This is a more comprehensive list of learning objectives than at the beginning of each chapter. List of classroom demonstrations and lab experiments. and experiments depict phenomena and/or illustrate principles covered in the book; references are also provided giving more detailed accounts of it.
HISTORICAL PERSPECTIVE
Name the four components that are involved in the design, manufacture and use of materials and briefly describe the interrelationships between these components. Cite three criteria that are important in the materials selection process. a) List the three main classifications of solid materials and then cite the distinguishing chemical feature of each.
MATERIALS SCIENCE AND ENGINEERING
This paradigm, formulated in the 1990s, is essentially the core of the discipline of materials science and engineering. The disk on the right is opaque - that is, no light passes through it.
WHY STUDY MATERIALS SCIENCE AND ENGINEERING?
The failure of a number of World War II Liberty ships4 is a well-known and dramatic example of the brittle failure of steel that was thought to be ductile.5 Some early ships experienced structural damage when cracks and hulls developed in their decks. 5 Ductile metals fail after relatively large rates of permanent deformation; however, fracture of brittle materials is accompanied by very little, if any, permanent deformation.
CLASSIFICATION OF MATERIALS
With regard to mechanical properties, these materials are relatively stiff (Figure 1.5) and strong (Figure 1.6), yet ductile (i.e. capable of large amounts of deformation without fracture) and resist fracture (Figure 1.7). for their widespread use in structural applications. For example, metals are extremely good conductors of electricity (Figure 1-8) and heat, and are not transparent to visible light; a polished metal surface has a shiny appearance.
With regard to optical characteristics, ceramics can be transparent, translucent or opaque (Figure 1.1), and some oxide ceramics (e.g. Fe3O4) show magnetic behavior. These materials are generally of low density (Figure 1.4), while their mechanical characteristics generally do not match those of the metals and ceramics - they are not as stiff or strong as these.
Glass is impermeable to the passage of carbon dioxide, is a relatively cheap material and can be recycled, but it cracks and breaks easily and glass bottles are relatively heavy. While plastic is relatively strong, can be made optically transparent, is cheap and light, and can be recycled, it is not as impervious to carbon dioxide as aluminum and glass.
These advanced materials are usually traditional materials whose properties have been improved, as well as newly developed, high-performance materials. The properties and applications of many of these advanced materials—for example, materials used in lasers, batteries, magnetic information storage, liquid crystal displays (LCDs), and optical fibers—are also discussed in subsequent chapters.
ADVANCED MATERIALS
Advanced materials include semiconductors, biomaterials and what we can call the materials of the future (i.e. smart materials and nanoengineered materials), which we discuss next. Furthermore, the electrical properties of these materials are extremely sensitive to the presence of small concentrations of impurity atoms, for which the concentrations can be controlled over very small spatial areas.
We call this the bottom-up approach and studying the properties of these materials is called nanotechnology.13. Because of these unique and unusual properties, nanomaterials are finding niches in electronic, biomedical, sports, energy production and other industrial applications.
MODERN MATERIALS’ NEEDS
Before the advent of nanomaterials, the general procedure scientists used to understand the chemistry and physics of materials was to start by studying large and complex structures and then investigate the fundamental building blocks of these smaller and simpler structures. Some of these effects are quantum mechanical in origin, while others are related to surface phenomena: the proportion of atoms on a particle's surface increases dramatically as its size decreases.
SUMMARY
Describe the important quantum-mechanical principle that relates to electron energies
- INTRODUCTION
- FUNDAMENTAL CONCEPTS
- ELECTRONS IN ATOMS
- Electrons in Atoms • 23
- Electrons in Atoms • 25
- Electrons in Atoms • 27
- THE PERIODIC TABLE
- The Periodic Table • 29
- BONDING FORCES AND ENERGIES
- PRIMARY INTERATOMIC BONDS
- Primary Interatomic Bonds • 33
- Primary Interatomic Bonds • 35
- Primary Interatomic Bonds • 37
- Secondary Bonding or van der Waals Bonding • 39
- SECONDARY BONDING OR VAN DER WAALS BONDING
- Secondary Bonding or van der Waals Bonding • 41
- Mixed Bonding • 43
- MIXED BONDING
- MOLECULES
- BONDING TYPE-MATERIAL CLASSIFICATION CORRELATIONS
The centers of the two atoms remain separated by the equilibrium distance r0, as shown in Figure 2.10a. To achieve this configuration, one 2s orbital is mixed with two of the three 2p orbitals - the third p orbital remains unhybridized; this is shown in Figure 2.16.
Equation Summary
List of Symbols
Important Terms and Concepts
It should be noted that the hexagonal symmetry of magnesium's hexagonal close-packed crystal structure [shown in (c)] is indicated by the diffraction spot pattern that was generated. Likewise, the direction perpendicular to this plane is a [0001] direction. e) Photograph of a mag wheel – a lightweight auto wheel made of magnesium.
WHY STUDY The Structure of Crystalline Solids?
Describe the difference in atomic/molecular structure between crystalline and noncrystalline
Draw unit cells for face-centered cubic, body- centered cubic, and hexagonal close-packed
Derive the relationships between unit cell edge length and atomic radius for face-centered cubic
Compute the densities for metals having face- centered cubic and body-centered cubic crystal
Given three direction index integers, sketch the direction corresponding to these indices within a
Specify the Miller indices for a plane that has been drawn within a unit cell
Describe how face-centered cubic and hexagonal close-packed crystal structures may be generated
Distinguish between single crystals and poly- crystalline materials
- INTRODUCTION
- FUNDAMENTAL CONCEPTS
- UNIT CELLS
- Metallic Crystal Structures • 51 chosen to represent the symmetry of the crystal structure, wherein all the atom positions
- METALLIC CRYSTAL STRUCTURES
- Metallic Crystal Structures • 53
- Polymorphism and Allotropy • 57
- DENSITY COMPUTATIONS
- POLYMORPHISM AND ALLOTROPY
- Crystal Systems • 59
- CRYSTAL SYSTEMS
- Point Coordinates • 61
- POINT COORDINATES
- Point Coordinates • 63
Both the total atom and unit cell volumes can be calculated in terms of the atomic radius R. Specify the indices for all the numbered points of the unit cell in the illustration on the next page.
The coordinates of two points that lie on the direction vector (referenced to the coordinate system) are determined—for example, for the vector tail, point
If necessary, these three numbers are multiplied or divided by a common factor to reduce them to the smallest integer values
- CRYSTALLOGRAPHIC DIRECTIONS
- Crystallographic Directions • 65
- Crystallographic Directions • 67
- Crystallographic Directions • 69
Conversion from the three-index system (using the coordinate axes a1–a2–z of Figure 3.8b) to the four-index system as. The first thing we need to do is determine the indices U, V and W for the vector referred to in the three-axis scheme shown in the sketch; this is possible using equations 3.12a to 3.12c.
If the plane passes through the selected origin, either another parallel plane must be constructed within the unit cell by an appropriate translation, or a new origin
Again, the unit cell is the basis with the three-axis coordinate system as shown in Figure 3.5. If the plane passes through the selected origin, either another parallel plane must be constructed in the unit cell by an appropriate translation or a new origin.
At this point, the crystallographic plane either intersects or parallels each of the three axes. The coordinate for the intersection of the crystallographic plane with each of
If necessary, these three numbers are changed to the set of smallest integers by multiplication or by division by a common factor. 10
- CRYSTALLOGRAPHIC PLANES
- Crystallographic Planes • 71
- Crystallographic Planes • 73
- Crystallographic Planes • 75
- LINEAR AND PLANAR DENSITIES
- Close-Packed Crystal Structures • 77
- CLOSE-PACKED CRYSTAL STRUCTURES
- Polycrystalline Materials • 79
- SINGLE CRYSTALS
- POLYCRYSTALLINE MATERIALS
- ANISOTROPY
- X-RAY DIFFRACTION: DETERMINATION OF CRYSTAL STRUCTURES
On the unit cell shown in sketch (b) the locations of the intersections for this plane are noted. If one of the indices is zero [as in (110)], the plane will be a parallelogram, with two sides that coincide with opposite unit cell edges (or edges of adjacent unit cells) (according to Figure 3.10b).
Ray Diffraction and Bragg’s Law
- Noncrystalline Solids • 87
- NONCRYSTALLINE SOLIDS
- Calculate the equilibrium number of vacancies in a material at some specified temperature, given
- Name the two types of solid solutions and provide a brief written definition and/or
- For each of edge, screw, and mixed dislocations
- Describe the atomic structure within the vicinity of (a) a grain boundary and (b) a twin boundary
- INTRODUCTION
- VACANCIES AND SELF-INTERSTITIALS
The magnitude of the distance between two adjacent and parallel planes of atoms (i.e. the interplanar spacing dhkl) is a function of the Miller indices (h, k and l) as well as the lattice parameter(s). Concept check 3.3 For cubic crystals, as values of the planar indices h, k and l increase, the distance between adjacent and parallel planes (i.e. the interplanar spacing) increases or decreases.
WHY STUDY Imperfections in Solids?
This problem can be solved by using Equation 4.1; however, it is first necessary to determine the value of NCu - the number of atomic sites per cubic meter for copper, from its atomic weight ACu, its density 𝜌 and Avogadro's number NA according. The present discussion is about the idea of a solid solution; treatment of the formation of a new phase is deferred to Chapter 9.
IMPURITIES IN SOLIDS
A solid solution is formed when the crystal structure is maintained when the dissolved atoms are added to the host material and no new structures are formed. A solid solution is also compositionally homogeneous; the impurity atoms are randomly and uniformly distributed in the solid.
The drawing shows atoms on the (100) plane of a BCC unit cell; the large circles represent the host atoms—the small circle represents an interstitial atom positioned in an octahedral site on the cube edge. On this drawing, the unit cell edge length is recorded—the distance between the centers of the corner atoms—which, from Equation 3.4, is equal to.
SPECIFICATION OF COMPOSITION
The two most common ways to specify composition are weight (or mass) percent and atom percent. Sometimes it is necessary to convert from one composition scheme to another - for example, from weight percent to atom percent.
This is sometimes called the dislocation line, which for the edge dislocation in Figure 4.4 is perpendicular to the plane of the face. Sometimes the edge dislocation in Figure 4.4 is represented by the symbol ⊥, which also indicates the position of the dislocation line.
DISLOCATIONS—LINEAR DEFECTS
This is called an edge dislocation; is a linear error centered on a line defined along the end of an additional half-plane of atoms. An additional half-plane of atoms, which is included in the lower part of the crystal, can also form an edge dislocation; its label is a.
Most dislocations found in crystalline materials are probably neither pure edge nor pure screw, but exhibit components of both types; these are called mixed dislocations. For regions in between where there is curvature in the dislocation line, the character is mixed edge and screw.
INTERFACIAL DEFECTS
When this orientation mismatch is small, on the order of a few degrees, the term small (or small) angle grain boundary is used. A simple small-angle grain boundary is formed when edge dislocations are aligned in the manner shown in Figure 4.9.
Individual atoms are resolved in this micrograph, as well as some of the defects shown in Figure 4.11. Annealing twins can be observed in the photomicrograph of the polycrystalline brass sample shown in Figure 4.14c.
BULK OR VOLUME DEFECTS
ATOMIC VIBRATIONS
Sometimes it is necessary or desirable to investigate the structural elements and defects that affect the properties of materials. Relatively large grains with different textures are clearly visible on the surface of the sectioned copper ingot shown in Figure 4.13.
BASIC CONCEPTS OF MICROSCOPY
For example, the shape and average size or diameter of the grains of a polycrystalline sample are important structural properties. Microscopic examination is an extremely useful tool for the examination and characterization of materials.
MICROSCOPIC TECHNIQUES
An image of the structure being examined is formed using electron beams instead of light radiation. High magnifications and resolving powers of these microscopes are consequences of the short wavelengths of electron beams.
The useful dimensional resolution ranges for the several microscopic techniques discussed in this chapter (plus the unaided eye) are presented in the bar chart in Figure 4.16b. Bar chart showing the useful resolution ranges for four microscopic techniques discussed in this chapter, in addition to the naked eye.
GRAIN-SIZE DETERMINATION
Consequently, the number of grains per unit area increases with the square of the increase in magnification. In Figure 4.15b, for example, the scale is located in the lower right corner of the micrograph; his.
Measure the length of the scale bar in millimeters using a ruler
In addition, the inclusion of the (100M)2term takes advantage of the fact that, while magnification is a length parameter, area is expressed in terms of length units squared. Sometimes magnification is specified in the micrograph legend (eg, "60×" for Figure 4.14b); this means the micrograph represents a 60 times magnification of the sample in real space.
- Grain-Size Determination • 117
An edge can be thought of in terms of the lattice strain along the end of an extra half-plane of atoms. The "case" appears as the dark outer edge of that segment of the gear that has been cut.
Name and describe the two atomic mechanisms of diffusion
- INTRODUCTION
- Diffusion Mechanisms • 123
- DIFFUSION MECHANISMS
- FICK’S FIRST LAW
- Fick’s First Law • 125
- FICK’S SECOND LAW—NONSTEADY-STATE DIFFUSION
Fick's first law can be applied to the diffusion of atoms of a gas through a thin metal plate for which the concentrations (or pressures) of the diffusing species on both surfaces of the plate are kept constant, a situation shown schematically in Figure 5.3a. Most practical diffusion situations are non-steady-state—that is, the diffusion flux and concentration gradient at a particular point in a solid vary with time, resulting in a net accumulation or depletion of the diffusing species.
Often, the source of the diffusion species is a gas phase whose partial pressure is maintained at a constant value. Before diffusion, any solute atom in the solid is uniformly distributed with the concentration of C0.
The value of x at the surface is zero and increases with distance into the solid
If the diffusion coefficient is independent of what is commonly known as Fick's second law, it is used.
The time is taken to be zero the instant before the diffusion process begins
- FACTORS THAT INFLUENCE DIFFUSION
- Factors That Influence Diffusion • 131
- Factors That Influence Diffusion • 133
- Diffusion in Semiconducting Materials • 135 Using an interpolation technique as demonstrated in Example Problem 5.2 and the data presented
- DIFFUSION IN SEMICONDUCTING MATERIALS 7
- OTHER DIFFUSION PATHS
The magnitude of the diffusion coefficient D is indicative of the rate at which atoms diffuse. However, before this is possible, D must be calculated at the temperature of the running-in treatment [Dd at 1100 °C (1373 K)].
WHY STUDY The Mechanical Properties of Metals?
Define engineering stress and engineering strain
It is the job of engineers to understand how various mechanical properties are measured and what these properties represent; they may be required to design structures/components using predetermined materials such that unacceptable levels of deformation and/or failure. In Design Examples 6.1 and 6.2 we presented two typical types of design protocols; these examples demonstrate, respectively, a procedure used to design a tensile testing apparatus and how the material requirements for a cylindrical tube under pressure can be determined.
State Hooke’s law and note the conditions under which it is valid
Define Poisson’s ratio
Given an engineering stress–strain diagram, determine (a) the modulus of elasticity,
For the tensile deformation of a ductile cylindrical specimen, describe changes in specimen profile to
Compute ductility in terms of both percentage elongation and percentage reduction of area for
Give brief definitions of and the units for modulus of resilience and toughness (static)
For a specimen being loaded in tension, given the applied load, the instantaneous cross-
Name the two most common hardness-testing techniques; note two differences between
Compute the working stress for a ductile material
- INTRODUCTION
- CONCEPTS OF STRESS AND STRAIN
- Concepts of Stress and Strain • 145
- Concepts of Stress and Strain • 147
- STRESS–STRAIN BEHAVIOR
- Stress–Strain Behavior • 149
- Elastic Properties of Materials • 151
- ANELASTICITY
- ELASTIC PROPERTIES OF MATERIALS
- Elastic Properties of Materials • 153
- TENSILE PROPERTIES
- Tensile Properties • 157
- Tensile Properties • 159
- True Stress and Strain • 161 For the static (low strain rate) situation, a measure of toughness in metals
- TRUE STRESS AND STRAIN
- True Stress and Strain • 163
- ELASTIC RECOVERY AFTER PLASTIC DEFORMATION
- Hardness • 165
- COMPRESSIVE, SHEAR, AND TORSIONAL DEFORMATIONS
As shown in the stress-strain diagram (Figure 6.5), the application of the load corresponds to movement from the origin up and along a straight line. Elasticity units are the product of units from each of the two axes of the stress-strain graph.
They are simple and inexpensive—typically, no special specimen need be prepared, and the testing apparatus is relatively inexpensive
The resulting stress-strain behavior in the plastic region is similar to the tensile counterpart (Figure 6.10a: yield and the associated curvature). They are simple and inexpensive - typically no special sample preparation is required, and the test apparatus is relatively inexpensive.
The test is nondestructive—the specimen is neither fractured nor excessively deformed; a small indentation is the only deformation
Of course, metals can experience plastic deformation under the influence of applied compressive, shear and torsional loads. The depth or size of the resulting indentation is measured and related to the hardness number; the softer the material, the larger and deeper the indentation and the lower the value of the hardness index.
Other mechanical properties often may be estimated from hardness data, such as tensile strength (see Figure 6.19)
- HARDNESS
- Variability of Material Properties • 171
- VARIABILITY OF MATERIAL PROPERTIES
- Design/Safety Factors • 173 bars (short horizontal lines) situated above and below the data point symbol and
- DESIGN/SAFETY FACTORS
- Design/Safety Factors • 175
The upper error bar is located at a value of the mean value plus the standard deviation (TS+s), and the lower error bar corresponds to the mean minus the standard deviation (TS−s). The data point corresponds to the average value of the tensile strength (TS); error bars indicating the degree of dispersion correspond to the mean value plus and minus the standard deviation (TS±s).
WHY STUDY Dislocations and Strengthening Mechanisms?
Describe edge and screw dislocation motion from an atomic perspective
Describe how plastic deformation occurs by the motion of edge and screw dislocations in
Define slip system and cite one example
Describe how the grain structure of a poly- crystalline metal is altered when it is plastically
Explain how grain boundaries impede dislocation motion and why a metal having small grains is
Describe and explain solid-solution strengthen- ing for substitutional impurity atoms in terms of
Describe and explain the phenomenon of strain hardening (or cold working) in terms of
Describe recrystallization in terms of both the alteration of microstructure and mechanical
Describe the phenomenon of grain growth from both macroscopic and atomic perspectives
- INTRODUCTION
