Microstructural Variations in Melt-Spun Rapidly Solidified Ribbons

Author(s):  
L. A. Bendersky ◽  
W. J. Boettinger

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.

1990 ◽  
Vol 186 ◽  
Author(s):  
W. J. Park ◽  
S. Ahn ◽  
N.J. Kim

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.


Author(s):  
G. M. Michal ◽  
T. K. Glasgow ◽  
T. J. Moore

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.


Author(s):  
S.R. Summerfelt ◽  
C.B. Carter

The wustite-spinel interface can be viewed as a model interface because the wustite and spinel can share a common f.c.c. oxygen sublattice such that only the cations distribution changes on crossing the interface. In this study, the interface has been formed by a solid state reaction involving either external or internal oxidation. In systems with very small lattice misfit, very large particles (>lμm) with coherent interfaces have been observed. Previously, the wustite-spinel interface had been observed to facet on {111} planes for MgFe2C4 and along {100} planes for MgAl2C4 and MgCr2O4, the spinel then grows preferentially in the <001> direction. Reasons for these experimental observations have been discussed by Henriksen and Kingery by considering the strain energy. The point-defect chemistry of such solid state reactions has been examined by Schmalzried. Although MgO has been the principal matrix material examined, others such as NiO have also been studied.


Author(s):  
W. A. Chiou ◽  
N. L. Jeon ◽  
Genbao Xu ◽  
M. Meshii

For many years amorphous metallic alloys have been prepared by rapid quenching techniques such as vapor condensation or melt quenching. Recently, solid-state reactions have shown to be an alternative for synthesizing amorphous metallic alloys. While solid-state amorphization by ball milling and high energy particle irradiation have been investigated extensively, the growth of amorphous phase by cold-rolling has been limited. This paper presents a morphological and structural study of amorphization of Cu and Ti foils by rolling.Samples of high purity Cu (99.999%) and Ti (99.99%) foils with a thickness of 0.025 mm were used as starting materials. These thin foils were cut to 5 cm (w) × 10 cm (1), and the surface was cleaned with acetone. A total of twenty alternatively stacked Cu and Ti foils were then rolled. Composite layers following each rolling pass were cleaned with acetone, cut into half and stacked together, and then rolled again.


Author(s):  
P. G. Kotula ◽  
D. D. Erickson ◽  
C. B. Carter

High-resolution field-emission-gun scanning electron microscopy (FESEM) has recently emerged as an extremely powerful method for characterizing the micro- or nanostructure of materials. The development of high efficiency backscattered-electron detectors has increased the resolution attainable with backscattered-electrons to almost that attainable with secondary-electrons. This increased resolution allows backscattered-electron imaging to be utilized to study materials once possible only by TEM. In addition to providing quantitative information, such as critical dimensions, SEM is more statistically representative. That is, the amount of material that can be sampled with SEM for a given measurement is many orders of magnitude greater than that with TEM.In the present work, a Hitachi S-900 FESEM (operating at 5kV) equipped with a high-resolution backscattered electron detector, has been used to study the α-Fe2O3 enhanced or seeded solid-state phase transformations of sol-gel alumina and solid-state reactions in the NiO/α-Al2O3 system. In both cases, a thin-film cross-section approach has been developed to facilitate the investigation. Specifically, the FESEM allows transformed- or reaction-layer thicknesses along interfaces that are millimeters in length to be measured with a resolution of better than 10nm.


Author(s):  
F. Ma ◽  
S. Vivekanand ◽  
K. Barmak ◽  
C. Michaelsen

Solid state reactions in sputter-deposited Nb/Al multilayer thin films have been studied by transmission and analytical electron microscopy (TEM/AEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The Nb/Al multilayer thin films for TEM studies were sputter-deposited on (1102)sapphire substrates. The periodicity of the films is in the range 10-500 nm. The overall composition of the films are 1/3, 2/1, and 3/1 Nb/Al, corresponding to the stoichiometric composition of the three intermetallic phases in this system.Figure 1 is a TEM micrograph of an as-deposited film with periodicity A = dA1 + dNb = 72 nm, where d's are layer thicknesses. The polycrystalline nature of the Al and Nb layers with their columnar grain structure is evident in the figure. Both Nb and Al layers exhibit crystallographic texture, with the electron diffraction pattern for this film showing stronger diffraction spots in the direction normal to the multilayer. The X-ray diffraction patterns of all films are dominated by the Al(l 11) and Nb(l 10) peaks and show a merging of these two peaks with decreasing periodicity.


1990 ◽  
Vol 51 (C4) ◽  
pp. C4-121-C4-130
Author(s):  
U. KÖSTER ◽  
R. PRIES ◽  
G. BEWERNICK ◽  
B. SCHUHMACHER ◽  
M. BLANK-BEWERSDORFF

2016 ◽  
pp. 3287-3297
Author(s):  
Tarek El Ashram ◽  
Ana P. Carapeto ◽  
Ana M. Botelho do Rego

Tin-bismuth alloy ribbons were produced using melt-spinning technique. The two main surfaces (in contact with the rotating wheel and exposed to the air) were characterized with Optical Microscopy and AFM, revealing that the surface exposed to the air is duller (due to a long-range heterogeneity) than the opposite surface. Also the XPS chemical composition revealed many differences between them both on the corrosion extension and on the total relative amounts of tin and bismuth. For instance, for the specific case of an alloy with a composition Bi-4 wt % Sn, the XPS atomic ratios Sn/Bi are 1.1 and 3.7 for the surface in contact with the rotating wheel and for the one exposed to air, respectively, showing, additionally, that a large segregation of tin at the surface exists (nominal ratio should be 0.073). This segregation was interpreted as the result of the electrochemical process yielding the corrosion products.


1997 ◽  
Vol 481 ◽  
Author(s):  
Matthew T. Johnson ◽  
Shelley R. Gilliss ◽  
C. Barry Carter

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.


1997 ◽  
Vol 52 (5) ◽  
pp. 663-668 ◽  
Author(s):  
B. Mertens ◽  
Hk. Müller-Buschbaum

Abstract Single crystals of I RbCd4V3O12 and TlCd4V3O12 II have been prepared by solid state reactions in closed iron tubes. The compounds crystallize closely related to the Johillerite structure in the space group C62h- C2/c with I: a = 13.058(3); b - 13.528(3), c = 7 .0 6 0 (2 )Å , β = 114.88(2)°; II: a = 12.999(6), b = 13.527(7), c = 7.055(3) Å , β = 114.88(4)°, Z = 4. Special features are the loss of Cu2+ in order to gain an additional Cd2+ position. The crystal structure is discussed with respect to related compounds of the Johillerite type.


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