When you look at MIM powder under a scanning electron microscope (SEM), the particle shapes tell a story about how the powder was made — and how it will behave in the MIM process.
Particle shape types found in MIM powder:| Shape | How It Is Produced | Apparent Density | Flowability | Sintering Activity | Typical Oxygen |
|---|---|---|---|---|---|
| Spherical | Gas atomization (inert gas) | High (4.0-5.0 g/cm³) | Excellent (15-20 s/50g) | Moderate | < 0.1% |
| Near-spherical | Water-gas combined atomization | Moderate-High (3.8-4.5 g/cm³) | Good (18-25 s/50g) | High | 0.08-0.15% |
| Irregular / angular | Water atomization | Low (2.5-3.5 g/cm³) | Poor (35-45 s/50g) | Very high (large surface area) | 0.2-0.5% |
| Satellite particles | Attached smaller particles on larger ones (all atomization methods) | Reduces effective density | Reduces flowability | Uneven — satellite sinters differently | Varies |
- Flowability: Spherical powders flow freely through the molding machine hopper and fill the mold evenly. Irregular powders bridge and hang up, causing inconsistent shot weights
- Binder demand: Irregular powders need more binder (lower powder loading) because they pack less efficiently, which increases shrinkage and shrinkage variation
- Sintering: Irregular particles have more surface area and sinter faster — but the sintered density is typically lower because the initial packing density is lower
- Surface finish: Spherical powders produce smoother as-sintered surfaces (Ra 1.6-2.5 µm vs 2.5-4.0 µm for irregular)
Powder morphology refers to the shape and surface features of individual powder particles. Spherical particles (gas atomized) offer the best flowability and packing but higher cost. Irregular particles (water atomized) sinter more actively but require more binder and produce rougher surfaces. Near-spherical particles (water-gas combined atomized) offer the best balance of cost and performance. The morphology is visible under SEM and directly affects feedstock behavior, sintering response, and final part quality.