Alloy element redistribution during sintering of powder metallurgy steels
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Homogenization of alloying elements is desired during sintering of powder metallurgy components. The redistribution processes such as penetration of liquid phase into the interparticle/grain boundaries of solid particles and subsequent solid-state diffusion of alloy element(s) in the base powder, are important for the effective homogenization of alloy element(s) during liquid phase sintering of the mixed powders. The aim of this study is to increase the understanding of alloy element redistribution processes and their effect on the dimensional properties of the compact by means of numerical and experimental techniques.
The phase field model coupled with Navier-Stokes equations is used for the simulations of dynamic wetting of millimeter- and micrometer-sized metal drops and liquid phase penetration into interparticle boundaries. The simulations of solid particle rearrangement under the action of capillary forces exerted by the liquid phase are carried out by using the equilibrium equation for a linear elastic material. Thermodynamic and kinetic calculations are performed to predict the phase diagram and the diffusion distances respectively. The test materials used for the experimental studies are three different powder mixes; Fe-2%Cu, Fe-2%Cu-0.5%C, and Fe-2%(Cu-2%Ni-1.5%Si)-0.5%C. Light optical microscopy, energy dispersive X-ray spectroscopy and dilatometry are used to study the microstructure, kinetics of the liquid phase penetration, solid-state diffusion of the Cu, and the dimensional changes during sintering.
The wetting simulations are verified by matching the spreading experiments of millimeter-sized metal drops and it is observed that wetting kinetics is much faster for a micrometer-sized drop compared to the millimeter-sized drop. The simulations predicted the liquid phase penetration kinetics and the motion of solid particles during the primary rearrangement stage of liquid phase sintering in agreement with the analytical model. Microscopy revealed that the C addition delayed the penetration of the Cu rich liquid phase into interparticle/grain boundaries of Fe particles, especially into the grain boundaries of large Fe particles, and consequently the Cu diffusion in Fe is also delayed. We propose that the relatively lower magnitude of the sudden volumetric expansion in the master alloy system could be due to the continuous melting of liquid forming master alloy particles.
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xvi, 45 p.
TRITA-MEK, ISSN 0348-467X ; 2014:13
Cu redistribution kinetics, diffusion, phase field modeling, powder metallurgy, swelling, liquid phase sintering
Engineering and Technology Metallurgy and Metallic Materials
Research subject Materials Science and Engineering; Engineering Mechanics
IdentifiersURN: urn:nbn:se:kth:diva-145251ISBN: 978-91-7595-137-9OAI: oai:DiVA.org:kth-145251DiVA: diva2:717356
2014-05-26, F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
Torralba, Jose Manuel, Professor
Amberg, Gustav, Professor
QC 201405152014-05-152014-05-142014-05-15Bibliographically approved
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