Prior to sintering the powder must be roughly shaped and binded together. A mixture of powder and polymeric binding agent such as PVA are fed into a rubber mould.

Pressure is applied by a hydraulic system, which slightly compresses the mixture into a solid green compact ready for sintering, this is still very porous.

The green compact is heated to drive off the binder. The temperature is kept well below the melting temperature of the powder.

The powder particles are primarily shaped by diffusion rather than melting. Diffusion takes place through the lattice or grain boundaries so as to move material from the initial contact regions to the growing necks, thus allowing the particle centres to approach each other.

The particle's total volume is conserved, so internal diffusion causes the particle centres to move together. Increasing the density and decreasing the volume of the compact.

The green compact is heated to drive off the binder. The temperature is kept well below the melting temperature of the powder.

Here atoms in the particles diffuse along the surface towards the contact points. (In both cases diffusion is driven by a reduction in surface area).

The particle's total volume is still conserved, but surface diffusion leads to longer necks between particles so the particles do not significantly move. This is a non-densifying process.

Liquid Phase Sintering involves heating a mixture of powders to melt one of them. The melted powder usually makes up a small volume fraction, ~10%.

The liquid flows and wets the other powder. Some consolidation occurs due to the decrease in porosity.

The liquid cools to the solid phase. LPS is faster and results in much lower porosity than conventional sintering, but parts can be susceptible to high operating temperatures.

Reactive processing relies on chemical reaction rather than diffusion to form a solid component from powder. It can be a faster, cheaper alternative to sintering.

In this example the majority component is Silicon Carbide (SiC) with smaller carbon (C) particles interspersed. Liquid silicon (Si) is drawn by capiliary action into this porous structrure.

The incoming Si liquid reacts with the carbon particles to form SiC layers on them, and also on existing SiC particles.

The Si continues to react, and the SiC layer grows. Once the reaction has completed there are still regions of unreacted Si and C left in the structure, as well as within the new SiC.

HIP is a variant of conventional cold pressing and sintering, in which heat and pressure are applied simultaneously. The equipment is expensive and the powder mixture must be sealed in a canning material, such as steel, that can withstand the temperatures involved, and deform plastically.

The can is surrounded by an inert gas (usually argon) at high temperature and pressure.

This pressure is transmitted to the powder mixture, so that individual particles may undergo plastic deformation or creep, accelerating the consolidation process compared with conventional sintering. After cooling, the can is usually machined off the sample.