Week 10 - Powder Mettalurgy

Powder Metallurgy process and reasons for use

Powder → Blend → Shape → Sinter → Post Process

1. Low cost, high precision coponent

2. Unique properties such as controlled porosity.

3. High Tm or reactive metals can be done.

Particle shape and inter particle friction

Shape → Controls friction → Controls density → Controls powder flow → Controls compaction pressure

AR can be used to measure, 1 is a sphere 1.05-1.4 is used for PM

Higher friction → Increased angle of response → Lower packing density

Ways to make particles

• Atomisation, three different kinds

1. Gas - Gas blobs split up liquid metal (good for reactive metals)

2. Water - splids up metal (iron, steel, low reactivity)

3. Centrifugal - Spits out in circle (Good for extremely reactive)

• Chemical fabrication - Put through galvanic cell, resulting powder builds up is used. Gives great purity, can’t use for alloys and poor packing shape

• Attrition and metal alloying - All in a big tub full of powder, splits into balls. Can prepare composites of constant size but powder is angular shaped and highly worked.

• Jet milling - Two powders shot at each other, low contamination, but high energy and expensive.

Lubricants vs Binders

Lubricants - Reduce friction during compaction

Binders - Hold green body together after shaping, increasing strength. Eventually melted out.

Agglomeration - Causes and solutions

When particles, like to bond together, by liquid, intermolecular forces or even just inerlocking. Need to remove through removing moisture, adding polar dispersants, applying shear to the powder.

Particle size distribution - D10/D50/D90

DXX - XX of all particles are SMALLER then this value.