Sintering
Sintering bonds powder particles below the melting point via atomic diffusion; three routes dominate. Solid-state (conventional PM) sinters steel compacts near 1120°C — about 70-90% of the alloy's melting point — reaching only 80-95% of theoretical density; closing residual pores needs hot isostatic pressing (100-200 MPa) to exceed 99%. Liquid-phase sintering adds a lower-melting second phase (cobalt binder in WC-Co carbide) that flows on heating, hitting ~96.5% density at lower peak temperature — standard for cutting-tool inserts and electrical contacts. Laser powder-bed DMLS sinters Ti6Al4V, 17-4/316L stainless, Inconel 625/718 and AlSi10Mg at 70-90% of melting point, delivering 98%+ density per Xometry's spec, versus full-melt SLM's 99.9%. Density testing follows ASTM B962; composition specs follow MPIF Standard 35. Maintained by No single vendor; process is standardized via ASTM International (B962 density test method, B883 for MIM materials) and MPIF Standard 35 (composition/property specs).
Pick solid-state sintering for cheap, high-volume structural parts (gears, bushings) off conventional PM presses — it wins on tooling cost and throughput, not density. Skip it for anything fatigue-loaded: 80-95% density leaves interconnected porosity that seeds cracks. Need complexity plus near-full density? DMLS beats PM outright at 98%+, but costs 10-50x more per part and can't match PM volume. Liquid-phase sintering is the honest middle ground for cemented-carbide tooling and electrical contacts — MPIF's own literature flags its weakness: the liquid phase that speeds densification also drives shrinkage distortion and grain coarsening that solid-state sintering avoids. Known weakness: Densification in solid-state sintering stalls in the final stage as pores become isolated inside growing grains, capping practical density around 95-97% unless followed by a separate HIP step.