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Alloy element redistribution during sintering of powder metallurgy steels
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.
Series
TRITA-MEK, ISSN 0348-467X ; 2014:13
Keyword [en]
Cu redistribution kinetics, diffusion, phase field modeling, powder metallurgy, swelling, liquid phase sintering
National Category
Engineering and Technology Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering; Engineering Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-145251ISBN: 978-91-7595-137-9 (print)OAI: oai:DiVA.org:kth-145251DiVA: diva2:717356
Public defence
2014-05-26, F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140515

Available from: 2014-05-15 Created: 2014-05-14 Last updated: 2014-05-15Bibliographically approved
List of papers
1. Initial rapid wetting in metallic systems
Open this publication in new window or tab >>Initial rapid wetting in metallic systems
2013 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 61, no 14, 5375-5386 p.Article in journal (Refereed) Published
Abstract [en]

The initial rapid wetting of a solid surface by a liquid phase is an important step in many industrial processes. Liquid-phase sintering of powder metallurgical steels is one such industrial process, where metallic powders of micrometer size are used. Investigating the dynamic wetting of a high-temperature metallic drop of micrometer size experimentally is very challenging. Here, a phase-field-based numerical model is first implemented and verified by accurately capturing the initial dynamic wetting of millimeter-sized metal drops and then the model is extended to predict the dynamic wetting of a micrometer-sized metal drop. We found, in accordance with recent observations, that contact line friction is required for accurate simulation of dynamic wetting. Our results predict the wetting time for a micrometer-sized metal drop and also indicate that the dynamic wetting patterns at the micro- and millimeter length scales are qualitatively similar. We also found that the wetting process is much faster for a micrometer-sized metal drop compared to a millimeter-sized metal drop.

Keyword
Dynamic wetting, Phase field, Contact line friction, Millimeter- and micrometer-sized Cu drop, Powder metallurgical steels
National Category
Metallurgy and Metallic Materials Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-127476 (URN)10.1016/j.actamat.2013.05.026 (DOI)000322750800022 ()2-s2.0-84882452190 (Scopus ID)
Funder
Vinnova
Note

QC 20130905

Available from: 2013-09-05 Created: 2013-08-30 Last updated: 2017-12-06Bibliographically approved
2. Investigation of Cu distribution and porosity in Fe-2Cu and Fe-2Cu-0.5C compacts
Open this publication in new window or tab >>Investigation of Cu distribution and porosity in Fe-2Cu and Fe-2Cu-0.5C compacts
Show others...
2013 (English)In: International Powder Metallurgy Congress and Exhibition, Euro PM 2013, 2013Conference paper, Published paper (Refereed)
Abstract [en]

The distribution of the alloying element Cu in steel compacts is important in determining the properties of the sintered products. In this work, mixtures of Fe-2Cu and Fe-2Cu-0.5C were compacted at 600 MPa and sintered at 1120oC for the holding times of ts= 3, 13, 23, and 33 min. Dilatometry and light optical microscopy is used to investigate porosity, Cu distribution and its effect on the dimensional changes during sintering. The result shows that the molten Cu penetrates into the Fe interparticle and grain boundaries in less then 3 min holding time at 1120°C, however C addition hinders the liquid penetration of Cu. Furthermore, it is found that the C-added compact has lower volume expansion and porosity compared to the C-free system, after 33 min of holding time at 1120°C.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-145298 (URN)2-s2.0-84924975932 (Scopus ID)978-189907240-8 (ISBN)
Conference
International Powder Metallurgy Congress and Exhibition, Euro PM 2013; Gothenburg; Sweden
Note

QC 20140515

Available from: 2014-05-15 Created: 2014-05-15 Last updated: 2015-06-12Bibliographically approved
3. Cu redistribution during sintering of Fe–2Cu and Fe–2Cu–0·5C compacts
Open this publication in new window or tab >>Cu redistribution during sintering of Fe–2Cu and Fe–2Cu–0·5C compacts
Show others...
2014 (English)In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 57, no 5, 373-379 p.Article in journal (Refereed) Published
Abstract [en]

The effective use of alloying elements in powder metallurgical steels requires a deep understanding of their redistribution kinetics during sintering. In this work, interrupted sintering trials of Fe–2Cu and Fe–2Cu–0·5C compacts were performed. Moreover, diffusion simulations of Cu in γ-Fe using Dictra were performed. It is found that transient liquid phase penetrates the Fe interparticle and grain boundaries in less than 3 min of holding time. However, C addition limits the penetration of liquid Cu, particularly into grain boundaries of large Fe particles. The results also show that the mean diffusion distance of Cu in γ-Fe in the C added system is slightly lower than that in the C-free system at 3 min of holding time; however, after 33 min, the mean diffusion distance is similar in both systems. The diffusion distances of Cu in γ-Fe, predicted by Dictra, are in good agreement with the measured values.

Keyword
Cu redistribution kinetics, Diffusion, Wetting, Microstructure, Dilatometry, SEM/EDXS, Dictra, Powder metallurgical steels
National Category
Metallurgy and Metallic Materials Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-145295 (URN)10.1179/1743290114Y.0000000085 (DOI)000347974900011 ()2-s2.0-84919432962 (Scopus ID)
Note

QC 20150220

Available from: 2014-05-15 Created: 2014-05-15 Last updated: 2017-12-05Bibliographically approved
4. Behavior of master alloy during sintering of PM steels: redistributionand dimensional variations
Open this publication in new window or tab >>Behavior of master alloy during sintering of PM steels: redistributionand dimensional variations
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-145296 (URN)
Note

QS 2014

Available from: 2014-05-15 Created: 2014-05-15 Last updated: 2014-05-15Bibliographically approved
5. Modeling of the primary rearrangement stage of liquid phase sintering
Open this publication in new window or tab >>Modeling of the primary rearrangement stage of liquid phase sintering
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-145297 (URN)
Note

QS 2014

Available from: 2014-05-15 Created: 2014-05-15 Last updated: 2014-05-15Bibliographically approved

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