Meaning
Physical shape and surface structure of individual powder grains generated through atomization, chemical precipitation, or mechanical milling. Particle morphology influences both the flow behavior of bulk powder and the consolidation behavior of the material during manufacturing. This geometrical property ranges from highly spherical to irregular, dendritic, or flaked shapes.
Process Relation
Spheroidization of droplets occurs when the surface tension of the liquid metal overcomes the cooling rate during atomization. When the cooling rate is exceptionally high, the droplets solidify before they can minimize their surface area, resulting in non-spherical shapes. Gas atomization with inert gases typically produces spherical powder because it allows longer solidification times.
In contrast, water atomization produces highly irregular particles due to rapid thermal quenching.
Performance Effect
Powders with high sphericity flow more easily and pack with greater density than those with irregular geometries. This high packing density is critical for powder bed processes, where it ensures a uniform layer thickness and a high final part density. On the other hand, irregular particles are preferred in conventional press-and-sinter applications because their shapes allow mechanical interlocking.
This interlocking increases the green strength of the compacted part before it enters the sintering furnace.
Characterization Technique
Optical and electron microscopes are used to analyze the contour and surface texture of the consolidated grains. Image analysis software processes these microscopic views to calculate the aspect ratio and circularity of the particles. Automated measurements provide statistical distributions of these shape factors across the batch.
These metrics are used to qualify the powder for industrial applications.
