Characterization of metallic powders: a high stakes matter for industrialists

This process is sensitive to changes in particle sizes and shapes in the powder being used. These geometrical characteristics impact the spread and compactivity of the material during the manufacturing process.

To ensure a certain level of quality for printed parts, metallic powders need to meet various requirements to be able to perform as intended. Integrated into the French NF E67-010 standard, specifying the technical requirements for metallic powders designated for use in additive manufacturing, the main parameters are:

• Particle Size Distribution usually measured with a laser granulometer in accordance with the ISO 13320 standard making it possible to determine conventional parameters such as D10, D50 and D90.
• Flowability characterized by the average time it takes a powder to flow through a calibrated Hall or Carney funnel in accordance with the ISO 4490/ASTM B213 and ASTM B964 standards respectively
• Bulk and tapped density are measured to characterize a powder’s capacity organize itself and purge trapped air. These tests are performed with a volumenometer inaw the ASTM B527 and ISO3953 standards. The Hausner ratio is the ratio of tapped density to bulk density.
• True density is measured with a pycnometer in accordance with the ISO 12154 or ASTM B923 standards. This value is used to determine theoretical density and the internal porosity of a powder
• Morphology is studied under a Scanning Electron Microscope (FESEM) and under an Optical Microscope to determine the granulomorphology, the sphericity and the agglomeration state of the powder
• Humidity, determined by gravimetry after a drying the sample in accordance with ASTM E1868
• Chemical composition of metallic powders, determined using spectroscopy techniques such as ICP-AES and ICP-MS or elemental techniques to quantify C, H, O, N, S elements. 

Compliance with the requirements associated with these different characteristics allows metallic powders to achieve a low defect rate (porosity, inclusion, etc.) and a high level of compactness in the part being manufactured, which in turn results excellent mechanical properties