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Variation of nitrogen solubility and mechanism of pore formation during production of porous Fe-Cr-Mn-Si-C material
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2007 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 20, no 2, 73-83 p.Article in journal (Refereed) Published
Abstract [en]

Experiments regarding the synthesis of porous metallic materials were performed by dissolution of nitrogen into molten hypereutectic 77Fe-8Cr-6Mn-5Si-4C (wt-%) and hypoeutectic 79Fe-8Cr-6Mn-5Si-2C alloys, and water quenching. A uniform pore distribution was obtained only for the hypereutectic alloy. To study the effect of the alloy composition and microstructure on the pore distribution, the variation of nitrogen solubility during primary solidification was calculated for both alloys, taking into account the phase composition changes. A mechanism of pore formation is proposed. In the hypereutectic alloy, an increasing nitrogen supersaturation in the melt during primary carbide growth is believed to fuel the growth of nucleated N-2 pores. The primary M7C3 carbides play an essential role in preventing pore coalescence. In the hypoeutectic alloy, a decreasing nitrogen solubility gap between the austenite dendrites and the liquid does not allow extensive pore growth. The absence of primary carbides favours the formation of a single large pore.

Place, publisher, year, edition, pages
2007. Vol. 20, no 2, 73-83 p.
Keyword [en]
porous metals; nitrogen solubility; pore formation; supersaturation; M7C3 carbides ; UNIDIRECTIONAL SOLIDIFICATION; IRON; FABRICATION; ATMOSPHERE; ALLOYS; STEEL
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-7306DOI: 10.1179/136404607X212068ISI: 000250924600008Scopus ID: 2-s2.0-36048985431OAI: oai:DiVA.org:kth-7306DiVA: diva2:12275
Note
QC 20100809. Uppdaterad från Accepted till Published 20100809.Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2017-12-14Bibliographically approved
In thesis
1. On the effect of nitrogen, hydrogen and cooling rate on the solidification and pore formation in Fe-base and Al-base alloys
Open this publication in new window or tab >>On the effect of nitrogen, hydrogen and cooling rate on the solidification and pore formation in Fe-base and Al-base alloys
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Experiments on the production of porous metallic materials were performed on Fe-base and Al-base alloys. The method involves dissolution of gases in the liquid state and solidification at various cooling rates. The alloy compositions were selected to induce solidification of primary particles intended to control the pore distribution. For the Fe-base alloys, nitrogen was introduced into the melt by dissolution of chromium nitride powder. Fe-Cr-Mn-Si-C alloys featuring M7C3 carbide particles were selected. For the Al-base alloys, hydrogen gas was dissolved into the melt by decomposition of water vapor. Al-Ti and Al-Fe alloys featuring primary Al3Ti and Al3Fe intermetallic particles, respectively, were considered. In the Fe-base alloys, a homogeneous distribution of gas pores through the specimens’ volume was obtained at high cooling rate (water quenching) and after introduction of external nucleating agents. In the case of the Al-base alloys, a good pore distribution was observed at all cooling rates and without addition of nucleating agents. Calculations of the variation of nitrogen (respectively hydrogen) solubility based on Wagner interaction parameters suggest that pore nucleation and growth occur during precipitation of the primary particles (M7C3 carbides, Al3Ti or Al3Fe intermetallics), due to composition changes in the melt and resultant supersaturation with gas atoms. Microscopic analyses revealed that the primary particles control the pore growth in the melt and act as barriers between adjacent pores, thereby preventing pore coalescence and promoting a fine pore distribution. Uniaxial compression testing of the porous Al-Ti and Al-Fe materials showed the typical compressive behavior of cellular metals. Further work is needed to improve the quality and reproducibility of the porous structures which can possibly be used in energy absorption or load-bearing applications.

As a corollary result of the quenching of hypereutectic Fe-Cr-Mn-Si-C alloys in the experiments of synthesis of porous metals, a homogeneous featureless structure was observed in some parts of the samples, instead of the equilibrium structure of M7C3 and eutectic phases. Subsequent investigations on rapid solidification of Fe-base alloys at various alloy compositions and cooling rates led to the formation of a single-phase structure for the composition Fe-8Cr-6Mn-5Mo-5Si-3.2C (wt.%), at relatively low cooling rates (≈103 K/s) and for large sample dimensions (2.85 mm). The single phase, which is likely to be the hcp ɛ-phase, was found to decompose into a finely distributed structure of bainite and carbides at ≈600 °C. The annealed structure showed very high hardness values (850 to 1200 HV), which could be exploited in the development of high-strength Fe-base materials.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. xii, 52 p.
Series
KTH/MSE, 2007:27
Keyword
Porous metals; Metal foams; Gas solubility; Fe-base alloys; Al-base alloys; M7C3 carbides; Al3Ti; Al3Fe; Rapid solidification; Metastable phases
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4428 (URN)978-91-7178-684-5 (ISBN)
Public defence
2007-06-15, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100809Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2010-08-09Bibliographically approved

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