THE NATURE OF MATERIALS

1. THE NATURE OF MATERIALS Atomic Structure and the Elements Bonding between Atoms and Molecules Crystalline Structures Noncrystalline (Amorphous) Structures Engineering Materials

2. Importance of Materials in Manufacturing Anunderstanding of materials is fundamental in the study ofmanufacturingprocesses. Manufacturing is a transformation process It is the material that is transformed And it is the behavior of the material when subjected to the forces, temperatures, and other parameters of the process that determines the success of the operation

3. Element Groupings Simple Model of Atomic Structure for Several Atoms The basic structural unit ofmatter is the atom.Each atom is composed of a positively chargednucleus, surroundedby a sufficientnumberofnegativelycharged electrons sothat the chargesare balanced. The number of electrons identifies the atomic number and the element of the atom. (a) Hydrogen, (b) helium, (c) fluorine, (d) neon, and (e) sodium

4. ChemicalSymbol • To represent a particular atom we use the symbolism: A= mass number Z = atomic number To represent an ion

5. Element Groupings-PeriodicTable The elements can be grouped into families and relationships established between and within the families by means of the Periodic Table Metals occupy the left and center portions of the table Nonmetals are on right Between them is a transition zone containing metalloids or semi‑metals

6. The Modern Periodic Table • There are more than 110 elements listed in the modern periodic table . Each box, or entry, in the table gives the chemical symbol, atomic number (Z), and atomic mass of an element (illustrated for iron). • The elements are placed in order of increasing atomic number, a property more responsible for the behavior of an element than is its atomic mass.

7. Metals Tend to Lose Electrons

8. Metallic Character • Metallic character is related to atomic radius and ionization energy. • Metallic character generally • increases from right to left across a period, and • increases from top to bottom in a group.

9. Nonmetals Tend to Gain Electrons

10. Nonmetals • Atoms of a nonmetal generally have larger numbers of electrons in their valence shell than do metals. • All nonmetals (except H and He) are p-block elements. • Many nonmetals tend to form negative ions. • Nonmetallic character generally • increasesfromleft-to-right • increases frombottom-to-top • on the periodic table • (the oppositeofmetallic character)

11. Metalloids • A heavy stepped diagonal line separates metals from nonmetals; some elements along this line are called metalloids. • Metalloids have properties of both metals and nonmetals.

12. The Modern Periodic Table

13. Bonding Between Atoms and Molecules Atoms are held together in molecules by various types of bonds Primary bonds- generally associated with formation of molecules Secondary bonds- generally associated with attraction between molecules Primary bonds are much stronger than secondary bonds

14. Primary Bonds Characterized by strong atom‑to‑atom attractions that involve exchange of valence electrons Following forms: Ionic Covalent Metallic

15. Atoms of one element give up their outer electron(s), which are in turn attracted to atoms of some other element to increase electron count in the outermost shell to eight Ionic Bonding

16. Formation of a Crystal of Sodium Chloride Na donates an electron to Cl … … and opposites attract. Sodium reacts violently in chlorine gas.

17. Animation: Reaction of NawithCl

18. Electrons are shared (as opposed to transferred) between atoms in their outermost shells Covalent Bonding

19. Two Examples of Covalent Bonding

20. Sharing of outer shell electrons by all atoms to form a general electron cloud that permeates the entire block Metallic Bonding

21. Secondary Bonds Primary bonds involve atom‑to‑atom attractive forces, Whereassecondary bonds involve attraction forces between molecules No transfer or sharing of electrons Bonds are weaker than primary bonds Three forms: Dipole forces London forces Hydrogen bonding

22. Arise in a molecule comprised of two atoms with equal and opposite electrical charges • Each molecule therefore forms a dipole that attracts other molecules 1.Dipole Forces

23. Opposites attract! Polar Induced Dipole Bonds

24. Attractive force between non-polar molecules, i.e., atoms in molecule do not form dipoles • However, due to rapid motion of electrons in orbit, temporary dipoles form when more electrons are on one side 2.London Forces

25. FluctuatingInducedDipoles (LondonForces) (1) At a given instant, electron density, even in a nonpolar molecule like this one, is not perfectly uniform.

26. FluctuatingInducedDipoles (LondonForces) (2) … the other end of the molecule is slightly (+). The region of (momentary) higher electron density attains a small (–) charge … When another nonpolar molecule approaches …

27. FluctuatingInducedDipoles (LondonForces) (3) … this molecule induces a tiny dipole moment … … in this molecule.

28. Occurs in molecules containing hydrogen atoms covalently bonded to another atom (e.g., H2O) • Since electrons to complete shell of hydrogen atom are aligned on one side of nucleus, opposite side has a net positive charge that attracts electrons in other molecules 3.Hydrogen Bonding

29. Hydrogen Bonds in Water

30. Atoms and molecules are the building blocks of a more macroscopic structure of matter When materials solidify from the molten state, they tend to close ranks and pack tightly, arranging themselves into one of two structures: • Crystalline • Noncrystalline Macroscopic Structures of Matter

31. Structure in which atoms are located at regular and recurring positions in three dimensions Unit cell - basic geometric grouping of atoms that is repeated • The pattern may be replicated millions of times within a given crystal • Crystallinestructure is the characteristic structure of virtually all metals, as well as many ceramics and some polymers Crystalline Structure

32. Crystal Structures • Thestructures of crystalsmust be describedthroughthree-dimensionalpatterns. • Latticeplanesintersecttoproducethree-dimensionalfigureshavingsixfacesarranged in threesets of parallelplanes. • Thespecialcasefor a lattice in whichtheplanesareequidistanceandperpendicular(intersecting at 90oangles). This is called a cubiclattice. • Forothercrystals, theappropriatelatticemayinvolveplanesthatare not equidistantorthatintersect at anglesotherthan 90o . • Inall, thereare seven possibilitiesforcrystallattices. TheCubicLattice Theintersection of perpendicularplanes is shaded in green - it is a cube. An endlesslattice can be generatedbysimplemovingof thegreencube in threeperpendiculardirections.

33. Three types of crystal structure: • body-centered cubic, • face-centered cubic, and • hexagonal close-packed Three Crystal Structures in Metals

34. Unit Cells in the Cubic Crystal System Unit cells in the cubic crystal system The space filling models in the bottom row show contacts between spheres (atoms). In the simple cubic cell, spheres come into contact along each edge. In the body centered cubic (bcc) cell, contacts of the spheres is along the cube diagonal. In the face centered cubic (fcc) cell, contact is along the diagonal of each face.

35. Hexagonal Close Packed (hcp) • Thehexagonalclosestpacked(hcp)crystalstructure • Theunitcell is not a cube. • Thehexagonalprismshowingparts of thesharedspheres at thecornersandthesinglesphere at thecenter of theunitcell.

36. Room temperature crystal structures for some of the common metals: Body‑centered cubic (BCC) Chromium, Iron, Molybdenum, Tungsten Face‑centered cubic (FCC) Aluminum, Copper, Gold, Lead, Silver, Nickel Hexagonal close‑packed (HCP) Magnesium, Titanium, Zinc Crystal Structures for Common Metals

37. A perfect crystal is sometimesdesirable to satisfy • aesthetic or engineering purposes. For instance, a perfect diamond is more valuable than one containing imperfections • There are various reasons why a crystal’s lattice structure • maynot be perfect. • Imperfections often arise due to inability of solidifying material to continue replication of unitcell, e.g., grain boundaries in metals. Imperfections (Defects) in Crystals

38. Imperfections can also be introduced purposely; e.g., addition of alloying ingredient in metal Types of defects: • point defects, • line defects, • surface defects Imperfections (Defects) in Crystals

39. HeatTreating Video

40. Imperfections in crystal structure involving either a single atom or a small number of atoms 1-Point Defects Point defects: (a) vacancy (boşluk), (b) ion‑pairvacancy (Schottkydefect), (c)interstitialcy (fazla atom), (d) displaced ion (Frenkel Defect). ( (c) diffusion occurs when a substitutional atom exchanges lattice positions with a vacancy )

41. A line defect is a connectedgroup of point defects that forms a line in the lattice structure Most important line defect is a dislocation, which can take two forms: a) Edge dislocation b) Screw dislocation 2-Line Defects

42. Edge of an extra plane of atoms that exists in the lattice a) Edge Dislocation

43. Spiral within the lattice structure wrapped around an imperfection line, like a screw wrapped around its axis b) Screw Dislocation

44. Imperfections that extend in two directions to form a boundary . • The surface is an interruption in the lattice structure. Surface boundaries can also lieinside the material. Examples: External: the surface of a crystalline object is an interruption in the lattice structure • Internal: grain boundaries are the best example of internal surfaceinterruptions. 3- Surface Defects

45. DEFORMATION IN METALLIC CRYSTALS When a crystal experiences a gradually increasing stress, it first deforms elastically. Ifthe force is removed, the lattice structure (and therefore the crystal) returns to its original shape. Elastic Strain Deformation of a crystal structure: (a) original lattice: (b) elastic deformation, no permanent change in positions of atoms

46. If the stress is higher than forces holding atoms in their lattice positions, then a permanent shape change occurs (plasticdeformation - slip) Plastic Strain Plastic deformation (slip), in which atoms in the crystal lattice structure are forced to move to new "homes“

47. Slip (kayma)involves the relativemovement of atoms on opposite sides of a plane in the lattice,calledthe slip plane. Effect of Dislocations on Strain(baskı, germe) Effect of dislocations in the lattice structure under stress. In the series of diagrams, themovement of the dislocation allows deformation to occur under a lower stress than in a perfect lattice.

48. Slip occurs many times over throughout the metal when subjected to a deforming load, thus causing it to exhibit its macroscopic behavior in the stress-strain relationship Dislocations are a good‑news‑bad‑news situation • Good news in manufacturing – the metal is easier to form • Bad news in design – the metal is not as strong as the designer would like Slip on a Macroscopic Scale

49. Twinning is a second way in which metal crystals plastically deform. Twinningcan bedefined as amechanismof plastic deformation in which atoms on one side of a plane (calledthe twinning plane) are shifted to form a mirror image (ayna hayali) of the other side of the plane. Twinning (ikiz oluşturma)

50. Twinning After • Before