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In this video, Professor Deliang Zhang and Dr Brian Gabbitas, from the University of Waikato, explain how powder forging can be used to make components. One of the problems encountered is to eliminate small cavities to gain full density of the material. Results have been encouraging, but further work needs to be done.
PROF DELIANG ZHANG
With powder metallurgy, normally we simply press the particles together into a compact and heat it up to sufficiently high temperature but without melting the solid, and then the atoms are so active that they want to diffuse across the boundaries between the particles. Once they do that, the particles will establish atomic bonding. So with powder metallurgy, if say we want to produce a part like this, what we first do is to first press the powder into a shape like this. When you press the powders into a shape like this, the density is about 70–80% of the true density of the material. So after sintering, the majority of the cavity will be closed because the material will move, and the fusion established, but there is normally still like 2% or 3%, up to 5% of cavity still left inside, and that actually is what the industry don’t normally like.
For applications where the strength of the material will have to be really high and also for the material not to fracture, one has to keep moving. So here in the research at the University of Waikato we do other processes to produce thin shapes like this but without any cavities.
DR BRIAN GABBITAS
And we found that we can get almost full density by powder forging, and we are very pleased that that has happened because it looks promising for eliminating additional stages in processing. But having said that, we are still not getting the level of mechanical properties that we need, particularly ductility, and so we are working very hard to try and improve that at the moment.