It is well established that particle size and shape substantially influence the bulk properties of powdered materials. Although these characteristics are closely interrelated, the tendency has been to analyse the particle size independently from particle shape. The aim of this work was the assessment of particle shape through particle sizing data. For this purpose, three different particle shape materials – glass beads (spherical), crushed glass (moderately irregular) and mica (lamellar) – were tested, employing four particle sizers. The shape factor selected was the Wadell's sphericity, which was evaluated utilizing distinct equations. The comparison of the results reveals problems arising from the use of approximations rather than more fundamental equations.
a b s t r a c tThe current trend towards miniaturization has led to the increasing use of stainless steel powders as raw material in the manufacture small parts with complex shapes, e.g. medical devices. This paper focuses on the role of coated and uncoated low carbon stainless steel powders, having d 50 = 7.3 m, normal particle size distribution and a shape factor of 1 on additive processes used in micromanufacturing, e.g. micro powder injection moulding (PIM). Surfaces were treated using a magnetron sputtering deposition apparatus equipped with a high frequency powder vibration and a continuous feed system. The results clearly show that the coated powders assume an "artichoke" morphology, which significantly increases the surface area. This combined with their nanocrystalline character leads to higher flowability than uncoated powders. However, no improvements have been observed concerning the critical powder volume concentration (CPVC) in feedstocks for PIM processing. In consolidation processes, the debinding temperatures can attain values higher than 500 • C. After debinding and sintering, the coating of steel powders can show lower carbon contamination in solid solution than uncoated ones. This result is very important particularly for powder microtechnology of low carbon stainless steel.
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