Week 12 - Powder Metallurgy 3

Liquid Phase Sintering (LPS)

Through mixing, additives turn into liquid (not base material). This causes them to fuse around the base particles in a 3D holding structure due to rapid transport and sintering. To achieve must:

• Good wetting between solid and liquid

• Good solubility of solid and liquid

• Sufficient amount of liquid

Solid state Sintering - No liquids at all, slower desnification, but better dimensional control, wrose density.

Hybrid desnification and methods

Combining high pressures and temperatures to sinter. Removes large amounts of pores and great properties, such as strength, ductility and uniformness. Types are:

1. Uniaxial hot pressing - Die + heater (takes ages, but simple)

2. Spark plasma sintering - Electricity heats powder directly within (extremely fast and accurate, with great density (very expensive)).

3. Hot isostatic pressing (JIP) - Gas all around die, which presses all together in how temperatures. Uniform pressure and can do complex shapes, however, post machining required to remove mould, high equipment costs.

Post - Processing methods

1. Steam oxidation - fe3O4 grows in pores (protects against corrosion, reduces porocity and improves surface hardnesss)

2. Carburization - Heat component in rich carbon area to from martensite on surface.

3. Shot peening - Shoot balls to give residual stresses which will counteract future stress.

4. Impregnation - Force polymer into pores, often before electroplating.

Cost rule of thumbs

Design is small fraction of cost but large influence on said final cost. PM is advantaged in:

1. Near net shape

2. Minimal material waste

Disadvanted in:

1. Tooling does increasing with complexity.

2. Fine powder costs signficantly more, very expensive to produce.