Lecture 4 Flashcards
what is the focus of the process selection
giving the desired type quantity and reinforcement of the reinforcement phase, the matrix alloy and specific application
what is powder metallurgy
producing metal productz from powders
What is gas atomisation? what is the finished product? What is the judgement of the process?
molten metal inserted into a gas stream,
gas forced through high energy jets which causes the molten metal to disintegrate and solidify into a PERFECT SPHERE.
Judgement - very efficient
what type of composites would powder metallurgy make?
short fibre or nanosized particulate
How do you make the powders for powder metallurgy
gas atomisation
overall what is powder processing?
blending matrix/reinforcement to produce homogeneous distribution
then cold pressing and sintering (hot pressing) to fabricate particle.
What is the structure achieved from mechanical alloying?
homogeneous composite particles with an intimately dispersed uniform internal structure.
what are the properties achieved from mechanical alloying and at what temperature?
dispersion strenghtened, age hardened in a HIGH temp alloy.
what are the characteristic of dispersion particles and what effect does it have.
very fine particles,
dramatic strengthening effect
what is the process of mechanical alloying?
- compressed in a ball mill
- hot pressed and sintered
- heat treated to remove the residual stresses
why is mechanical alloying seen as a good thing for some metals?
some elements are not soluble in metal, and so crushing them into a powder allows mixture.
what is roll bonding?
where two materials are compressed together through rolling
describe diffusion bonding?
diffusion of atoms between metallic surfaces in contact at high temperature leads to bonding
what is common about the conditions applied to induce diffusion bonding?
high temp and pressure APPLIED
briefly describe the diffusion bonding process
the fibre and matrix are stacked up in a layered way (fibre - foil - fibre) , then there is a controlled atmosphere of temp; and pressure is applied (sintering).
