UNIT – I 3 Introduction Materials science, also commonly known as materials science and engineering, is an interdisciplinary field which deals with the discovery. Imperfections in Solids, Lecture Notes-Imperfections in Solids, PDF, kb of Materials, Lecture Notes-Corrosion and Degradation of Materials, PDF, MSE Introduction to the Science and Engineering of Materials Fall MSE - Section Notes in pdf format · Notes in pdf format, 4 slides per page .
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materials science as a new emerging science that encompasses physical metallurgy .. note how the increase in strength per unit density of materials correlates. Material Science Notes - Free download as Word Doc .doc), PDF File .pdf), Text File .txt) or read online for free. Engineering Class handwritten notes, exam notes, previous year questions, PDF free download.
Thus ingot casting, foundry methods, blast furnace extraction, and electrolytic extraction are all part of the required knowledge of a materials engineer.
Often the presence, absence, or variation of minute quantities of secondary elements and compounds in a bulk material will greatly affect the final properties of the materials produced.
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Thus, the extracting and purifying methods used to extract iron in a blast furnace can affect the quality of steel that is produced. Ceramics and glasses[ edit ] Main article: Ceramic Si3N4 ceramic bearing parts Another application of material science is the structures of ceramics and glass typically associated with the most brittle materials.
Bonding in ceramics and glasses uses covalent and ionic-covalent types with SiO2 silica or sand as a fundamental building block. Ceramics are as soft as clay or as hard as stone and concrete. Usually, they are crystalline in form. Most glasses contain a metal oxide fused with silica.
At high temperatures used to prepare glass, the material is a viscous liquid. The structure of glass forms into an amorphous state upon cooling. Windowpanes and eyeglasses are important examples. Fibers of glass are also available. Scratch resistant Corning Gorilla Glass is a well-known example of the application of materials science to drastically improve the properties of common components.
Diamond and carbon in its graphite form are considered to be ceramics. Engineering ceramics are known for their stiffness and stability under high temperatures, compression and electrical stress.
Alumina, silicon carbide , and tungsten carbide are made from a fine powder of their constituents in a process of sintering with a binder. Hot pressing provides higher density material. Chemical vapor deposition can place a film of a ceramic on another material.
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Cermets are ceramic particles containing some metals. Hence, semiconductors form the basis of the traditional computer.
This field also includes new areas of research such as superconducting materials, spintronics , metamaterials , etc. The study of these materials involves knowledge of materials science and solid-state physics or condensed matter physics. Computational materials science and engineering[ edit ] With continuing increases in computing power, simulating the behavior of materials has become possible.
This enables materials scientists to understand behavior and mechanisms, explain properties formerly poorly understood, and even to design new materials. Efforts surrounding Integrated computational materials engineering are now focusing on combining computational methods with experiments to drastically reduce the time and effort to optimize materials properties for a given application. This involves simulating materials at all length scales, using methods such as density functional theory , molecular dynamics , Monte Carlo algorithm , dislocation dynamics, Phase field models , Finite element method , and many more.
In industry[ edit ] Radical materials advances can drive the creation of new products or even new industries, but stable industries also employ materials scientists to make incremental improvements and troubleshoot issues with currently used materials. Industrial applications of materials science include materials design, cost-benefit tradeoffs in industrial production of materials, processing methods casting , rolling , welding , ion implantation , crystal growth , thin-film deposition , sintering , glassblowing , etc.
Besides material characterization, the material scientist or engineer also deals with extracting materials and converting them into useful forms. Thus ingot casting, foundry methods, blast furnace extraction, and electrolytic extraction are all part of the required knowledge of a materials engineer. Often the presence, absence, or variation of minute quantities of secondary elements and compounds in a bulk material will greatly affect the final properties of the materials produced.
Thus, the extracting and purifying methods used to extract iron in a blast furnace can affect the quality of steel that is produced. Ceramics and glasses[ edit ] Main article: Ceramic Si3N4 ceramic bearing parts Another application of material science is the structures of ceramics and glass typically associated with the most brittle materials. Bonding in ceramics and glasses uses covalent and ionic-covalent types with SiO2 silica or sand as a fundamental building block. Ceramics are as soft as clay or as hard as stone and concrete.
Usually, they are crystalline in form. Most glasses contain a metal oxide fused with silica. At high temperatures used to prepare glass, the material is a viscous liquid. This is more easily achieved when the atoms vibrate strongly, that is, at high temperatures. There is a difference between diffusion and net diffusion.
In a homogeneous material, atoms also diffuse but this motion is hard to detect. This is because atoms move randomly and there will be an equal number of atoms moving in one direction than in another. In inhomogeneous materials, the effect of diffusion is readily seen by a change in concentration with time.
In this case there is a net diffusion. Net diffusion occurs because, although all atoms are moving randomly, there are more atoms moving in regions where their concentration is higher. Steady state diffusion means that J does not depend on time. The concentration gradient is often called the driving force in diffusion but it is not a force in the mechanistic sense.
The minus sign in the equation means that diffusion is down the concentration gradient. Thus, atomic vibrations created by temperature assist diffusion. Also, smaller atoms diffuse more readily than big ones, and diffusion is faster in open lattices or in open directions. Short circuits are often unimportant because they constitute a negligible part of the total area of the material normal to the diffusion flux. Chapter Mechanical Properties of Metals 1.
Introduction Often materials are subject to forces loads when they are used. Mechanical engineers calculate those forces and material scientists how materials deform elongate, compress, twist or break as a function of applied load, time, temperature, and other conditions.
Materials scientists learn about these mechanical properties by testing materials. Results from the tests depend on the size and shape of material to be tested specimen , how it is held, and the way of performing the test. That is why we use common procedures, or standards, which are published by the ASTM.
Concepts of Stress and Strain To compare specimens of different sizes, the load is calculated per unit area, also called normalization to the area.
Force divided by area is called stress. In tension and compression tests, the relevant area is that perpendicular to the force. In shear or torsion tests, the area is perpendicular to the axis of rotation. There is a change in dimensions, or deformation elongation, DL as a result of a tensile or compressive stress.
To enable comparison with specimens of different length, the elongation is also normalized, this time to the length L. This is called strain, e.
One could divide force by the actual area, this is called true stress see Sec. For torsional or shear stresses, the deformation is the angle of twist, q Fig.
When the stress is removed, the material returns to the dimension it had before the load was applied. Valid for small strains except the case of rubbers. Deformation is reversible, non permanent Plastic deformation. When the stress is removed, the material does not return to its previous dimension but there is a permanent, irreversible deformation.
E is Young's modulus or modulus of elasticity. Elastic moduli measure the stiffness of the material. They are related to the second derivative of the interatomic potential, or the first derivative of the force vs.
By examining these curves we can tell which material has a higher modulus.
Due to thermal vibrations the elastic modulus decreases with temperature. E is large for ceramics stronger ionic bond and small for polymers weak covalent bond. Since the interatomic distances depend on direction in the crystal, E depends on direction i. For randomly oriented policrystals, E is isotropic. Anelasticity Here the behavior is elastic but not the stress-strain curve is not immediately reversible.
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It takes a while for the strain to return to zero. The effect is normally small for metals but can be significant for polymers. Elastic Properties of Materials Materials subject to tension shrink laterally. Those subject to compression, bulge. The ratio of lateral and axial strains is called the Poisson's ratio n. Tensile Properties Yield point. If the stress is too large, the strain deviates from being proportional to the stress.
The point at which this happens is the yield point because there the material yields, deforming permanently plastically. Yield stress. Hooke's law is not valid beyond the yield point.
The stress at the yield point is called yield stress, and is an important measure of the mechanical properties of materials. In practice, the yield stress is chosen as that causing a permanent strain of 0.
The yield stress measures the resistance to plastic deformation. The reason for plastic deformation, in normal materials, is not that the atomic bond is stretched beyond repair, but the motion of dislocations, which involves breaking and reforming bonds. Plastic deformation is caused by the motion of dislocations. Tensile strength. When stress continues in the plastic regime, the stress-strain passes through a maximum, called the tensile strength sTS , and then falls as the material starts to develop a neck and it finally breaks at the fracture point Fig.
Note that it is called strength, not stress, but the units are the same, MPa. For structural applications, the yield stress is usually a more important property than the tensile strength, since once the it is passed, the structure has deformed beyond acceptable limits. The ability to deform before braking. It is the opposite of brittleness. Ductility can be given either as percent maximum elongation emax or maximum area reduction. Capacity to absorb energy elastically.
The energy per unit volume is the area under the strain-stress curve in the elastic region. Ability to absorb energy up to fracture. The energy per unit volume is the total area under the strain-stress curve. It is measured by an impact test Ch. True Stress and Strain When one applies a constant tensile force the material will break after reaching the tensile strength. The material starts necking the transverse area decreases but the stress cannot increase beyond sTS.
The ratio of the force to the initial area, what we normally do, is called the engineering stress. If the ratio is to the actual area that changes with stress one obtains the true stress.
Elastic Recovery During Plastic Deformation If a material is taken beyond the yield point it is deformed plastically and the stress is then released, the material ends up with a permanent strain.
If the stress is reapplied, the material again responds elastically at the beginning up to a new yield point that is higher than the original yield point strain hardening, Ch. The amount of elastic strain that it will take before reaching the yield point is called elastic strain recovery Fig.
Compressive, Shear, and Torsional Deformation Compressive and shear stresses give similar behavior to tensile stresses, but in the case of compressive stresses there is no maximum in the s-e curve, since no necking occurs. Hardness Hardness is the resistance to plastic deformation e.
Thus, it is a measure of plastic deformation, as is the tensile strength, so they are well correlated. Historically, it was measured on an empirically scale, determined by the ability of a material to scratch another, diamond being the hardest and talc the softer.
Now we use standard tests, where a ball, or point is pressed into a material and the size of the dent is measured. There are a few different hardness tests: Rockwell, Brinell, Vickers, etc. They are popular because they are easy and non-destructive except for the small dent. Variability of Material Properties Tests do not produce exactly the same result because of variations in the test equipment, procedures, operator bias, specimen fabrication, etc.
But, even if all those parameters are controlled within strict limits, a variation remains in the materials, due to uncontrolled variations during fabrication, non homogenous composition and structure, etc. The measured mechanical properties will show scatter, which is often distributed in a Gaussian curve bell-shaped , that is characterized by the mean value and the standard deviation width. To take into account variability of properties, designers use, instead of an average value of, say, the tensile strength, the probability that the yield strength is above the minimum value tolerable.
Not tested: true stress-true stain relationships, details of the different types of hardness tests, but should know that hardness for a given material correlates with tensile strength. Variability of material properties Chapter 7. Introduction The key idea of the chapter is that plastic deformation is due to the motion of a large number of dislocations. The motion is called slip. Thus, the strength resistance to deformation can be improved by putting obstacles to slip.
Basic Concepts Dislocations can be edge dislocations, screw dislocations and exist in combination of the two Ch. Their motion slip occurs by sequential bond breaking and bond reforming Fig. The number of dislocations per unit volume is the dislocation density, in a plane they are measured per unit area. Characteristics of Dislocations There is strain around a dislocation which influences how they interact with other dislocations, impurities, etc.
There is compression near the extra plane higher atomic density and tension following the dislocation line Fig. When they are in the same plane, they repel if they have the same sign and annihilate if they have opposite signs leaving behind a perfect crystal. In general, when dislocations are close and their strain fields add to a larger value, they repel, because being close increases the potential energy it takes energy to strain a region of the material.Hibbeler Book If the ratio is to the actual area that changes with stress one obtains the true stress.
Surface atoms are not bonded to the maximum number of nearest neighbors and therefore in a higher energy state than the atoms at interior position. Composites made of different materials in intimate contact example: After reaching the desired temperature, the parts are held at that temperature for about 2 hours, then removed from the bath and cooled in still air.