Decomposition of Quasicrystalline Phase in a Rapidly Solidified Ai-Fe-V-Si Alloy

1990 ◽  
Vol 186 ◽  
Author(s):  
W. J. Park ◽  
S. Ahn ◽  
N.J. Kim
Keyword(s):  
Icosahedral Phase ◽  
Quasicrystalline Phase ◽  
Silicide Phase ◽  
In Situ Tem ◽  
Matrix Interface ◽  
Melt Spun ◽  
Wheel Side ◽  
Rapidly Solidified ◽  
Cast Microstructure

AbstractDecomposition of quasicrystalline phase formed in a rapidly solidified Al-Fe-V-Si alloy has been studied by TEM. The as-cast microstructure varies through the thickness of melt-spun ribbon; microeutectic precipitation of the bcc silicide near the wheel side, formation of globular quasicrystalline icosahedral phase with the microeutectic silicide phase at the middle of the ribbon, and the decomposition of quasicrystalline phase near the air side of the ribbon. During heating, as observed by annealing studies and by in-situ TEM studies, quasicrystalline phase decomposes into various phases such as aluminum, silicide and other unidentified phases. It has been shown that the preferential sites for the transformation are either at the center of quasicrystalline particles or at the quasicrystal/matrix interface, depending on the location of quasicrystalline particles.

Microstructural Variations in Melt-Spun Rapidly Solidified Ribbons

1985 ◽  
Vol 43 ◽  
pp. 54-55
Author(s):  
L. A. Bendersky ◽  
W. J. Boettinger
Keyword(s):  
Solid State ◽  
Processing Parameters ◽  
Heat Extraction ◽  
Solid State Reactions ◽  
Careful Examination ◽  
Ion Milling ◽  
Melt Spun ◽  
Wheel Side ◽  
Rapidly Solidified ◽  
Heat Extraction Rate

Rapid solidification produces a wide variety of sub-micron scale microstructure. Generally, the microstructure depends on the imposed melt undercooling and heat extraction rate. The microstructure can vary strongly not only due to processing parameters changes but also during the process itself, as a result of recalescence. Hence, careful examination of different locations in rapidly solidified products should be performed. Additionally, post-solidification solid-state reactions can alter the microstructure.The objective of the present work is to demonstrate the strong microstructural changes in different regions of melt-spun ribbon for three different alloys. The locations of the analyzed structures were near the wheel side (W) and near the center (C) of the ribbons. The TEM specimens were prepared by selective electropolishing or ion milling.

Microstructural characterization of rapidly solidified Al–Fe–Si, Al–V–Si, and Al–Fe–V–Si alloys

2001 ◽  
Vol 16 (7) ◽  
pp. 2103-2117 ◽  
Author(s):  
A. K. Srivastava ◽  
S. Ranganathan
Keyword(s):  
Elevated Temperatures ◽  
Microstructural Characterization ◽  
Icosahedral Phase ◽  
Silicide Phase ◽  
Icosahedral Quasicrystal ◽  
Icosahedral Symmetry ◽  
Scanning Calorimetry ◽  
Lower Temperature ◽  
Rapidly Solidified ◽  
Microscopy Techniques

The present study of rapidly solidified melt-spun Al80Fe14Si6 Al80V14Si6, and Al80Fe10V4Si6 alloys by electron microscopy techniques, x-ray diffractometry, and differential scanning calorimetry leads to a number of microstructural results. Coexistence of a micro-quasicrystalline state of an icosahedral phase with monoclinic θ–Al13Fe4 and hexagonal β–Al6V in Al–Fe–Si and Al–V–Si alloys, respectively, is reported. Also, the growth morphology of the icosahedral phase surrounded by a crystalline ring was investigated in an Al–Fe–V–Si alloy. The crystalline ring has the particles of the cubic α–Al12(Fe,V)3Si silicide phase. Evidence of irrational twinning of cubic crystals, giving rise to a symmetry not deviating much from icosahedral symmetry was found in this alloy. In all the three alloys crystalline intermetallics were elucidated in the context of rational approximants of an icosahedral quasicrystal. It was noticed that while the icosahedral phase in Al–Fe–Si and Al–V–Si alloys transforms to crystalline intermetallics at about the same temperature (approximately 610 K), the transformation of icosahedral phase in Al–Fe–V–Si alloy occurred at a relatively lower temperature (540 K). The origin of different metastable microstructures and their stability at elevated temperatures, in these alloys, are compared and discussed.

Micromechanisms of Deformation and Fracture in Rapidly Solidified Ni3Al Alloys

1990 ◽  
Vol 213 ◽  
Author(s):  
G. Liu ◽  
G.M. Bond
Keyword(s):  
Dislocation Motion ◽  
In Situ Tem ◽  
Intermetallic Alloys ◽  
Stress Concentrations ◽  
X Ray ◽  
Deformation And Fracture ◽  
The Subject ◽  
Rapidly Solidified ◽  
Degree Of Order

ABSTRACTRapidly solidified Ni76 Al24 ribbons, with and without boron, have been the subject of in-situ TEM deformation studies, as well as X-ray and TEM characterization and TEM fractography. The aim has been to gain a better understanding of the influence of a reduced degree of order on grainboundary behavior and ductility. This, in turn, allows fresh insights to be gained, both into the manner in which boron additions can enhance ductility, and into the potential usefulness of sequential ordering in intermetallic alloys with a tendency to intergranular failure. Lower degrees of order are found to reduce stress concentrations at grain boundaries; this effect is due to easier generation of dislocations from boundary sources, and, to a lesser extent, the braking action of thermal APB's on dislocation motion. The beneficial effect of boron on ductility is seen to result, at least in part, from enhanced boundary cohesive strength.

Polytypism in a decagonal quasicrystalline Al–Co phase

1989 ◽  
Vol 22 (2) ◽  
pp. 96-99 ◽  
Author(s):  
J. Menon ◽  
C. Suryanarayana ◽  
G. Singh
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
Quasicrystalline Phase ◽  
Phase Variations ◽  
Diffraction Patterns ◽  
Rapidly Solidified

A decagonal quasicrystalline phase has been produced in rapidly solidified binary Al–14 to 25 at.% Co and ternary Al–20 at.% Co–5 at.% Si alloys. Observation of periodicity along one of the directions in the electron diffraction patterns has confirmed the decagonal nature of the phase. Variations in periodicity ranging from 4 to 16 Å suggest that a polytypism-like phenomenon occurs in these phases. By in situ hot-stage electron microscopy, it can be shown that one polytype transforms into another. Reasons for the formation and transformation of polytypes in decagonal quasicrystalline phases are discussed.

In situ TEM studies of irradiation effects for materials improvement

1991 ◽  
Vol 49 ◽  
pp. 452-453
Author(s):  
Charles W. Allen
Keyword(s):  
Nuclear Reactor ◽  
Austenitic Stainless Steels ◽  
High Energy ◽  
Point Of View ◽  
In Situ Tem ◽  
Irradiation Effects ◽  
Tem Analysis ◽  
Radiation Induced ◽  
Analytical Tools

Irradiation effects studies employing TEMs as analytical tools have been conducted for almost as many years as materials people have done TEM, motivated largely by materials needs for nuclear reactor development. Such studies have focussed on the behavior both of nuclear fuels and of materials for other reactor components which are subjected to radiation-induced degradation. Especially in the 1950s and 60s, post-irradiation TEM analysis may have been coupled to in situ (in reactor or in pile) experiments (e.g., irradiation-induced creep experiments of austenitic stainless steels). Although necessary from a technological point of view, such experiments are difficult to instrument (measure strain dynamically, e.g.) and control (temperature, e.g.) and require months or even years to perform in a nuclear reactor or in a spallation neutron source. Consequently, methods were sought for simulation of neutroninduced radiation damage of materials, the simulations employing other forms of radiation; in the case of metals and alloys, high energy electrons and high energy ions.

Spherulite Structures in a Melt Spun Fe-Ni Austenitic Steel

1985 ◽  
Vol 43 ◽  
pp. 52-53
Author(s):  
G. M. Michal ◽  
T. K. Glasgow ◽  
T. J. Moore
Keyword(s):  
Austenitic Steel ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Large Range ◽  
Amorphous Structure ◽  
Nucleation And Growth ◽  
Ni Alloys ◽  
Melt Spun ◽  
Crystal Fibers ◽  
Rapidly Solidified

Large additions of B to Fe-Ni alloys can lead to the formation of an amorphous structure, if the alloy is rapidly cooled from the liquid state to room temperature. Isothermal aging of such structures at elevated temperatures causes crystallization to occur. Commonly such crystallization pro ceeds by the nucleation and growth of spherulites which are spherical crystalline bodies of radiating crystal fibers. Spherulite features were found in the present study in a rapidly solidified alloy that was fully crysstalline as-cast. This alloy was part of a program to develop an austenitic steel for elevated temperature applications by strengthening it with TiB2. The alloy contained a relatively large percentage of B, not to induce an amorphous structure, but only as a consequence of trying to obtain a large volume fracture of TiB2 in the completely processed alloy. The observation of spherulitic features in this alloy is described herein. Utilization of the large range of useful magnifications obtainable in a modern TEM, when a suitably thinned foil is available, was a key element in this analysis.

In situ TEM measurements of the electrical properties of interface dislocations

1992 ◽  
Vol 50 (2) ◽  
pp. 1338-1339
Author(s):  
F. M. Ross ◽  
R. Hull ◽  
D. Bahnck ◽  
J. C. Bean ◽  
L. J. Peticolas ◽  
...  
Keyword(s):  
Electrical Properties ◽  
Electronic Device ◽  
In Situ Tem ◽  
Device Performance ◽  
Misfit Dislocations ◽  
Electrical Characteristics ◽  
Strained Layer ◽  
Transmission Electron ◽  
Interfacial Dislocations

We describe an investigation of the electrical properties of interfacial dislocations in strained layer heterostructures. We have been measuring both the structural and electrical characteristics of strained layer p-n junction diodes simultaneously in a transmission electron microscope, enabling us to correlate changes in the electrical characteristics of a device with the formation of dislocations.The presence of dislocations within an electronic device is known to degrade the device performance. This degradation is of increasing significance in the design and processing of novel strained layer devices which may require layer thicknesses above the critical thickness (hc), where it is energetically favourable for the layers to relax by the formation of misfit dislocations at the strained interfaces. In order to quantify how device performance is affected when relaxation occurs we have therefore been investigating the electrical properties of dislocations at the p-n junction in Si/GeSi diodes.

In situ TEM Studies of agglomeration of sub-nanometer Ru layers in Ru/C multilayers

1992 ◽  
Vol 50 (1) ◽  
pp. 256-257
Author(s):  
Tai D. Nguyen ◽  
Ronald Gronsky ◽  
Jeffrey B. Kortright
Keyword(s):  
Layered Structure ◽  
Driving Force ◽  
High Energy ◽  
Superior Performance ◽  
In Situ Tem ◽  
Rayleigh Instability ◽  
Practical Applications ◽  
Transmission Electron ◽  
Diffraction Patterns

Nanometer period Ru/C multilayers are one of the prime candidates for normal incident reflecting mirrors at wavelengths < 10 nm. Superior performance, which requires uniform layers and smooth interfaces, and high stability of the layered structure under thermal loadings are some of the demands in practical applications. Previous studies however show that the Ru layers in the 2 nm period Ru/C multilayer agglomerate upon moderate annealing, and the layered structure is no longer retained. This agglomeration and crystallization of the Ru layers upon annealing to form almost spherical crystallites is a result of the reduction of surface or interfacial energy from die amorphous high energy non-equilibrium state of the as-prepared sample dirough diffusive arrangements of the atoms. Proposed models for mechanism of thin film agglomeration include one analogous to Rayleigh instability, and grain boundary grooving in polycrystalline films. These models however are not necessarily appropriate to explain for the agglomeration in the sub-nanometer amorphous Ru layers in Ru/C multilayers. The Ru-C phase diagram shows a wide miscible gap, which indicates the preference of phase separation between these two materials and provides an additional driving force for agglomeration. In this paper, we study the evolution of the microstructures and layered structure via in-situ Transmission Electron Microscopy (TEM), and attempt to determine the order of occurence of agglomeration and crystallization in the Ru layers by observing the diffraction patterns.

In situ TEM observations of melting in nanosized eutectic Pb-Cd inclusions embedded in Al

1996 ◽  
Vol 54 ◽  
pp. 986-987
Author(s):  
S. Hagège ◽  
U. Dahmen ◽  
E. Johnson ◽  
A. Johansen ◽  
V.S. Tuboltsev
Keyword(s):  
Electron Microscope ◽  
Melt Spinning ◽  
Ternary Alloys ◽  
Solid Matrix ◽  
Eutectic System ◽  
In Situ Tem ◽  
In Situ Observation ◽  
Orientation Relationships ◽  
Transmission Electron

Small particles of a low-melting phase embedded in a solid matrix with a higher melting point offer the possibility of studying the mechanisms of melting and solidification directly by in-situ observation in a transmission electron microscope. Previous studies of Pb, Cd and other low-melting inclusions embedded in an Al matrix have shown well-defined orientation relationships, strongly faceted shapes, and an unusual size-dependent superheating before melting.[e.g. 1,2].In the present study we have examined the shapes and thermal behavior of eutectic Pb-Cd inclusions in Al. Pb and Cd form a simple eutectic system with each other, but both elements are insoluble in solid Al. Ternary alloys of Al (Pb,Cd) were prepared from high purity elements by melt spinning or by sequential ion implantation of the two alloying additions to achieve a total alloying addition of up to lat%. TEM observations were made using a heating stage in a 200kV electron microscope equipped with a video system for recording dynamic behavior.

Postmortem and in situ TEM methods to study the mechanism of failure in controlled-morphology high-impact polystrene resin

1996 ◽  
Vol 54 ◽  
pp. 178-179
Author(s):  
R. C. Cieslinski ◽  
M. T. Dineen ◽  
J. L. Hahnfeld
Keyword(s):  
Poisson Ratio ◽  
Acrylonitrile Butadiene Styrene ◽  
High Impact ◽  
In Situ Tem ◽  
Styrene Copolymers ◽  
Controlled Morphology ◽  
Point Bend ◽  
Mechanism Of Failure ◽  
Impact Energies

Advanced Styrenic resins are being developed throughout the industry to bridge the properties gap between traditional HIPS (High Impact Polystyrene) and ABS (Acrylonitrile-Butadiene-Styrene copolymers) resins. These new resins have an unprecedented balance of high gloss and high impact energies. Dow Chemical's contribution to this area is based on a unique combination of rubber morphologies including labyrinth, onion skin, and core-shell rubber particles. This new resin, referred as a controlled morphology resin (CMR), was investigated to determine the toughening mechanism of this unique rubber morphology. This poster will summarize the initial studies of these resins using the double-notch four-point bend test of Su and Yee, tensile stage electron microscopy, and Poisson Ratio analysis of the fracture mechanism.

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