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.

Atom Clusters In A 2/1 Cubic Approximant Phase For Understanding The Structures Of Icosahedral Phases

1998 ◽  
Vol 553 ◽  
Author(s):  
K. HIRAGA
Keyword(s):  
Icosahedral Phase ◽  
The Body ◽  
Cubic Phase ◽  
Icosahedral Quasicrystal ◽  
Icosahedral Symmetry ◽  
Atom Cluster ◽  
Atom Clusters ◽  
Simple Cubic ◽  
Icosahedral Phases ◽  
Rotational Direction

AbstractTwo types of atom clusters found in the β-(A1PdMnSi) cubic phase, referred to as a 2/1 crystalline approximant, with a composition of approximately Al70Pd23Mn6Si1 which is near to the composition Al72Pd20Mn8 of the icosahedral phase, are discussed in detail for understanding the structure of the Al-Pd-Mn icosahedral phase. A large dodecahedral atom cluster located at the body-centered position can be divided into 19 atom shells with approximately icosahedral symmetry, and a dodecahedron of the 12th shell internally touches the surface of the cubic unit cell with a lattice constant of 2.0211 nm. At each vertex of the dodecahedron, a small icosahedral atom cluster consisting of 12 Al atoms surrounding a central Pd atom is located. The dodecahedron is connected to each other by edge-sharing, namely by sharing two small icosahedral atom clusters, along the twofold rotational direction, and forms a simple-cubic packing of the atom cluster in the β-(AlPdMnSi) cubic phase. Another atom cluster located at the origin fills up gaps of the simple-cubic packing of the large dodecahedral atom cluster. By using the dodecahedral and bridging atom clusters, the structure of the Al-Pd-Mn icosahedral quasicrystal is discussed.

Symmetry Changes At The Surface Of Al70Pd20Mn10

1998 ◽  
Vol 553 ◽  
Author(s):  
B. Bolliger ◽  
M. Erbudak ◽  
A. Hensch ◽  
A.R. Kortan ◽  
D.D. Vvedensky
Keyword(s):  
Room Temperature ◽  
Elevated Temperatures ◽  
Surface Composition ◽  
Structural Phase ◽  
Bulk Composition ◽  
Icosahedral Quasicrystal ◽  
Icosahedral Symmetry ◽  
Structural Phase Transitions ◽  
Structure Changes ◽  
Different Temperatures

AbstractSputtering with Ar+ ions induces structural phase transitions at the pentagonal surface of the icosahedral quasicrystal Al70Pd20Mn10. Sputtering at different temperatures changes the surface composition, thereby stabilizing different structures. At room temperature, the structure changes to body-centered cubic but, at elevated temperatures, it displays decagonal symmetry. In both cases, annealing the sample restores both the bulk composition and the icosahedral symmetry of the original surface.

On the Glass Formation in Systems Forming Icosahedral Quasicrystals

1986 ◽  
Vol 80 ◽  
Author(s):  
Leonid A. Bendersky ◽  
Stephen D. Ridder
Keyword(s):  
Glass Formation ◽  
Homogeneous Nucleation ◽  
Icosahedral Phase ◽  
Icosahedral Quasicrystal ◽  
Nucleation Behavior ◽  
Submicron Size ◽  
Icosahedral Quasicrystals ◽  
Rapidly Solidified ◽  
Alloy Systems

AbstractRapidly solidified micron and submicron size droplets of Al-14 a/o Mn have been used to study the possibility of glass formation and nucleation behavior of icosahedral phase. Homogeneous nucleation of icosahedral phase is assumed, based on the high grain density (>1015 mm−3). Extremely low nucleation resistance of icosahedral phase can be understood when possible topological similarities between liquid and icosahedral quasicrystal structures are considered. Configurationally frozen liquid in Al-Mn and similar alloy systems is questionable, implying that Al-Mn “glass” probably has a microquasicrystalline structure.

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.

Electron microscopy of crystalline structure in thermotropic random copolymers

1991 ◽  
Vol 49 ◽  
pp. 1054-1055
Author(s):  
Afzana Anwer ◽  
S. Eilidh Bedford ◽  
Richard J. Spontak ◽  
Alan H. Windle
Keyword(s):  
Electron Microscopy ◽  
Crystalline Structure ◽  
Liquid Crystalline ◽  
Elevated Temperatures ◽  
Random Copolymers ◽  
Molecular Characteristics ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Identical Monomer ◽  
Periodic Layer

Random copolyesters composed of wholly aromatic monomers such as p-oxybenzoate (B) and 2,6-oxynaphthoate (N) are known to exhibit liquid crystalline characteristics at elevated temperatures and over a broad composition range. Previous studies employing techniques such as X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) have conclusively proven that these thermotropic copolymers can possess a significant crystalline fraction, depending on molecular characteristics and processing history, despite the fact that the copolymer chains possess random intramolecular sequencing. Consequently, the nature of the crystalline structure that develops when these materials are processed in their mesophases and subsequently annealed has recently received considerable attention. A model that has been consistent with all experimental observations involves the Non-Periodic Layer (NPL) crystallite, which occurs when identical monomer sequences enter into register between adjacent chains. The objective of this work is to employ electron microscopy to identify and characterize these crystallites.

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.

A Metastable Crystalline Phase Coexisted with the Decagonal Quasicrystals in Rapidly Solidified Al-Ir Al-Pd and Al-Pt Alloys

1990 ◽  
Vol 48 (1) ◽  
pp. 572-573
Author(s):  
Wang Rong ◽  
Ma Lina ◽  
K.H. Kuo
Keyword(s):  
Metastable Phase ◽  
Hexagonal Phase ◽  
Icosahedral Quasicrystal ◽  
Decagonal Quasicrystal ◽  
Decagonal Phase ◽  
Decagonal Quasicrystals ◽  
Pt Alloy ◽  
Pt Alloys ◽  
Diffraction Patterns ◽  
Rapidly Solidified

Up to now, decagonal quasicrystals have been found in the alloys of whole Al-Pt group metals [1,2]. The present paper is concerned with the TEM study of a hitherto unreported hexagonal phase in rapidly solidified Al-Ir, Al-Pd and Al-Pt alloys.The ribbons of Al5Ir, Al5Pd and Al5Pt were obtained by spun-quenching. Specimens cut from the ribbons were ion thinned and examined in a JEM 100CX electron microscope. In both rapidly solidified Al5Ir and Al5Pd alloys, the decagonal quasicrystal, with rosette or dendritic morphologies can be easily identified by its electron diffraction patterns(EDPs). The EDPs of the decagonal phase for the two alloys are quite similar. However, the existance of decagonal quasicrystal in the Al-Pt alloy has not been verified by our TEM study. It is probably for the reason that the cooling rate is not great enough for the Al5Pt alloy to form the decagonal phase. During the TEM study, a metastable hexagonal phase has been observed in the Al5Ir, Al5Pd and Al5Pt alloys. The lattic parameters calculated from the X-ray powder data of this phase are a=1.229 and c=2.647nm(Al-Pd) and a=1.231 and c=2.623nm(Al-Ir). The composition of this phase was determined by EDS analysis as Al4(Ir, Pd or Pt). It coexists with the decagonal phase in the alloys and transformed to other stable crystalline phases on heating to high temperature. A comparison between the EDPs of the hexagonal and the decagonal phase are shown in Fig.l. Fig. 1(a) is the EDPs of the decagonal phase in various orientions and the EDPs of the hexagonal phase are shown in Fig.1(b), in a similar arrangement as Fig.1(a). It can be clearly seen that the EDPs of the hexagonal phase, especially the distribution of strong spots, are quite similar to their partners of the decagonal quasicrystal in Fig.1(a). All the angles, shown in Fig.l, between two corresponding EDPs are very close to each other. All of these seem strongly to point out that a close structural relationshipexists between these two phases:[110]//d10 [001]//d2(D) //d2 (P)The structure of α-AlFeSi is well known [3] and the 54-atom Mackay icosahedron with double icosahedral shells in the α-AlFeSi structure [4] have been used to model the icosahedral quasicrystal structure. Fig.2(a) and (b) show, respectively, the [110] and [001] projections of the crystal structure of α- AlFeSi, and decagon-pentagons can easily be identified in the former and hexagons in the latter. In addition, the optical transforms of these projections show clearly decagons and hexagons of strong spots, quite similar to those in [110] and [001] EDPs in Fig.1(b). This not only proves the Al(Ir, Pt, Pd) metastable phase being icostructural with the α-AlFeSi phase but also explains the orientation relationship mentioned above.

Probing the Small-Scale Plasticity of an Icosahedral Quasicrystal I-Al-Pd-Mn at Elevated Temperatures

2020 ◽  
Author(s):  
Changjun Cheng ◽  
Yuan Xiao ◽  
Michel J.R. Haché ◽  
Zhiying Liu ◽  
Alla S. Sologubenko ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Small Scale ◽  
Icosahedral Quasicrystal

Electric-Field Effects on Reactions Between Oxides

1997 ◽  
Vol 481 ◽  
Author(s):  
Matthew T. Johnson ◽  
Shelley R. Gilliss ◽  
C. Barry Carter
Keyword(s):  
Solid State ◽  
Electric Field ◽  
Elevated Temperatures ◽  
Ionic Current ◽  
Reaction Rates ◽  
Solid State Reactions ◽  
Interfacial Stability ◽  
Electric Field Effects ◽  
Thin Film Diffusion ◽  
Microscopy Techniques

ABSTRACTThin films of In2O3 and Fe2O3 have been deposited on (001) MgO using pulsed-laser deposition (PLD). These thin-film diffusion couples were then reacted in an applied electric field at elevated temperatures. In this type of solid-state reaction, both the reaction rate and the interfacial stability are affected by the transport properties of the reacting ions. The electric field provides a very large external driving force that influences the diffusion of the cations in the constitutive layers. This induced ionic current causes changes in the reaction rates, interfacial stability and distribution of the phases. Through the use of electron microscopy techniques the reaction kinetics and interface morphology have been investigated in these spinel-forming systems, to gain a better understanding of the influence of an electric field on solid-state reactions.

scholarly journals Microstructural Characterization and Mechanical Property of Al-Li Plate Produced by Centrifugal Casting Method

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 966
Author(s):  
Qingle Tian ◽  
Kai Deng ◽  
Zhishuai Xu ◽  
Ke Han ◽  
Hongxing Zheng
Keyword(s):  
Centrifugal Casting ◽  
High Strength ◽  
Microstructural Characterization ◽  
Fracture Morphology ◽  
Total Elongation ◽  
Mechanical Anisotropy ◽  
Tensile Fracture ◽  
Casting Method ◽  
Scanning Calorimetry ◽  
Strengthening Phases

Using a centrifugal casting method, along with deformation and aging, we produced a high-strength, low-anisotropy Al-Li plate. The electron probe microanalysis, transmission electron microscope, differential scanning calorimetry, and X-ray diffraction were used to clarify the evolution of strengthening phases. Experimental results showed that centrifugal-cast Al-Li plate consisted of intragrain δ′—(Al,Cu)3Li precipitate and interdendritic θ′—Al2Cu particles. After cold-rolling to a reduction ratio of 60% and annealing at 800 K for 90 min, both primary θ′ and δ′ were dissolved in solid solution. Aging at 438 K for 60 h led to the formation of two kinds of precipitates (needle-like T1—Al2CuLi and spherical δ′ in two sizes), which acted as the main strengthening phases. The average values of ultimate tensile strength and yield strength for the anneal-aged plate reached 496 MPa and 408 MPa, with a total elongation of 3.9%. The anneal-aged plate showed mechanical anisotropy of less than 5%. The tensile fracture morphology indicated a typical intergranular fracture mode.

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