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Powder metallurgy process and applications

Short answer

Powder metallurgy: powder production (atomisation), blending, compaction in a die at high pressure to form a green compact, sintering below melting point to bond particles, and optional secondary operations. Advantages: near-net shape, minimal waste, controlled porosity. Limitations: costly tooling, size limits, lower strength. Products: self-lubricating bearings, gears, carbide tips, filters.

Describe the powder metallurgy process with its main steps. Mention its advantages, limitations and four typical products.

Powder metallurgy (PM) makes parts by compacting metal powders in a die and then heating (sintering) them below the melting point so that the particles bond.

Steps

  1. Powder production - atomisation (molten metal broken by water or gas jet), chemical reduction of oxides, electrolytic deposition. Particle size is about 10-200 micrometre.
  2. Blending and mixing - different powders, alloying elements and a lubricant (about 1 percent zinc stearate) are mixed.
  3. Compaction - powder is pressed in a hardened die at 150-700 MPa to give a "green compact", with density about 70-90 percent of solid metal and enough strength to be handled.
  4. Sintering - the compact is heated in a protective atmosphere at about 70-90 percent of the melting temperature (about 1100-1150 degree C for iron) for 15-60 min. Diffusion welds the particles and strength rises.
  5. Secondary operations - sizing or coining, impregnation with oil, infiltration, heat treatment and machining.
Powder -> Blend -> Press (die) -> Sinter -> Size/finish
                      |
                  green compact

Advantages

  • Near-net shape, little scrap (over 95 percent material use).
  • Can make parts from materials difficult to cast or machine (tungsten carbide, refractory metals).
  • Controlled porosity (self-lubricating bearings, filters).
  • Good dimensional accuracy and surface finish; economical for large batches.

Limitations

  • High cost of powder and tooling; economical only for large quantities.
  • Size limited by press capacity; complex shapes with undercuts are difficult.
  • Lower strength than wrought metal because of residual porosity.

Typical products

Self-lubricating bronze bearings, gears and cams, cemented carbide tool tips, filters, electrical contacts and sintered magnets.

✓ Answer checked by Claude Opus 5.5 (high effort)

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