Topic 2: Materials Flashcards
Metals
Good conductors of heat and electricity
Not transparent
lustrous
strong but able to be deformed
Ceramics
Godo insulators of electricity and heat
resistant to high temperatures
hard but brittle
Polymers
Large molecular structure
low density
flexible
Composites
Combination of materials from different groups.
Interstitial Solution
solute atoms are small in comparison to solvent atoms. Solute atoms occupy spaces present in the crystal lattice of the solvent
Substitutional Solution
Solute atoms take up positions normally occupied by atoms of solvent-> atoms swap or substitute themselves into the lattice. Solute and solvent atoms are same size.
Ordered- atoms occupy similar lattice positions in the structure
Disordered- substitution is random
Homogenous
composed of parts/elements that are the same kind-> single phase
Heterogenous
composed of parts/elements that are different kinds. Components don’t disperse uniformly.
Phase
A homogenous portion of a system-> uniform physical and chemical characteristics that can be physically seperated
Equilibrium
state of a system where the phase characteristics remain constant
Alloy
Material composed of at least two different elements
Main/parent/base metal
most important component in an alloy-> usually over 90% of the alloy material
Impurities
chemical substances that differ from the chemical composition of the material
Solid Solubility
the extent of a metal to be able to form a solid solution with another metal
States of matter
gas, liquid.solid
Solidification and Cystallisation
- Crystals start nucleation
- crystal growth
- grains form as crystals grow together
- Grain boundaries are formed
Complete solid solubility
Two elements re able to become one solution in the solid phase
Former when:
1. Metals have same crystal structure
2. atoms exhibit similar chemical characteristics and are similar in size
3. solid solutions are designated by alpha, beta and gamma.
Equilibrium cooling
cooling occurs slowly in which the phase equilibrium is maintained.
Non-Equilibrium cooling
Diffusion is used to readjust the composition of solid and liquid phases. During the cooling one metal is more abundant in the centre of the grains as the remaining liquid is richer in the other metal.
Cored Grains
Result of Non-Equilibrium/industrial cooling. One metal is more abundant in the centre of the grain.
Inverse Lever Rule
Used to calculate proportions of solid and liquid at a temperature.
To find the amount of solid measure the distance from composition to the liquidus
To find the amount of liquid measure the distance from the composition to the solidus.
Eutectic Mixtures
Formed in an alloy system when two solid phases separate simultaneously at a constant temperature from a single liquid phase.
The phase present in a eutectic mixture are alternating layers of the two pure metals.
solid+solid->liquid
Eutectoid Transformations
Occurs when an existing single solid phase breaks down into two separate phases which are mixed in the transformed alloy.
solid+solid->solid
Peritectic changes
During the solidification of a cooling alloy, the solid already formed may react with residual liquid to form another solid solution or compound between the first solid present and the liquid.
Complete solid insolubility
Contains a eutectic point to indicate the composition to the lowest melting point of alloying elements.
If the complete solid insolubility is in the solid state, the metals won’t mix and will remain separate->eutectic point
Eutectic point
point on phase diagram indicating chemical composition and temperature corresponding to the lowest melting point of alloying elements.
Eutectic Structure
alternating layers of two materials with eutectic composition-> Lamella
Partial Solid Solubility
Original materials mix to produce a new solid
Eutectoid point
point in aphase diagram indicating the chemical composition and temperature to the location where three solid phases co exist
Effect of carbon on steel
from the eutectoid composition
as the carbon content decreases, alpha ferrite increases-> causes increased ductility but less strength
as the carbon content increases, cementite increases-> causes increases mechanical strength but less ductility
Austenite
single phase solid solution
FCC Orientation
can contain up to 2% carbon
exists above eutectoid temperature of 727C
Austinite is denser and has larger holes that ferrite to dissolve more carbon
dense structure has more slip planes-> easily flattened
Ferrite
Single phase solid solution
BCC orientation
only exists above 1394C
More porous but holes are small-> can only dissolve up to 0.03% carbon
Soft, Ductile, low tensile strength
Cementite
Is the compound iron carbide
Contains 6.67% carbon
very hard, brittle, low tensile strength, high compressive strength
Pearlite
Is the eutectoid composition
Contains 0.77% carbon
Alternating bands of ferrite and cementite
Ledeburite
Mixture of 4.3% carbon
Eutectic mixture of austenite and cementite
Hypoeutectoid steel
contains less than 0.77% carbon
Consists of pearlite and ferrite at room temp
Hypereutectoid steel
contains more than 0.77% carbon
Consists of pearlite and cementite at room temp
Low carbon steel
0.07-0.15% carbon
Uses: Automobile body parts, wire, chains
Properties: soft, weak, cold workable, malleable, ductile, low tensile strength
Mild carbon steel
0.15-0.3% carbon
Uses: structural plates, brackets, bolts, stampings, forgings, seamless tubes, boiler plate, car wheels
Properties: doesn’t harden well when quenched, weldable, cold workable, strong, ductile, very tough
Medium carbon steel
0.3-0.6% carbon
Uses: forgings, Automotive components-> crankshafts, axels, gears, train rails, wheels, axles
Properties: can be hot or cold formed, suitable for forging and heat treatment, strong, ductile, tough
High carbon steel
0.6-1.25% carbon
Uses: Suspension, springs, wires, cutting tools, punches, dies, cables, industrial knives, wear plates
Properties: Heat treatable, Very strong, Very hard
Ultra-high carbon steel
1.25-2% carbon
Uses: High tempered non industrial knives, punches, ball bearings, roller bearings
Properties: high wear resistance, high impact resistance, very hard, very brittle, high compressive strength.
Quench Hardening
steel alloys are strengthened and hardened by cooling from high temperatures.
Tempering
method of heat treatment used on steel allows to achieve higher toughness but hardness is decreased. Also increases the ductility
Tempering is done by heating the hardened material to a temperature below the austenite eutectoid temperature.
Heating above the eutectoid temperature will destroy the hard martensite achieved from quenching
Thermoplastic plastics
made of lines of long chain molecules with few cross linkage
allows softening when heated so that they can be bent into different shapes and become stiff when cooled.
Thermosetting plastics
made of molecules that are heavily cross linked.
Creates a rigid structure that becomes permanently stiff and solid.
Polyethylene
Properties: tough, flexible, low density, very chemical and electrical resistant, non toxic, easily moulded, heat sealable. wide colour range
Uses: plastic containers, water pipes, cable insulation
Polypropylene
Properties: strong, tough, flexible, high impact resistance, high electrical, chemical, and heat resistance, medium density, easily moulded, chrome platable
Uses: Lab equipment, electronics, Automotive products-> instrument panels, sheathing cables, carpet
ABS
Properties: high impact and tensile strength, absorbs and redistributes energy on impact, good chemical, weather and UV resistance, very tough, hard, wide colour range, chrome platable
Uses: automotive body parts, household electronics, electrical appliances, business equipment
PLA
Properties:carbon neutral, non toxic, dissolvable with organic solvents, high tensile strength, smooth appearance, castable, low melting point, weldable, transparent
Uses: Automotive interiors, medical implants-> screws, plats, pins, rods, mesh
PVC
Properties: High tensile strength, tough, good impact and abrasion resistance, hardness can be controlled, flexible, poor conductivity, nonflammable, can be transparent or coloured, good chemical resistance
Uses: automobile parts-> instrument panels, sun visor, seat coverings, mud flaps, floor coverings, drain pipes, furniture, Electronic equipment-> insulation, bedding
Nylon
Properties: strong, good abrasion, heat, and electrical resistance, resists petroleum oils and solvents, translucent, wide colour range, flexible, can operate at high temperatures, able to be moulded
Uses: Gears, rollers, guides, bearings, wear pads
