Powder Metallurgy Flashcards
Beginning in powder form, material is pressed/compacted into a desired shape to form a green compact
what is a green compact?
Where the metal in unprocessed and can be broken very easily
green compacts are sintered/heated to bond the particles to be come more hard.
how hot is the sintering procedure
below the melting point but above the recrystallisation temperature
advantages of powder metallurgy
- component can be near net shape
- little waste
- can be automated for economical production
disadvantages of powder metallurgy
- high equipment cost
- powders are expensive
- problems with storing metal powder (degradation over time/ fire hazards)
- limitations on part geometry which lead to varied dense spots
what are the two categories of metal powders
- elemental powders
- pre alloyed powders
what is elemental powder used for
can be mixed to create alloys e.g. cermet’s/tool steels
problems with using water for atomisation
can lead to corrosion/oxidation and is solved in modern day by using synthetic oils instead of water
what are the three ways to produce metallic powders
- Atomisation
- Chemical
- Electrolytic
what are the three next steps after acquiring the powder
- Blending and mixing (binders and lubricants may be added during blending)
- Compaction
- Sintering (gets heated up to strengthen bond)
why is sintering better with a bigger surface area of powders
the finished component will be more dense. This is because atoms in the centre have bonding forces in all directions where as atoms near the surface are not.
why might there be secondary operations on sintered parts
to increase density, improve accuracy or additional shaping
what is porosity
A technique where the pore spaces are filled with oils or polymers.
Two key methods are impregnation and infiltration
what is heat treatment on powder metallurgy parts for
To increase strength of component, make it corrosive resistant and improve appearance
what are the alternative pressing and sintering techniques
-Isostatic pressing (where pressure is applied from all direction to make it more compact)
-powder injection Moulding
-Powder Rolling
-Hot pressing (Combining pressing and sintering into ne step)
Liquid phase sintering
