Nb,Ti)C, which recrystal 1ize from the melt. However, the FDX snectra now show weak additional peaks from most of the alloy elements (Ni, Cr, Fe, Mo).

scholarly journals Study on the Relationships between Microscopic Cross-Linked Network Structure and Properties of Cyanate Ester Self-Reinforced Composites

Polymers ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 950
Author(s):  
Hongtao Cao ◽  
Beijun Liu ◽  
Yiwen Ye ◽  
Yunfang Liu ◽  
Peng Li
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
The Self ◽  
Reinforced Composites ◽  
Two Phase ◽  
Reinforced Composite ◽  
Transmission Electron ◽  
The Matrix ◽  
Ft Ir ◽  
The Cross

Bisphenol A dicyanate (BADCy) resin microparticles were prepared by precipitation polymerization synthesis and were homogeneously dispersed in a BADCy prepolymer matrix to prepare a BADCy self-reinforced composites. The active functional groups of the BADCy resin microparticles were characterized by Fourier transform infrared (FT-IR) spectroscopy. The results of an FT-IR curve showed that the BADCy resin microparticles had a triazine ring functional group and also had an active reactive group -OCN, which can initiate a reaction with the matrix. The structure of the BADCy resin microparticles was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From the TEM results, the BADCy resin microparticles dispersed in the solvent were nano-sized and distributed at 40–60 nm. However, from the SEM results, agglomeration occurred after drying, the BADCy resin particels were micron-sized and distributed between 0.3 μm and 0.6 μm. The BADCy resin prepolymer was synthesized in our laboratory. A BADCy self-reinforced composite was prepared by using BADCy resin microparticles as a reinforcement phase. This corresponds to a composite in which the matrix and reinforcement phase are made from different morphologies of the same monomer. The DSC curve showed that the heat flow of the microparticles is different from the matrix during the curing reaction, this means the cured materials should be a microscopic two-phase structure. The added BADCy resin microparticles as reaction sites induced the formation of a more complete and regular cured polymer structure, optimizing the cross-linked network as well as increasing the interplay between the BADCy resin microparticles and prepolymer matrix. Relative to the neat BADCy resin material, the tensile strength, flexural strength, compressive strength and impact strength increased by 98.1%, 40.2%, 27.4%, and 85.4%, respectively. A particle toughening mechanism can be used to explain the improvement of toughness. The reduction in the dielectric constant showed that the cross-linked network of the self-reinforced composite was more symmetrical and less polar than the neat resin material, which supports the enhanced mechanical properties of the self-reinforced composite. In addition, the thermal behavior of the self-reinforced composite was characterized by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). The results of DMTA also establishes a basis for enhancing mechanical properties of the self-reinforced composite.

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