Evaluation of different particle size distribution and morphology characterization techniques

In this paper, the particle size distribution (PSD) and morphology for six different metal powders were measured and compared using a range of techniques which included laser diffraction, static imaging, and dynamic imaging. The metal powders were chosen from a diverse end-use (Metal Injection Moulding, Laser - Powder Bed Fusion, Electron Beam - Powder Bed Fusion, and Hot Isostatic Pressing) and varied in powder size distribution and morphology. While the results for particles that were predominantly spherical showed some general agreement for the measured PSD across the range of measurement techniques investigated, larger variation than industrial tolerances would allow was identified when comparing the results between the different measurement techniques. The technique did influence the measured PSD at times, with differences large enough to require compensation if used for critical applications with tight tolerances. For samples that had particle morphologies that deviated away from spherical (agglomerated, irregular, or satellited), the difference in the measured PSD was more significant when comparing the results from the different measurement techniques. This was due to the under/overestimation of the PSD due to the measurement principles of the system being employed. Thus, when reporting PSD, it is of paramount importance to align specification requirements, and the certification test methods, with the industrial controls (i.e., laser diffraction when used in production to tune air classification). If different instruments or techniques are to be used by a purchaser and supplier, any inherent bias must be understood. For morphology, static imaging tends to result in a higher measured value for sphericity and aspect ratio in comparison to dynamic imaging. This is believed to be due to the influence of orientation during measurement as well as the resolution of the optics.