Introduction to materials Flashcards
LEARN everything!
What is materials science?
The use of materials and our ability to exploit our environment
Human history is divided by technological sophistication in creating tools. Name the different ages…
Paleolithic
Mesolithic
Neolithic
Chalcolithic
Bronze age
Iron age
What are intrinsic material properties dictated by?
Atomic structure and crystal formation
What does the atomic scale dictate?
reactivity of the material, density, reflectivity, thermal and electrical conductivity
What does the crystal scale dictate?
Mechanical properties:
ductility, what loads it can withstand without yielding
What can control the overall properties of a product made from the material being processed?
The size and directionality of the crystals, presence of any unexpected features, e.g. inclusions
What influence does the scale of a material have
The finer the scale the, least influence we can have
atomic bonding is fixed
crystal structure can be influenced by processing, can dictate the conditions that prevent the formation of crystals leading to noncrystalline or amorphous materials
we can do more to influence the growth of crystals and the phases the form, having greater effect on the properties of a material.
What are the classifications of materials?
- Metals, ductile with high electrical and thermal conductivities
- Polymers, soft and viscous and low mp
- Ceramics, brittle and high mp
- Composites, comprised of particles or fibres of one type of a retrial embedded in another
Properties of Metals
- High mp (up to 1536 oC for Fe)
- Can be casted
- Ductile, due to metallic bonding and atomic packing, can be readily deformed = rolling, deformation is easier if material is hotter –> reduces yield stress = easier plastic deformation requiring less force
- Forging
- Extrusion
- Machining
- Welding
Forging?
Metal is deformed to a new shape by the application of force
Extrusion?
Metal is forced through a die to form a new cross-section , and drawing, to make cup-shaped objects
Machining?
(plastic deformation process), machine tool deforms the workpiece resulting in pieces of metal being sheared away which break off
Welding?
Low mp, so can locally melt and allows molten parts to mix together so when they solidify they are a single component
What are the properties of Polymers?
- low mp compared to metals (few 100 oC)
- combustible
- v. viscous in liquid state
- can be plastically deformed
- Commonly extruded, made into shapes and sheets and be welded to metals
- v. viscous therefore can’t be cast, but can be squeezed –> injected into die or rolled into sheet
- low thermal conductivity
Viscous?
liquid polymers can support their own shape while in the liquid phase, leading to shaping processes that could not be applied to metals, e.g. blowing to make polymer bottles
Low thermal Conductivity?
not easily uniformly melted, rapping heating can lead to localised combustion instead –> other heating methods with good mixing required
What are the properties of ceramics?
- High mp, cannot be cast
- Brittle (not ductile), cannot be plastically deformed
- Shaped using powder processing
- worked in a slurry
Powder processing of ceramics?
ceramics are reduced to powders which are moulded into the required shape and then heated. At a high enough T, powders bond (sinter) to form a dense product
Working ceramics in a slurry
slurry is poured into a mould and then carrier liquid is drawn off to leave a viscous layer at the surface, to be removed then sintered or fired. ceramics can be treated like liquids despite different properties
What are composites?
Mixtures of different materials
What is the reinforcement used for composites?
Can be either particulate or whisker form, and be introduced into a matrix of metals, polymers and ceramics
What is the result of a composite?
New material, with mixture of properties from reinforcement and matrix material
Name 2 examples of composites
- GRF ( glass- reinforced plastic), matrix of resin into which glass fibres are mixed
- MMCs (metal-matrix composites) a mixture of ceramic particles in a metal matrix
Name the 3 material structures that influence properties
Atomic bond
Atomic packing arrangement
Micro or macro structure
What structures combine to give the overall properties of metals?
mp, ductility - metallic bond that keeps the atoms together
ductility - atomic packing
What structures combine to give the overall properties of Polymers?
low mp - covalent bonding
deformability - molecular architecture, long chain molecules
What structures combine to give the overall properties of Ceramics ?
high mp, lack of ductility- ionic nature of bonding
Do the processing methods have a bearing on the properties obtained?
Yes
How can the macro and microstructure of materials be changed?
Processing operation
Process operations involving metals
shaping - heating = phase changes that alter the microstructure , hence strength
Process operations involving polymers
changes the amount of crystallinity (microstructure) , alters the polymer strength
Process operations involving ceramics
sintering - has variable effect on the removal of pores that naturally occur between powder particles packed together. Amount of piers alters mechanical properties
What is archaeomaterials?
science of the study of how materials were exploited in the past
extends to study of material original’s, extraction form ore, trading, processing, structure, and subsequent properties
