Non-Ferrous Flashcards
(25 cards)
Strength properties of metals (M), ceramics (C) and polymers (P)
M: moderately high
C: high (hard)
P: low
Resistance to loss in strength with rise in temp. for metals (M), ceramics (C) and polymers (P)
M: moderate
C: high
P: poor
Ease of fabrication for metals (M), ceramics (C) and polymers (P)
M: moderate
C: high
P: poor
Conduction (thermal/electrical) for metals (M), ceramics (C) and polymers (P)
M: conductor
C: insulator
P: insulator
Resistance to chemical attack for metals (M), ceramics (C) and polymers (P)
M: poor
C: inert
P: inert
Dimensional stability (stiffness) for metals (M), ceramics (C) and polymers (P)
M: conductor
C: insulator
P: insulator
Lustre for metals (M), ceramics (C) and polymers (P)
M: excellent
C: poor
P: poor
Aluminium:
- Low density material
- Application mostly for automotive sector
- Alloy designation indicates alloy additions
- Microstructure development via grain size and precipitates is opportunity to increase mechanical strength
- FCC structure - ductility maintained even at low temps.
Aluminium - alloy designation:
Four digit number with:
- first digit describing the alloy element
- a dot after the third digit if it is a cast alloy
Cast alloys are brittle to the degree that…
shaping by deformation is not possible and must be fabricated by casting
Aluminium alloys are characterised by
- relatively low density (2.7g/cm^3)
- high electrical/thermal conductivity
- resistance to corrosion in some common environments
Chief limitation of aluminium alloys
low melting temp (600 degrees celsius)
FCC structure of aluminium alloys means
ductility retained at low temps
Mechanical strength of aluminium alloys can be increased by…
cold work and by alloying, however BOTH PROCESSES TEND TO DECREASE RESISTANCE TO CORROSION
Aluminium alloys are classified as either…
cast or wrought
Aluminium alloy compositions are designated by 4 digit number that indicates…
principle impurities and sometimes purity level
Precipitation hardening
- heat treatment technique used to increase yield strength of malleable materials, including most structural alloys of aluminium
- precipitation hardened aluminium alloys have higher tensile strength than conventional as-cast alloys
For cast alloys - decimal located between last two digits, after these digitsis a hyphen and the basic temp designation…
F - fabricated
H - strain hardened
O - annealed
Explain precipitation hardening
- formation of precipitates accomplished by solution treatment at high temps prior to quenching
- heating results in single phase solution while the quenching results in stable material by preventing propagation of lattice defects, greatly strengthening the metal matrix
- a balance must be struck between increasing in strength and resulting loss of ductility and hardness
Ceramics:
- in-organic
- there are different classes of high-performance ceramics
- wear resistant but brittle materials
- widespread use due to excellent corrosion resistance properties
- fabrication from powders via sintering
What are the three classes of modern ceramics?
- oxides: very good corrosion resistance
- carbides: based on on carbon combined with another metals
- nitrides: based on nitrogen combined with some other metals
Glasses:
- amorphous materials (without clear crystal structure)
- brittle but often transparent
- processing is from highly viscous-melt
- used for various optical applications such as lenses, fibres, or coatings
- often very good corrosion resistance
Main differences between glass and ceramics is crystal structure, why is this?
- when quenching atoms don’t have sufficient time to move into perfect crystal lattice
- crystallinity affects optical properties
Differences between glass and ceramics:
- glass does not need to be in-organic, can be metal or polymer
- tensile strength of glass far below metals and technical ceramics
- Young’s Modulus high, above typical metals but slightly below technical ceramics
