When you receive a MIM powder certificate of analysis, three numbers stand out: D10, D50, and D90. These describe the particle size distribution (PSD) — the single most influential powder parameter after chemical composition. Understanding what they mean and how they affect your parts is essential for specifying powder correctly.
What D10, D50, and D90 actually mean:- D50 (median): 50% of particles (by volume) are smaller than this value. For MIM, the standard is D50 < 20 µm. A coarser D50 reduces sintering activity; a finer D50 increases feedstock viscosity
- D10: 10% of particles are smaller than this value. Very fine particles (<5 µm) increase binder demand and oxygen pickup. If D10 is too low, feedstock becomes difficult to mold
- D90: 90% of particles are smaller than this value. Particles above 30-35 µm sinter poorly and leave residual porosity. A high D90 means visible surface pitting after sintering
| PSD Shift | Effect on Feedstock | Effect on Sintering | Effect on Final Part |
|---|---|---|---|
| Finer D50 (<12 µm) | Higher viscosity, more binder needed | Higher densification rate, more shrinkage | Better surface finish, higher density, but more carbon risk |
| Coarser D50 (>22 µm) | Lower viscosity, less binder | Slower densification, lower final density | Rougher surface, higher porosity, lower strength |
| Broad distribution (high span) | Higher packing density possible | More uniform shrinkage | Better dimensional consistency, lower cost |
The standard MIM specification is D50 10-20 µm, D90 < 35 µm. Bimodal distributions (a blend of fine and coarse fractions) can achieve higher packing density for demanding applications.
Why it matters in production: A PSD shift of just 2-3 µm in D50 can change the sintered density by 1-2 percentage points and alter the shrinkage factor enough to push critical dimensions out of tolerance. This is why reputable MIM manufacturers test every incoming powder lot with laser diffraction — and why ATMIK, with in-house atomization, controls PSD at the source rather than relying on external supplier CoAs.When specifying MIM powder, always request the full PSD report (D10, D50, D90, and span) rather than just the D50. The distribution width is as important as the median.
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