Microstructure of Ceramics

7 Key excerpts on "Microstructure of Ceramics"

• 

  eBook - ePub

  Ceramics Science and Technology, Volume 1

  Structures

  • Ralf Riedel, I-Wei Chen, Ralf Riedel, I-Wei Chen(Authors)
  • 2015(Publication Date)
  • Wiley-VCH

    (Publisher)

  6 Microstructural Design of Ceramics: Theory and Experiment

  Gayle S. Painter and Paul F. Becher

  6.1 Overview

  The chemical bonding and electronic structure of condensed matter form the fundamental basis for an understanding of the diverse properties of materials. An even greater spectrum of properties, phenomena and behavior comes from the coupling of these properties over various length scales, giving rise to the materials’ microstructure. Ceramic materials possess compositional complexity, and also display a rich diversity of properties and behavior as a consequence of the resulting variable microstructure. Much is to be learned by understanding how variations in the properties of materials are associated with the underlying microstructure. In this chapter, the current state of understanding of: (i) what determines microstructure in ceramics; and (ii) how microstructure affects observed properties and behavior, is examined. Clearly, although microstructural effects on the electronic properties of ceramics may be important, in this chapter the discussion is limited to structural ceramics and mechanical behavior. The aim of this chapter is to describe how microstructure is determined by fundamental materials characteristics, and how an understanding of microstructure is enhanced through theory and modeling.

  The first question, therefore, is what is meant by the term microstructure? Microstructure can imply several things because: (i) micro is frequently used in a dimensional sense (smallness) that is more general than the micron scale; and (ii) structure indicates spatial (or temporal) inhomogeneity. In this chapter, the term microstructure is used in this general sense: a material property inhomogeneity over length scales extending from sub-nanometer to millimeter. Over the past decade or two, the term nanostructure has become pervasive, although here the dimensional aspect is usually implied. For length

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  eBook - PDF

  An Introduction to Ceramic Science

  The Commonwealth and International Library: Materials Science and Technology (Ceramics Division)

  • D. W. Budworth, G. Arthur(Authors)
  • 2016(Publication Date)
  • Pergamon

    (Publisher)

  Microstructural studies would be required to decide which of the two descriptions applied to any particular case. Although the discussion here has been carried out in terms of electrical conductivity, the same three models are used for mechanical properties, thermal conductivity, and other physical properties. References for Further Reading BUDWORTH, D. W., Principles of ceramic density measurement, /. Brit. Ceram. Soc, 1,448-461,1964. 164 An Introduction to Ceramic Science SMITH, C. S., Some elementary principles of polycrystalline microstructure, Metallurgical Reviews, 9,1-48, 1964. Microstructure of Ceramic Materials, U.S. National Bureau of Standards Miscellaneous Publication 257, 1964. Stereology (Proceedings of the Second International Congress for Stereology), ed. H. Elias, New York: Springer Verlag, 1967.

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  eBook - ePub

  Encyclopedia of Glass Science, Technology, History, and Culture

  • Pascal Richet(Author)
  • 2021(Publication Date)
  • Wiley-American Ceramic Society

    (Publisher)

  2.3 Microstructure Analysis of Glasses and Glass Ceramics Christian Patzig and Thomas Höche Fraunhofer Institute for Microstructure of Materials and Systems IMWS, Halle (Saale), Germany 1 Introduction A homogeneous glass by definition lacks a microstructure at a scale larger than a few nanometers. As soon as actual inhomogeneities occur, in contrast, a detailed picture of their size, distribution, composition, and spatial arrangement becomes important to understand the properties of the material. In turn, the improved capabilities of microstructural studies in terms of spatial and elemental resolution are becoming increasingly important to optimize crystallization or phase separation and to achieve the desired microstructure and associated properties (Chapter 7.11). As a matter of fact, the beauty and challenge of glasses and glass ceramics is their diversity and complexity. The purpose of this chapter thus is to review the main microstructural methods commonly used to study inhomogeneous glass‐based materials. In preamble, however, it is important to note that studying extremely small volumes in great detail can result in “knowing everything about nothing.” In other words, it is critically important to make sure that the information gathered locally is actually representative for larger volumes. To achieve this goal, highly resolved information must be combined with additional integral measurements to get a broad picture. In addition, artifacts introduced upon either preparation or investigation of the sample must be avoided. And one should also be extremely careful with in situ microstructural experiments where, because of dramatic differences in the surface‐to‐volume ratio, annealing can easily lead to results not observed in the bulk

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  eBook - ePub

  Bioceramics: For Materials Science and Engineering

  • Saad B. H. Farid(Author)
  • 2018(Publication Date)
  • Woodhead Publishing

    (Publisher)

  2

  Structure, microstructure, and properties of bioceramics

  Abstract

  This chapter explains the source of the properties of ceramic, glass, cement, and composite materials, and elucidates the reasons behind the choice of certain materials as bioceramics. Thus the material characteristics, chemistry, crystal structure, and microstructure of familiar bioceramics are introduced. Comprehension of these characteristics helps in recognizing the origin of the materials' properties, such as bioactivity, degradation, and mechanical properties. In addition, such a background aids in designing new materials and microstructures that better fit the target applications of bioceramics. Illustrative definitions, figures, and tables, which are found in sound literature, are included in the chapter and can be used as an easy and fast access to reference data.

  Keywords

  Bioceramics; Bone cements; Bone substitutes; In vitro test; Microstructure; Properties; Structure

  2.1. Oxide ceramics

  2.1.1. Alumina

  Alumina (Al2 O3 ) may be found in many metastable phases (γ, η, θ, ρ, and χ) other than the thermodynamically stable phase α-alumina. The metastable phases transform into the α-phase upon heat treatment above 1200°C. The oxygen atoms of α-alumina are arranged in hexagonal close-packed planes, which are intercalated with aluminum planes. The crystal structure of α-alumina is hexagonal and can also be expressed as rhombohedral with a space group of R3c. Fig. 2.1 shows the hexagonal close-packed structure of oxygen (O− ) ions. Aluminum (Al+

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  eBook - ePub

  Porosity of Ceramics

  Properties and Applications

  • Roy W. Rice(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Fig. 8.15 ). The very high b values are suggested to be due to interfacial pores between the fibers and the matrix generally being among the last to be eliminated and having by far the most effect on mechanical properties. On the other hand, much of the earlier porosity eliminated in processing is that in the matrix, which has less, often much less, effect on properties, hence lower, possibly much lower, b values. Within this bilinear trend, there is some indication of expected effects of pore character, i.e., lower b values in both branches for more spherical pores in the matrix. Progressively lower degrees of such interfacial pore effects in platelet, whisker, and particulate composites need to be considered, along with other microstructural factors such as the relative sizes and morphologies of the matrix and dispersed phases.

  Finally, microcracking occurs in many ceramic composite materials, e.g., in some porcelains and crystallized glasses, and particularly in many more modern composites, which are often selected to obtain some microcrack toughening. While composite microstructures can aid in defining the amount and character of microcracking, they also introduce complexities such as microcrack formation in single-phase areas of anisotropic grains as well as with abutting grains of different phases. Another complexity is the nature of the microcracks: while intergranular ones are often likely and almost universally assumed, they can often have considerable transgranular character. Models for elastic moduli, which are determined mainly by preexisting microcracks, show promise of aiding microcrack characterization along with giving guidance to the moduli as a function of composite composition. A further complexity is the extent to which microcracks are preexisting or form in association with propagation of a larger crack and the effects of crack size and extent of propagation. Comparison of fracture properties such as strength and fracture toughness with elastic moduli as a function of composition and microstructure and careful measurements of sample volume or thermal expansion as a function of stressing can be good indicators of stress-crack induced microcracking. Some comparison of preexisting versus crack propagation-induced microcracking has been made showing some similarities and some differences in toughness changes; however, the key issue of the effects of crack scale and character of propagation on fracture toughness versus strength has not been adequately addressed. The common assumption that strength behavior follows that of fracture toughness, which unfortunately has lead to a paucity of strength measurements, is seriously questioned. While more study is needed, strengths should be measured and their values or trends not assumed from toughness values. This is critical since some strength behavior has opposite microstructural trends from that of fracture toughness, i.e., that strength decreases as toughness increases. Furthermore, increased toughness may decrease, not increase, the Weibull modulus (m), and where m does increase in composites, it may arise from other sources than the increased toughness. The increased toughness in composites is of greater use in improving resistance to serious thermal shock damage, i.e., analogous to effects of porosity. Porosity and rnicrocrack effects can often be independent, as commonly assumed; however, there are clearly important cases where the two have had significant interactive effects (beneficial for thermal shock), so such interactions must be considered.

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  Laser Processing of Engineering Materials

  Principles, Procedure and Industrial Application

  • John Ion(Author)
  • 2005(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Atomic packing and bonding influences material properties, and electronic configurations play a central role in determining the interaction between the photons of the laser beam and the material. The microstructure, on the order of micrometres (10 − 6 m), is governed by arrangements of atoms and molecules in discrete phases. Microstructural changes are induced through the thermal cycles generated during laser processing, which can be illustrated using various phase transformation diagrams. The macrostructure, on the order of millimetres (10 − 3 m), is used as the basis for design calculations to determine engineering performance. Fundamental mechanical and thermal properties are influenced by structure on all three levels. The chapter also introduces the most common industrial materials. Their composition, structure and properties are described, to reveal the philosophy that underlies their design. Strengthening mechanisms, introduced by alloying or thermomechanical treatments, are described – these are affected by the thermal cycles induced during laser processing. These materials make regular appearances in the chapters that follow. Those properties that control the thermal response of materials are displayed on charts, which indicate behaviour during laser processing and play an important role in the selection of materials for laser processing. 140 Laser Processing of Engineering Materials Atomic Structure The atomic structure of engineering materials describes the bonding between atoms, the packing of the atoms, and the distribution of electrons. Metals and Alloys Bonding The atomic structure of metals and alloys is determined by the metallic bond. Electrons are freely shared by atomic nuclei (positive ions). On average, each nucleus is surrounded by sufficient electrons to maintain a full outer shell. Electrostatic attraction between the positive nuclei and the negative electron ‘cloud’ constitutes the metallic bond.

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  Metal and Ceramic Matrix Composites

  • Brian Cantor, Fionn .P.E Dunne, Ian C Stone, Brian Cantor, Fionn .P.E Dunne, Ian C Stone(Authors)
  • 2003(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 17 Microstructure and performance limits of ceramic matrix composites M H Lewis Introduction The disappointing degree of market penetration for monolithic engineering ceramics is due to a combination of economic factors and the reluctance to apply statistical failure criteria to critical components with fracture toughness values generally below 10 MPa m 1 = 2 . The concept of damage-tolerance using long fibres in ceramic matrix composites (CMCs) was demonstrated in the 1970s, following the evolution of high-strength carbon fibres. Further development of ceramic matrix composites was promoted by the availability of polymer-precursor fibres based on SiC (Nicalon and Tyranno) and the fortuitous in situ formation of carbon-rich debond interfaces within silicate matrices. This precipated the successful theoretical modelling of mechanical behaviour in parallel with experiments on SiC/silicate and chemical vapour infiltrated SiC/SiC systems. This chapter presents a brief survey of the key microstructural parameters required for ideal ceramic matrix composite per-formance and highlights some of the technical and microstructural problems which inhibit engineering application. Current potential for applications in industrial gas turbines is discussed in chapter 5. Microstructure, modelling and performance Stress–strain behaviour An example of a tensile stress–strain ' – curve at constant imposed strain rate _ for a real composite [1] may be used to demonstrate the relationship between macroscopic ceramic matrix composite properties and interfacial microscopic parameters and to introduce the terminology used in the literature. Figure 17.1 shows a stress–strain curve for a unidirectional (UD) SiC (Tyranno) 299 fibre architecture within an alumino-silicate glass–ceramic matrix (barium magnesium aluminium silicate).

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