Altering properties of materials
Presented by Tim Hilditch
Deakin University CRICOS Provider Code: 00113B
Altering or improving material properties
To change the properties of a material, we need to understand how the
structure of the material controls the property we want to change
Altering or improving material properties
To change the properties of a material, we have three main options:
• Change the composition – add one or more different elements
• Change the internal structure – typically by using heat treatments or deformation so
that the arrangement of the atoms within the material is different
• Add reinforcement – the addition of a distinctly different material with properties we
want to produce a composite material
Altering properties
What do you notice about the “bubbles” for the different type of materials in the metals,
ceramics and polymers regions of the strength chart (compared to Young’s modulus)?
Manipulating strength in metals
For metals, we are often trying to manipulate the strength when we alloy or heat treat –
this means trying to make it harder for dislocations to move (i.e. resist plastic deformation)
Pure metal
- In some metals (such as steel and titanium) we
can also change the unit cell (some unit cells are
naturally more resistant to dislocation motion)
Example – carbon in iron (steel)
Very small additions of
carbon into iron provides
drastic increases in strength
- Initially due to individual
atom strengthening (solute)
before starting to form larger
particles or regions
Strengthening metals
Alloying - an alloy is a mixture of a metal with at least one other element
Heat treatment – Temperature allows the atoms to rearrange – controlled cooling allows us
some influence over how they are arranged once back at room temperature
Work hardening – plastic deformation of most metals make them stronger, so using deformation
processes that allow high levels of deformation can produce very high strength materials
Our metals trade-off
The strengthening mechanisms we typically use for a given metal class generally
results in a decrease in ductility (generally means not always)
Polymer Crystallinity
Crystallinity in polymers is important because it:
 Increases Strength and Modulus
How to increase the crystallinity in (most) polymers:
• Draw it! (it aligns the chains)
• Heat treat it! (annealing)
Polymer additives
• Fillers – improve mechanical strength, abrasion resistance and toughness and are
often particulate (wood flour, silica flour, glass, clay, talc, limestone
• Plasticizers – improve flexibility, ductility and toughness and are molecules that help
lower the glass transition temp
• Stabilizers – counteract any deterioration from environmental effects, such as light
• Colourant – dyes or pigments to add colour
• Flame retardant – most polymers are flammable in their pure form
Reinforcements
Polymers and
ceramics are more
difficult to strengthen
than metals – a good
solution is to add a
second material
1.
2.
3.
What you should do now
• Ensure you can explain different ways to improve the strength of a metal,
polymer or composite