Metals Flashcards
What two groups can metals be split into?
ferrous
non-ferrous
What do ferrous metals contain?
iron
What is a metal alloy?
a material formed by adding various elements to a basic metal in order to improve the mechanical and chemical properties
what is steel an alloy of? How are steels classified?
iron and carbon (mainly iron)
steels are classified by carbon content
Why is chromium used in stainless steel? what % of chromium is contained in these alloys?
it provides a corrosion resistant property.
12-18%
What are some examples of stainless steel in medical applications?
cardiac pacemaker housing
limb prostheses
orthoses
accupuncture needles
Name a type of non-ferrous alloys
titanium based alloys
what are the advantages of titanium based alloys?
lower density compared to steel
higher strength to weight ratio compared to aluminium
excellent corrosion resistance
What are the disadvantages of titanium based alloys?
high material cost
high fabrication cost
low youngs modulus compared to stainless steels (thicker sections can be used to combat this)
What are polymers?
lightweight, corrosion resistant, electrical insulators with relatively low tensile strengths and melting points formed from single units called monomers
What are the two main types of polymer?
plastics
elastomers
What are the two types of plastic?
thermoplastic
thermosets
What are thermoplastics?
display plastic behaviour at high temperatures - their structure is stable at temperature and can be heated, cooled and reheated without much change.
examples are - Polyethylene (acetabular cups) - PVC - ankle foot orthoses - PMMA - bone cement
What are thermosets?
plastics that can not be reformed as during their formation at high temperature, a by product is released from the material - restricts their recyclability
What are elastomers better known as? What are their mechanical properties?
rubbers - they can be deformed enormous amounts (700%) before permanently changing shape
Describe ceramic materials
they are crystalline in structure with an extreme hardness. they are hard, brittle materials with a high melting point , low conductivity of heat and electricity. ceramics do not creep
Give some examples of ceramic materials
glass
brick
diamond
Why is it desirable to reduce grain size during manufacture of ceramics?
reduces pore size between grains therefore reduce the amount of defects and prevent reductions in tensile strength and toughness.
Name the 3 types of composite materials
particulate-reinforced
fibre-reinforced
laminar reinforced
Describe particulate reinforced composites - give an example
hard brittle material dispersed in a softer more ductile material e.g. concrete (gravel + cement)
Describe fibre reinforced composites - give an example and examples of the benefits
incorporate a strong, stiff, brittle material dispersed in a softer more ductule material to improve strength, fatigue resistance and strength to weight ratio.
e.g. fibreglass / concrete blocks reinforced with steel rods
Describe laminar reinforced composites and give examples.
Can take different forms - LAYERED
a very thin corrosion resistant coating may cover a material to improve corrosion resistance
thicker layers may be laminated together to improve strength e.g. plywood alternating layers of wood veneer at right angles each layer.
