1. Elements of Materials Science and Engineering ChE 210 Instructor: Dr. Ahmed Arafat, PhD Office : building 45 room 106 E-mail: akhamis@kau.edu.sa www.kau.edu.sa.akhamiswww.kau.edu.sa.akhamis  files

2. Book Elements of Materials Science and Engineering Sixth Edition Lawrence H. van Vlack

3. Chapters Chapter 1: Introduction to Materials Science and Engineering Chapter 2: Atomic Bonding and Coordination Chapter 3: Crystals (atomic order) Chapter 4: Disorder in solid phases Chapter 5: Phase Equilibria Chapter 6: Reaction rates Chapter 7: Microstructures Chapter 8: Deformation and Fracture Chapter 9: Shaping Strengthening and Toughening Processes

4. Grading Presence: = 5 % Major Exam I = 1 x 10% = 10 % Major Exam II = 1 x 15% = 15 % Quizzes: 2 x 5% = 10 % Laboratory = 20 % Final Exam=40 %

5. Introduction to Materials Science and Engineering Materials and civilization Material and Engineering Structure properties Performance Types of materials

6. Historical Perspective Historical Perspective Stone → Bronze → Iron → Advanced materials Beginning of the Material Science - People began to make tools from stone – Start of the Stone Age about two million years ago. Natural materials: stone, wood, clay, skins, etc. The Stone Age ended about 5000 years ago with introduction of Bronze in the Far East. Bronze is an alloy (a metal made up of more than one element), copper + < 25% of tin + other elements. Bronze: can be hammered or cast into a variety of shapes, can be made harder by alloying, corrode only slowly after a surface oxide film forms.

7. Historical The Iron Age began about 3000 years ago and continues today. Use of iron and steel, a stronger and cheaper material changed drastically daily life of a common person. Age of Advanced materials: throughout the Iron Age many new types of materials have been introduced (ceramic, semiconductors, polymers, composites…). Understanding of the relationship among structure, properties, processing, and performance of materials. Intelligent design of new materials.

8. Historical understanding the structure-composition-properties lead to a remarkable progress in properties of materials. e.g. the strength : density ratio of materials, resulted in a variety of new products, from dental materials to tennis racquets.

10. Materials and Civilization (1) Materials are integral part of human culture In the past: Stone, Bronze and Iron ages Role of Engineer: Adapting materials and energy to society’s needs The properties of materials depends on the internal structure To change the performance of materials, modification of the internal structure is required

11. Materials and Civilization (2) Human are able to make things: Objects tools, component systems This require materials to meet these purposes Anthropolgists and historians identified the early cultures by the most significant materials used then, e.g. Stone, the Bronze. and the Iron Ages of the past These days, are not limited to one predominant material. A lot of sophisticated materials-plastics, silicon, titanium, high- technology ceramics, optical fibers, and so on The age of technology.

12. Materials and Engineering (1) Engineer, design products and systems and monitor their use Every product is made of materials and energy is involved in production and in use. This is why all Engineers have to study materials science during their undergraduate study

13. Structure

14. Length-scales Angstrom = 1Å = 1/10,000,000,000 meter = 10 -10 m Nanometer = 10 nm = 1/1,000,000,000 meter = 10 -9 m Micrometer = 1µm = 1/1,000,000 meter = 10 -6 m Millimeter = 1mm = 1/1,000 meter = 10 -3 m Interatomic distance ~ a few Å A human hair is ~ 50 µm Elongated bumps that make up the data track on CD are ~ 0.5 µm wide, minimum 0.83 µm long, and 125 nm high

15. Properties

16. Types of Materials Metals: valence electrons are free moving, and spread in an 'electron sea' that "glues" the ions together. Strong, ductile, conduct electricity and heat well, are shiny if polished. Semiconductors: the bonding is covalent. Their electrical properties depend strongly on minute proportions of contaminants. Examples: Si, Ge, GaAs. Ceramics: composed of ions, and are bound by Coulomb forces. They are usually combinations of metals or semiconductors with oxygen, nitrogen or carbon, Hard, brittle, insulators. Examples: glass, porcelain. Polymers: are bound are covalent bonded or weak van der Waals bonded, based on C and H. They decompose at moderate temperatures (100 – 400 o C), and are lightweight. Examples: plastics rubber.

17. Types of Materials Metals: valence electrons are free moving, and spread in an 'electron sea' that "glues" the ions together. Strong, ductile, conduct electricity and heat well, are shiny if polished. Semiconductors: the bonding is covalent. Their electrical properties depend strongly on minute proportions of contaminants. Examples: Si, Ge, GaAs. Ceramics: composed of ions, and are bound by Coulomb forces. They are usually combinations of metals or semiconductors with oxygen, nitrogen or carbon, Hard, brittle, insulators. Examples: glass, porcelain. Polymers: are bound are covalent bonded or weak van der Waals bonded, based on C and H. They decompose at moderate temperatures (100 – 400 o C), and are lightweight. Examples: plastics rubber.

19. Engineering Properties of Materials Electrical resistance Electrical Conductivity Charge flux along voltage gradient (  ) ohm -1 = 1/R Thermal Conductivity Energy flux along thermal gradient (K) W/m* o C Resistivity Reciporical of electrical conductivity (  ), ohm * m

20. Engineering Properties of Materials Stress (s): Force per unit area, N/m 2 or MPa [psi] Strength (S): critical stress for failure, N/m 2 or MPa [psi] Strain (e) Dimensional response to stress, fraction or % Ductility: Elastic strain prior to fracture Elastic modulus:(E) ratio of stress/elastic strain N/m 2 MPa [psi] Hardness: Resistance to penetration Toughness: Energy absorbed prior to fracture

21. Structure ↔ Properties ↔ Performance Poorly available materials  rarely used Extensively used materials  iron, steel, paper, concrete, water, plastics. There extensive subdivision of all the above materials Materials must be modified in such a way that it can be easily used, e.g. gears

22. Example 1-2.1 A copper wire has a diameter of 0.9 mm. (a) what is the resistance of a 30 cm wire? (b) How many watts are expected if 1.5 volts dc are applied across 30 m of this wire? Solution  = 17 ohm.nm,

23. Example 1-2.2 Which part has a greater stress: (a) a rectangular aluminium bar of 24.6 mm x 30.7 mm cross-section, under a load of 7640 Kg, and therefore, a force of 75000 N or (b) a round steel bar whose cross-sectional diameter is 12.8 mm, under 5000 Kg load? Solution

24. Mechanical Behaviour A material changes in shape when forces are applied on. This change in dimensions is called deformation. Strain: is the amount of deformation per unit length. Stress: is the force per unit length. Energy is absorbed during deformation of a material because work must be done by applying force along the deformation distance. Strength: is the amount of stress required to cause the material to fail. Ductility: identifies the amount of strain at failure. Toughness: relates to the amount of energy absorbed by a material during failure. Since strength and ductility tend to be incompatible, the designer must often optimize between the two parameters.

25. a)non-ductile material with no plastic deformation e.g. Cast Iron Mechanical Behaviour b) Ductile material with yield point. e.g. Low carbon steel BS: Breaking Stength, YP: yield point and TS Tensile strength

26. Mechanical Behaviour Ductile material without marked yield point e.g. aluminium True stress-strain curve

27. Mechanical Behaviour Initially, strain is proportional to stress and shows reversible behaviour. i.e. When stress is removed the strain disappears. The modulus of elasticity (Young’s Modulus) is the ratio between the stress  and the reversible strain . E =  /  The units of young’s modulus is psi or pascals. The value of elastic modulus is a measure of the interatomic bonding forces and relates to the rigidity of engineering designs. at higher stresses, permanent displacement can occur among the atoms within a material. In this case much of the strain is not reversible when the applied stresses are removed. In contrast with previous (elastic) strain this is called plastic strain.

28. Mechanical Behaviour During the processing of materials plastic strain is needed while in product applications one has to design at stresses within the elastic range. Ductility may be expressed as elongation viz (L f – L o )/L o or  L/L o and is dimensionless. However, since elongation is commonly localized in the necked down area, the amount of elongation depends on the grain size. A second measure of ductility is reduction in area: (A o – A f )/A o or  A/A o at the point of fracture. This does not require gauge length. There is no exact correlation between the two.

29. Mechanical Behaviour Strength (and Hardness). The ability of a material to resist plastic deformation is called the yield strength (ys). This is calculated by dividing the force required to initiate the yield (first plastic deformation) by the cross-sectional area. In mild steel the yield strength is marked by a definite yield point is not well defined, the yield strength is defined as that stress required to produce 0.2% plastic offset.

30. Mechanical Behaviour The Tensile Strength (TS) Is calculated by dividing the maximum load by the original cross-sectional area. (while the true stress is based on the actual area). The engineer often uses nominal stress because he makes his calculation on the basis of original dimensions. Because the cross-sectional area of a ductile material may be reduced considerably before it breaks. The breaking strength (BS) may be less than the tensile strength.

31. Mechanical Behaviour Hardness is the resistance of a material to penetration of its surface. The hardness and strength are related so that for a wide range of metallic materials strength increases with hardness.

32. Mechanical Behaviour The Brinell Hardness Number (BHN) is a hardness index calculated from the area of penetration by a large identer. The Rockwell Hardness (R) is measured by the depth of penetration by a small identer. Toughness: is the measure of the energy to break the materials. H is force x distance and is expressed in Joules.

33. Mechanical Behaviour A ductile material with the same strength as a non-ductile (brittle) material will require more energy for breaking and will be tougher. There are several ways of measuring this quantity. Charpy and Izod are two examples. The shape of lost piece, method of applying the energy and geometry of stress concentrations are important.

34. True Stress-strain curve While nominal stress is defined as the force applied per unit area of the original cross-section of a test piece, this value does not indicate the real stress experienced by the material, because the cross-section of a test piece under increasing force decreases progressively. Therefore, the true stress in the material increases with strain continuously. A formula for the true strain may be derived as follows:

35. True Stress-strain curve For plastic deformation it is assumed that:

36. True Stress-strain curve The diagram below compares the nominal and true stress- strain curves