Particle morphology of water atomised iron‑carbon powders

• Published in: Powder technology Vol. 397; p. 116993
• Main Authors: Persson, Fredrik, Hulme, Christopher Neil, Jönsson, Pär G.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.01.2022; Elsevier BV
• Subjects: Atomizing; Carbon; Circularity; Collisions; Hydrogen evolution; Iron; Materials Science and Engineering; Metal powders; Particle shape; Porosity; Teknisk materialvetenskap; Turbulent collisions; Water atomisation; Water breakdown; Porosity; Turbulent collisions; Water breakdown; Water atomisation; Hydrogen evolution; water breakdown; hydrogen evolution; turbulent collisions; porosity
• ISSN: 0032-5910; 1873-328X; 1873-328X
• DOI: 10.1016/j.powtec.2021.11.037

Water atomisation can produce metal powders faster and at lower cost than gas atomisation, but it is well known that the powder particles are irregular and may contain a large number of pores. The current study analyses three iron‑carbon alloys with different superheats, produced as powder by water atomisation and compares the particle shapes and porosity in each. The alloy with the most carbon (4.2 wt%) showed the highest circularity (0.72) for 20–45 μm particles, but the lowest (0.59) for 180-212 μm particles. This is consistent with collisions between droplets affecting particle shape. The lowest-carbon melt (0.22 wt%) solidified fastest, so underwent fewest collisions and showed similar circularity for all particle sizes. The breakdown of water to form hydrogen and the formation of hydrogen bubbles was the most likely cause of porosity. The findings of this study may be used to inform future water atomisation process design to control particle shape and minimise porosity. [Display omitted] •Freezing−/spheroidisation times, droplet collisions give irregular particles.•No significant solid oxide shell was observed on the particle surfaces.•Thermal contraction or gas entrainment alone are unlikely to lead to porosity.•Carbon monoxide/dioxide are too slow-moving to form bubbles in the process.•Water breakdown, leading to hydrogen gas in the drops is a likely cause of pores.