METALS POLYMERS CERAMICS GLASSES COMPOSITES AND ADVANCED MATERIALS

METALS, POLYMERS, CERAMICS, GLASSES, COMPOSITES AND ADVANCED MATERIALS

� Materials: Materials is defined as substances of which some thing is composed or made. From an engineering point of view, it covers almost all relevant situations. � Materials may be defined as substance of which something is composed or made. � We obtain materials from earth crust and atmosphere. � Examples : § Silicon and Iron constitute 27. 72 and 5. 00 percentage of weight of earths crust respectively. § Nitrogen and Oxygen constitute 78. 08 and 20. 95 percentage of dry air by volume respectively

CHAPTER 1: METALS

Metal Alloys : Applications and Processing � How are metal alloys classified and how are they used? � What are some of the common fabrication techniques? � How do properties vary throughout a piece of material that has been quenched, for example? � How can properties be modified by post heat treatment?

Metals have a crystalline structure in which the atoms are arranged in an orderly manner. � Metals are - good thermal and electrical conductors, - strong and ductile at room temperature, - good strength at high temperature. � Metals and alloys are divided into two classes - Ferrous – Steel, cast iron - Nonferrous – Copper, aluminum �

Taxonomy of Metals Metal Alloys Ferrous Steels <1. 4 wt%C Nonferrous Cast Irons 3 -4. 5 wt%C Microstructure: ferrite, graphite, cementite Cu Al Mg Ti

Steels

Refinement of Steel from Ore Coke Iron Ore gas refractory vessel layers of coke and iron ore air slag Molten iron Limestone BLAST FURNACE heat generation C+O 2 ®CO 2 reduction of iron ore to metal CO 2 + C ® 2 CO 3 CO + Fe 2 O 3 ® 2 Fe+3 CO 2 purification Ca. CO 3 ® Ca. O+CO 2 Ca. O + Si. O 2 + Al 2 O 3 ® slag

Ferrous Alloys Iron containing – Steels - cast irons Nomenclature AISI & SAE 10 xx Plain Carbon Steels 11 xx Plain Carbon Steels (resulfurized for machinability) 15 xx Mn (10 ~ 20%) 40 xx Mo (0. 20 ~ 0. 30%) 43 xx Ni (1. 65 - 2. 00%), Cr (0. 4 - 0. 90%), Mo (0. 2 - 0. 3%) 44 xx Mo (0. 5%) where xx is wt% C x 100 example: 1060 steel – plain carbon steel with 0. 60 wt% C Stainless Steel -- >11% Cr

Cast Iron � Ferrous alloys with > 2. 1 wt% �more commonly 3 - 4. 5 wt%C C � low melting (also brittle) so easiest to cast � Cementite graphite decomposes to ferrite + Fe 3 C 3 Fe ( ) + C (graphite) �generally a slow process

Types of Cast Iron Gray iron � graphite flakes � weak & brittle under tension � stronger under compression � excellent vibrational dampening � wear resistant Ductile iron � add Mg or Ce � graphite in nodules not flakes � matrix often pearlite - better ductility

Types of Cast Iron White iron � <1 wt% Si so harder but brittle � more cementite Malleable iron � heat treat at 800 -900ºC � graphite in rosettes � more ductile

Production of Cast Iron

Limitations of Ferrous Alloys 1) Relatively high density 2) Relatively low conductivity 3) Poor corrosion resistance

Nonferrous Alloys

Metal Fabrication � How do we fabricate metals? �Blacksmith - hammer (forged) �Molding - cast � Forming Operations �Rough stock formed to final shape Hot working • T high enough for recrystallization • Larger deformations vs. Cold working • well below Tm • work hardening • smaller deformations

Metal Fabrication Methods FORMING v v Drawing Forging Rolling Extrusion CASTING v v Sand Casting Investment Casting Die Casting Continuous Casting JOINING v Powder Metalurgy v Welding

FORMING • Forging (Hammering; Stamping) eg wrenches, crankshafts force die A 0 Ad blank force often at elev. T

• Drawing (rods, wire, tubing) die Ao die Ad tensile force die must be well lubricated & clean • Extrusion (rods, tubing) Ao force container ram billet die holder extrusion die ductile metals, e. g. Cu, Al (hot) container Ad

• Rolling (Hot or Cold Rolling) (I-beams, rails, sheet & plate) roll Ao roll Ad

CASTING q mold is filled with metal q metal melted in furnace, perhaps alloying q q elements added. Then cast in a mold most common, cheapest method gives good production of shapes weaker products, internal defects good option for brittle materials

• Sand Casting (large parts, e. g. , auto engine blocks) • trying to hold something that is hot • what will withstand >1600ºC? Sand molten metal • cheap - easy to mold => sand!!! • pack sand around form (pattern) of desired shape • Die Casting (high volume, low T alloys)

Investment Casting (low volume, complex shapes e. g. , jewelry, turbine blades) plaster die formed around wax prototype wax Investment Casting • pattern is made from paraffin. • mold made by encasing in plaster of paris • melt the wax & the hollow mold is left • pour in metal • Continuous Casting (simple slab shapes) molten solidified

Joining • Powder Metallurgy (materials w/low ductility) pressure • Welding (when one large part is impractical) filler metal (melted) base metal (melted) fused base metal heat area contact densify point contact at low T densification by diffusion at higher T unaffected piece 1 heat affected zone unaffected piece 2 • Heat affected zone: (region in which the microstructure has been changed).

Thermal Processing of Metals Annealling: Heat to Tanneal then cool slowly

Why Hardness Changes W/Position - The cooling rate varies with position.

Quenching Medium & Geometry - effect of quenching medium Medium air oil water Severity of Quench low moderate high Hardness low moderate high • Effect of geometry: When surface-to-volume ratio increases: --cooling rate increases --hardness increases Position center surface Cooling rate low high Hardness low high

Metal Alloy Crystal Stucture Alloys � substitutional alloys �can be ordered or disordered �disordered solid solution �ordered - periodic substitution example: Cu. Au FCC Cu Au

Metal Alloy Crystal Structure � Interstitial alloys (compounds) �one metal much larger than the other �smaller metal goes in ordered way into interstitial “holes” in the structure of larger metal �Ex: Cementite – Fe 3 C

Metal Alloy Crystal Stucture � Consider FCC structure --- what types of holes are there? Octahedron - octahedral site = OH Tetrahedron - tetrahedral site = TD

Metal Alloy Crystal Stucture � Interstitials such as H, N, B, C � FCC has 4 atoms per unit cell 4 OH sites 8 TD sites OH sites TD sites