Lecture 1 Flashcards
what are the main improved properties that reinforcing a composite improves over a metal
fatigue life,
specific strength and specific stiffness
dimensional stability
corrosion resistance
what are the 5 geometrical/spatial characteristics of the dispersed phase that influence the components properties?
concentration, size, shape, distribution, orientation of fibres.
what are metal matrix composites
metal matrix reinforced by a second phase.
what are the two types of reinforcing phases that reinforce an MMC?
ceramic particles (cermets) Fibres of various materials: other metals, ceramics, carbon and boron.
What does reinforcing a ductile metal matrix deliver? Give 5 examples
higher specific strength, spec stiffness, abrasion resistance, creep resistance, lower CTE, better irradiation performance.
what is the specific stiffness also known as?
specific modulus of elasticity
what improvements do MMCs have over PMCs in terms of working temperatures, fire, moisture.
higher operating temps,
non-flammability,
resistance to degradation through organic fluids,
less moisture absorption
Why is the use of MMCs less widespread?
they’re much more expensive to fabricate.
What are the two issues in the matrix/reinforcement interaction at manufacture or operation, and how are they resolved?
- degradation caused by high temps (working or processing), solved by applying protective surface coat to reinforcement, or modifying matrix alloy composition.
- galvanic corrosion, where materials at opposite ends of the galvanic series meet and exposed to corrosive atmosphere, solved by being treated or coated.
What are the characteristics of a metal matrix, and give some examples?
usually a light metal supporting reinforcements, give a certain level of ductility.
examples: aluminium, magnesium, titanium, copper.
what are the main functions of the matrix?
transmits stress to fibres,
protects fibres from surface damage (abrasion or chemical reaction)
Separates fibres & prevents propagation of brittle cracks between fibres.
what are whiskers and how susceptible are they to flaws?
thin crystals with large length to diameter ratios.
flaw free since they are small therefore strongest known materials.
what are the main objectives when reinforcing a metal alloy? (8)
specific yield/tensile at room temp whilst having ductility/toughness. creep resistance at high temps fatigue strength at high temps thermal shock resistance corrosion resistance stiffness (Young's modulus) thermal elongation (CTE)
