Industrial Materials

Allotropic

different crystal structures at different temperatures

Titanium Properties

resistant to corrosion, high specific strength, good high temp properties

6th reason to alloy a metal

Solid-solution strengthen the metal

Alpha phase stabilizers

raises transition temperature, results in 100% alpha microstructure at RT

Beta phase stabilizers

Lowers transition temp, results in either beta + alpha or 100% beta microstructure at RT

3 ways to strength Ti alloys

solid-solution strengthen, quench to form martensite from Beta phase, stabilize the beta phase so its present at RT

Solid-solution strengthening

adding in elements, such as Al or Sn

Intermetallic Compounds

ordered solid state of 2+ metallic elements, resist dislocations, hard & brittle

Ni-based super alloys produce what kind of precipitates

coherent

Ceramics

ordered compound consisting of metallic & non-metallic atoms

Ceramic bonds

ionic or covalent

AX ceramics

1:1 relationship, FCC or BCC

3 types of AX ceramics

NaCl/Rock salt, zinc blend, cesium chloride

A atom

larger atom, sits in larger crystal sites

X atom

smaller atom, sits in interstitial sites

NaCl rock salt structure

A-Cl, X-Na, sits in octahedral sites, forms a stretched FCC unit cell

Zinc Blend structure

A-S, X-Zn, sits in tetrahedral sites, forms a more abstract crystal structure

Cesium chloride structure

BCC unit cell, cesium atom sits in the centre of the body

Corundum structure (Al2O3)

O occupies HCP arrangment, Al occupy some octahedral sites leaving some vacent

Crystalline SiO2

quartz, long-range atomic order, not n AX crystal

Adding Na2O to SiO2

prevents formation of crystalline SiO2, makes a glass structure

Window Glass properties

non-crystalline, very weak, low melting temp

Glass Transition Temperature

defects move rapidly & material behaves in a viscous manner

Tg = Tmelt

For crystalline structures due to strong interatomic bonds

What is a viscous solid?

a solid where stress is a function of strain rate

All non-crystalline ceramics are…

Non-equilibrium structures

Solid-state sintering

diffusion-bonding used for fabrication, used as crystalline ceramics have a high Tg to allow for fabrication

2 Problems with Sintering

takes a long time to completely sinter powders, cannot get rid of all the porosity

3 main ingredients of traditional ceramics

Clay, water, crystalline powders

Benefits of traditional Ceramics

non-crystalline ceramic glass melts and covers non-melted crystalline ceramic powders binding them together, results in almost zero porosity

Cermets

composites consisting of crystalline ceramic powders imbedded in a crystalline metal binder

What is a polymer?

a material made of long molecules

degree of polymerization

# of monomers within polymer

Thermoplastic Polymers

long polymer molecules have no crosslinking

Thermosetting Polymers

long polymers have heavy crosslinking

Elastomers

Long polymer molecules have crosslinking in some locations

Functionality of a Monomer

number of sites at which a new molecule can be attached

Linear Polymers

1-dimensional bonding, units are joined end to end to form a single chain

Branched Polymers

branches extend from main molecular chain, don’t attach to neighboring molecules

Cross-linked polymers

molecular chains are joined together, high strength

Polymers get their strength from

mechanical interlocking between tangled molecules

Addition Polymerization

exposes ethylene gas to high pressure to weaken atomic bonding & add catalyst molecule R

Methods for ending polymerization process

Combination & Disproportionation

Combination

Two reactive ends of molecules join to remove dangling bonds

Disproportionation

donating one hydrogen atom from one molecule to another

How to increase strength of a polymer

Increase length of a molecule, increase size of side groups, align side groups, mix polymers, increase cross-linking

Length of molecules (Degree of Polymerization & Molecular weight)

long molecules require more energy to untangle, increasing the strength

Size of Side Groups

large side groups make it difficult to untangle molecules, increasing strength of polymers

Polymer Branching

Branching prevents molecules from packing close together, increased branching decreases strength

Isotactic

side groups are on one side of main chain

Syndiotactic

Side groups alternate in either side of main chain

Atactic

Side groups are randomly oriented around main chain

Side group alignment with largest strength

Isotactic

Tacticity (molecular configuration)

orientation of side groups within the polymer

Copolymerization

mixing repeat units together during polymerization, results in a hybrid of mechanical properties

Crystallization of polymers

fabricating a polymer with non-tangled molecules, polymers will be folded back upon themselves, high density & strength

4 types of copolymers

Alternating, Random, Block, Grafted

Copolymer

similar to a solid-solution alloy

Blended Polymer

similar to a two-phase alloy

If strength increase…

ductility decrease

Ferrous alloys

any alloy with iron

Principal ore used in production of iron

Hematite, Fe2O3

Raw materials used in irom-making

Coke, Limestone, Hot gases

Purpose of Coke in iron-making

Supplies heat for chemical reactions, produces CO to reduce iron ore

Purpose of Limestone in iron-making

Reacts with impurities to create a slag which is scraped off the top

Purpose of Hot Gases in iron-making

Used to burn coke, generate heat & reduce iron ore

Negative effects of current iron-making process

responsible for 7% of CO2 emissions, 1.5 tonnes of CO2 for 1 ton of iron

Purpose of conventional steel making

lowers carbon content of pig iron, adds alloy elements, creates useful solid product

Basic Oxygen Furnace

chamber that cannot generate its own heat, requires a supply of molten iron, pumps pure oxygen through pig iron to reduce carbon content

Electric Arc Furnace

heat & melt steel, uses scrap iron/steel, more expensive than a BOF

Direct reduction process

pure H2 or CH4 gas is used to reduce iron ore, drastically slows process & decreases amount of CO2 produced

5 main reasons to alloy steel

React with impurities, lower surface energy, react with carbon to form carbides, improve corrosion resistance, slow speed of phase transformations

3 reasons to add Si to steel

react with dissolved oxygen to prevent weakening of grain boundaries, lower surface energy making it more castable, promote formation for graphite flakes

TRIP steel

Austenite microstructure at room temp, trips to martensite when stress is applied (at room temp)

Properties of Martensitic Steel

high strength, low ductility, high wear resistance

Stainless Steel

Cr>11wt%, Cr has a high affinity for steel forming a thin layer when exposed to air

Why is nickel added to steel

Ni stabilizes austenite phase, making it possible for austenite phase at room temp

Types of stainless steel (lowest yield strength to highest yield strength)

Austenitic, Ferritic, Martensitic, Precipitation Hardened

How is sensitization caused?

chromium reacts with carbon at 400-800 C, causes areas of chromium depletion at grain boundaries, creating grain boundary corrosion

How to solve sensitization?

use a low carbon steel (no carbon = no carbides), Solution treat to eliminate depletion zones & prevent reforming carbides, Stabilize by alloying elements to react with carbides faster than Cr does

Types of Cast iron

Grey, Ductile, White, malleable

Grey cast iron

3 wt% Si breaks Fe3C to form graphite flakes which results is dampened vibrations, increased thermal conductivity, reduce shrinkage during solidification

Ductile cast iron

0.05% Mg is added to make graphite flakes nodular, makes corrosion visible (manhole cover)

White Cast Iron

1 wt% Si only forms graphite flakes when slowly cooled, outer is cooled fast, inner is cooled slow resulting in a hard outer & softer inner that absorbs shock well, ideal for pulleys

Malleable cast iron

1 wt% Si, formed from white cast iron when heated to 800-900 C for long periods of time, graphite clusters form

Carbon Content of cast iron

2-4.5 wt% carbon

Equilibrium Phase Diagrams

graphical representation of phases present in a metal alloy system

Eutectic Reactions

Liquid → two distinctly different solid phases, result in parallel plate microstructure

Eutectoid Reaction

Solid → two distinctly different solid phases, results in parallel plate microstructure (pearlite)

Fast cooling/Quenching

doesn’t allow time for atoms to arrange into equilibrium locations, limits time for grain growth, increases yield strength

Bainite

occurs when insufficient time is given for diffusion , consists of straight needles of Fe3C surrounded by ferrite matrix

Martensite

hardest steel phase, results in a stretched BCC unit cell called a BCT, occurs when steel is rapidly cooled from austenite

Isothermal Annealing Process

heat to a single solid phase state, quench quickly to a intermediate temp, hold at intermediate temp for a predetermined amount of time to form desired precipitate non-equilibrium microstructure

Quench & Tempering process

heat to a single solid phase, quench to room temp forming a supersatured single phase, reheat/temper at an elevated temp within two phase region to grow tiny precipitates

Coherent Precipitates

atom planes are continuous through matrix & precipitate, ideal as it imparts max elastic strain

4 Requirements for age hardening

alloy must be capable of being heated to single solid phase, alloy must be quenchable to supersaturated phase at room temp, must form a coherent 2nd phase when aged, matrix phase must be softer than the coherent 2nd phase

Hexagonal Close-Packed (HCP)

stacking atoms in tetrahedral locations, ABABABAB

Face-Centered-Cubic (FCC)

stacking atoms in octahedral locations, ABCABCAB

Body-Centered-Cubic (BCC)

non-close packed atomic stacking, equal spacing between atoms, ABABABAB

Types of defects

Line (dislocations), Point (interstitial/substitutional), Surface (grain boundaries)