Types of Materials

1. Types of Materials • Metals: • Strong, ductile • high thermal & electrical conductivity • opaque • Polymers/plastics: Covalent bonding  sharing of e’s • Soft, ductile, low strength, low density • thermal & electrical insulators • Optically translucent or transparent. • Ceramics: ionic bonding (refractory) – compounds of metallic & non-metallic elements (oxides, carbides, nitrides, sulfides) • Brittle, glassy, elastic • non-conducting (insulators)

2. Material Density

3. Material Stiffness

4. Material Resistance to Fracture

5. Material Electrical Conductivity

6. The Materials Selection Process Processes Structure Shape Composition Mechanical Electrical Thermal Optical Etc. Materials Properties Environment Load Applications Functions

7. Structure, Processing, & Properties (d) 30mm (c) (b) (a) 4mm 30mm 30mm • Properties depend on structure ex: hardness vs structure of steel Steel with 0.4 wt% C d) Martensite c) Martensite (tempered at 371 C) b) Fine pearlite a) Spheroidite 6 00 5 00 4 00 Hardness (BHN) 3 00 2 00 100 0.01 0.1 1 10 100 1000 Cooling Rate (ºC/s) • Processing can change structure ex: structure vs cooling rate of steel

8. 6 5 Cu + 3.32 at%Ni 4 Cu + 2.16 at%Ni Resistivity, r deformed Cu + 1.12 at%Ni 3 (10-8 Ohm-m) 2 Cu + 1.12 at%Ni 1 “Pure” Cu 0 -200 -100 0 T (°C) ELECTRICAL • Electrical Resistivity of Copper: • Adding “impurity” atoms to Cu increases resistivity. • Deforming Cu increases resistivity.

9. 400 300 (W/m-K) 200 Thermal Conductivity 100 0 0 10 20 30 40 Composition (wt% Zinc) 100mm THERMAL • Space Shuttle Tiles: --Silica fiber insulation offers low heat conduction. • Thermal Conductivity of Copper: --It decreases when you add zinc!

10. Fe+3%Si Fe Magnetization Magnetic Field MAGNETIC • Magnetic Storage: --Recording medium is magnetized by recording head. • Magnetic Permeability vs. Composition: --Adding 3 atomic % Si makes Fe a better recording medium!

11. OPTICAL polycrystal: low porosity polycrystal: high porosity single crystal • Transmittance: --Aluminum oxide may be transparent, translucent, or opaque depending on the material structure.

12. -8 10 “as-is” “held at 160ºC for 1 hr crack speed (m/s) before testing” -10 10 Alloy 7178 tested in saturated aqueous NaCl solution at 23ºC increasing load 4mm DETERIORATIVE • Stress & Saltwater... --causes cracks! • Heat treatment: slows crack speed in salt water! --material: 7150-T651 Al "alloy" (Zn,Cu,Mg,Zr)

13. Properties From Bonding: Tm Energy r r o r Energy smaller Tm unstretched length larger Tm r o r Eo = “bond energy” • Bond length, r • Melting Temperature, Tm • Bond energy, Eo Tm is larger if Eo is larger.

14. Properties From Bonding : a length, L o unheated, T 1 D L heated, T 2 r o Energy unstretched length r Larger a Eo Eo Smaller a • Coefficient of thermal expansion, a coeff. thermal expansion D L a = ( T - T ) 2 1 L o • a ~ symmetry at ro a is larger if Eo is smaller.

15. Summary: Primary Bonds secondary bonding Ceramics Large bond energy large Tm large E small a (Ionic & covalent bonding): Metals Variable bond energy moderate Tm moderate E moderate a (Metallic bonding): Polymers Secondary bonding dominates small Tm small E large a (Covalent & Secondary):

16. Brief of Metal

17. The Periodic Table • Columns: Similar Valence Structure H He Li Be O F Ne Na Mg S Cl Ar K Ca Sc Se Kr Rb Sr Y Te I Xe Cs Ba Po At Rn Fr Ra

18. Energy and Packing Energy typical neighbor bond length typical neighbor r bond energy • Dense, ordered packing Energy typical neighbor bond length r typical neighbor bond energy • Non dense, random packing Dense, ordered packed structures tend to have lower energies.

19. Materials and Packing Crystalline materials... • atoms pack in periodic, 3D arrays • typical of: -metals -many ceramics -some polymers crystalline SiO2 Si Oxygen Noncrystalline materials... • atoms have no periodic packing • occurs for: -complex structures -rapid cooling "Amorphous" = Noncrystalline noncrystalline SiO2

20. Types of Imperfections Line defects • Dislocations Area defects • Grain Boundaries • Vacancy atoms • Interstitial atoms • Substitutional atoms Point defects

21. Point Defects Vacancy distortion of planes self- interstitial distortion of planes • Vacancies: -vacant atomic sites in a structure. • Self-Interstitials: -"extra" atoms positioned between atomic sites.

22. Point Defects in Alloys Two outcomes if impurity (B) added to host (A): • Solid solution of B in A (i.e., random dist. of point defects) OR Substitutional solid soln. (e.g., Cu in Ni) Interstitial solid soln. (e.g., C in Fe) • Solid solution of B in A plus a new phase (usually for a larger amount of B) Second phase particle --different composition --often different structure.

23. Line Defects Dislocations: • are line defects, • slip between crystal planes result when dislocations move, • produce permanent (plastic) deformation. Schematic of Zinc (HCP): • before deformation • after tensile elongation slip steps

24. Imperfections in Solids Edge Dislocation

25. Imperfections in Solids Screw Dislocation Screw Dislocation b Dislocation line (b) Burgers vector b (a)

26. Mixed Edge Screw Edge, Screw, and Mixed Dislocations

27. Dislocations & Crystal Structures • Structure: close-packed planes & directions are preferred. view onto two close-packed planes. close-packed directions close-packed plane (bottom) close-packed plane (top) • Comparison among crystal structures: HCP: few slip systems/directions; FCC: many slip systems/directions; BCC: the most slip systems/directions • Specimens that were tensile tested. Mg (HCP) tensile direction Al (FCC)

28. Planar Defects in Solids • External Surfaces • The most obvious • Grain Boundary • Different crystal • orientation between • grains • twin boundary (plane) • Essentially a reflection of atom positions across the twin plane. • Stacking faults • For FCC metals an error in ABCABC packing sequence • Ex: ABCABABC • Phase boundary • In multiphase materials

29. Polycrystalline Materials Grain Boundaries • regions between crystals • transition from lattice of one region to that of the other • slightly disordered • low density in grain boundaries • high mobility • high diffusivity • high chemical reactivity