Sintering shrinkage of cold compacted iron: effect of thermodynamic driving force, structural and geometrical activity

ABSTRACT

The sintering shrinkage of tapped powders and prior cold compacted specimens of sponge and water atomised iron powders was investigated. The behaviour of the tapped powders is only determined by the driving force and that of the green compacts is strongly affected by modifications caused by cold compaction, which introduce a structural and a geometrical activity that enhance the kinetics of shrinkage. While the tapped powders display only an isothermal shrinkage, the green specimens display an additional large and anisotropic anisothermal shrinkage which is independent on the surface area of the powders. The effect of prior cold compaction tends to run out during the heating step of the sintering cycle.

KEYWORDS:

• Shrinkage
• driving force
• powder morphology
• structural activity

Acknowledgements

Authors are grateful to Professor Riccardo Ceccato, Trento University, for the BET analyses and to eng. Riccardo Crosa and Dr Federico Della Ricca of Höganäs AB for the supply of the powders

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

S. Baselli

S. Baselli received the PhD in Materials, Mechatronics and System Engineering in 2020 from University of Trento and is currently post-Doc at the Department of Industrial Engineering,Trento University. Her reserach activity is focused on the study of sintering of prior cold comapcted metallic powders. She received the Master theis award from EPMA in 2017.

A. Molinari

A. Molinari received the Ph.D. degree in Metallurgical Engineering in 1986 from Torino technical University, Italy. He is currently a full professor of the Department of Industrial Engineering, Trento University. His main research activity is devoted to the study of mechanisms of cold compaction and of sintering of metallic powders, of mechanical properties of sintered steels, and to the application of AM in medical industry. He received Honor Ph.D. by UniversityCarlos III, Madrid in 2016 and by Cracow Technical University in 2019, and is Fellow of EPMA and of APMI.