Orientation-dependent equilibrium film thickness at interphase boundaries in ceramic-ceramic composites

Samples of low-nickel Zircaloy-2 (material MLI-788-see(1)), when anodically polarized in neutral 5 wt% NaCl solutions, were found to be susceptible to pitting and stress corrosion cracking. The SEM revealed that pitting of stressed samples was occurring below a 2000Å thick surface film which behaved differently from normal zirconium dioxide in that it did not display interference colours. Since the initial film thickness was approximately 65Å, attempts were made to examine the product film by transmission electron microscopy to deduce composition and how the corrosion environment could penetrate the continuous layer.

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Microstructural Evaluation of Silicon Carbide Whisker Reinforced Alumina Fabricated with Carbon-Coated Whiskers

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100088919 ◽

1991 ◽

Vol 49 ◽

pp. 920-921

Author(s):

K. B. Alexander ◽

P. F. Becher

Keyword(s):

Silicon Carbide ◽

High Resolution Electron Microscopy ◽

Ceramic Composites ◽

Interface Debonding ◽

Resolution Electron ◽

Microstructural Evaluation ◽

Carbon Coated ◽

Electron Energy Loss ◽

Interfacial Films ◽

Debonding Process

The presence of interfacial films at the whisker-matrix interface can significantly influence the fracture toughness of ceramic composites. The film may alter the interface debonding process though changes in either the interfacial fracture energy or the residual stress at the interface. In addition, the films may affect the whisker pullout process through the frictional sliding coefficients or the extent of mechanical interlocking of the interface due to the whisker surface topography.Composites containing ACMC silicon carbide whiskers (SiCw) which had been coated with 5-10 nm of carbon and Tokai whiskers coated with 2 nm of carbon have been examined. High resolution electron microscopy (HREM) images of the interface were obtained with a JEOL 4000EX electron microscope. The whisker geometry used for HREM imaging is described in Reference 2. High spatial resolution (< 2-nm-diameter probe) parallel-collection electron energy loss spectroscopy (PEELS) measurements were obtained with a Philips EM400T/FEG microscope equipped with a Gatan Model 666 spectrometer.

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HREM interface studies in SiC-whisker-reinforced Al2O3 and Si3N4 ceramics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100105734 ◽

1988 ◽

Vol 46 ◽

pp. 734-735

Author(s):

W. Braue ◽

R.W. Carpenter ◽

D.J. Smith

Keyword(s):

Analytical Data ◽

Base Material ◽

High Strength ◽

Ceramic Composites ◽

Good Thermal Stability ◽

All Ceramic ◽

Sic Whiskers ◽

Base Composite ◽

C 30 ◽

Si3n4 Ceramics

Whisker and fiber reinforcement has been established as an effective toughening concept for monolithic structural ceramics to overcome limited fracture toughness and brittleness. SiC whiskers in particular combine both high strength and elastic moduli with good thermal stability and are compatible with most oxide and nonoxide matrices. As the major toughening mechanisms - crack branching, deflection and bridging - in SiC whiskenreinforced Al2O3 and Si3N41 are critically dependent on interface properties, a detailed TEM investigation was conducted on whisker/matrix interfaces in these all-ceramic- composites.In this study we present HREM images obtained at 400 kV from β-SiC/α-Al2O3 and β-SiC/β-Si3N4 interfaces, as well as preliminary analytical data. The Al2O3- base composite was hotpressed at 1830 °C/60 MPa in vacuum and the Si3N4-base material at 1725 °C/30 MPa in argon atmosphere, respectively, adding a total of 6 vt.% (Y2O3 + Al2O3) to the latter to promote densification.

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(111) Monocrystalline Nickel Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095819 ◽

1972 ◽

Vol 30 ◽

pp. 512-513

Author(s):

T.E. Pratt ◽

R.W. Vook

Keyword(s):

Film Thickness ◽

Deposition Rate ◽

Room Temperature ◽

Narrow Range ◽

High Vacuum ◽

Residual Pressure ◽

Temperature Dependent ◽

Deposition Parameters ◽

Transmission Electron ◽

Substrate Temperatures

(111) oriented thin monocrystalline Ni films have been prepared by vacuum evaporation and examined by transmission electron microscopy and electron diffraction. In high vacuum, at room temperature, a layer of NaCl was first evaporated onto a freshly air-cleaved muscovite substrate clamped to a copper block with attached heater and thermocouple. Then, at various substrate temperatures, with other parameters held within a narrow range, Ni was evaporated from a tungsten filament. It had been shown previously that similar procedures would yield monocrystalline films of CU, Ag, and Au.For the films examined with respect to temperature dependent effects, typical deposition parameters were: Ni film thickness, 500-800 A; Ni deposition rate, 10 A/sec.; residual pressure, 10-6 torr; NaCl film thickness, 250 A; and NaCl deposition rate, 10 A/sec. Some additional evaporations involved higher deposition rates and lower film thicknesses.Monocrystalline films were obtained with substrate temperatures above 500° C. Below 450° C, the films were polycrystalline with a strong (111) preferred orientation.

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Biomimetic materials: An introduction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100129735 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1020-1021 ◽

Cited By ~ 1

Author(s):

M. Sarikaya ◽

J. T. Staley ◽

I. A. Aksay

Keyword(s):

Self Assembly ◽

Structural Control ◽

Hierarchical Structures ◽

Ceramic Composites ◽

Advanced Materials ◽

Length Scale ◽

Spider Webs ◽

Biomimetic Materials ◽

Synthetic Materials ◽

All Ceramic

Biomimetics is an area of research in which the analysis of structures and functions of natural materials provide a source of inspiration for design and processing concepts for novel synthetic materials. Through biomimetics, it may be possible to establish structural control on a continuous length scale, resulting in superior structures able to withstand the requirements placed upon advanced materials. It is well recognized that biological systems efficiently produce complex and hierarchical structures on the molecular, micrometer, and macro scales with unique properties, and with greater structural control than is possible with synthetic materials. The dynamism of these systems allows the collection and transport of constituents; the nucleation, configuration, and growth of new structures by self-assembly; and the repair and replacement of old and damaged components. These materials include all-organic components such as spider webs and insect cuticles (Fig. 1); inorganic-organic composites, such as seashells (Fig. 2) and bones; all-ceramic composites, such as sea urchin teeth, spines, and other skeletal units (Fig. 3); and inorganic ultrafine magnetic and semiconducting particles produced by bacteria and algae, respectively (Fig. 4).

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The method of replication affects metal film granularity and resolution

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100155517 ◽

1989 ◽

Vol 47 ◽

pp. 708-709

Author(s):

George C. Ruben

Keyword(s):

Electron Beam ◽

High Resolution ◽

Film Thickness ◽

Single Molecule ◽

Metal Film ◽

Vertical Surface ◽

High Resolution Imaging ◽

Controllable Factors ◽

Resolution Imaging

Single molecule resolution in electron beam sensitive, uncoated, noncrystalline materials has been impossible except in thin Pt-C replicas ≤ 150Å) which are resistant to the electron beam destruction. Previously the granularity of metal film replicas limited their resolution to ≥ 20Å. This paper demonstrates that Pt-C film granularity and resolution are a function of the method of replication and other controllable factors. Low angle 20° rotary , 45° unidirectional and vertical 9.7±1 Å Pt-C films deposited on mica under the same conditions were compared in Fig. 1. Vertical replication had a 5A granularity (Fig. 1c), the highest resolution (table), and coated the whole surface. 45° replication had a 9Å granulartiy (Fig. 1b), a slightly poorer resolution (table) and did not coat the whole surface. 20° rotary replication was unsuitable for high resolution imaging with 20-25Å granularity (Fig. 1a) and resolution 2-3 times poorer (table). Resolution is defined here as the greatest distance for which the metal coat on two opposing faces just grow together, that is, two times the apparent film thickness on a single vertical surface.

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Observation of solid-state reaction between a thin yttria film and a (0001) α-alumina substrate

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100170955 ◽

1994 ◽

Vol 52 ◽

pp. 644-645

Author(s):

J. R. Heffelfinger ◽

C. B. Carter

Keyword(s):

Electron Microscopy ◽

Solid State ◽

Solid State Reaction ◽

Yttrium Aluminum Garnet ◽

Secondary Phase ◽

Ceramic Composites ◽

Alumina Substrate ◽

Transmission Electron ◽

Alumina Fibers ◽

Optical Applications

Transmission-electron microscopy (TEM), scanning-electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) were used to investigate the solid-state reaction between a thin yttria film and a (0001) α-alumina substrate. Systems containing Y2O3 (yttria) and Al2O3 (alumina) are seen in many technologically relevant applications. For example, yttria is being explored as a coating material for alumina fibers for metal-ceramic composites. The coating serves as a diffusion barrier and protects the alumina fiber from reacting with the metal matrix. With sufficient time and temperature, yttria in contact with alumina will react to form one or a combination of phases shown by the phase diagram in Figure l. Of the reaction phases, yttrium aluminum garnet (YAG) is used as a material for lasers and other optical applications. In a different application, YAG is formed as a secondary phase in the sintering of AIN. Yttria is added to AIN as a sintering aid and acts as an oxygen getter by reacting with the alumina in AIN to form YAG.

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