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On the effect of nitrogen, hydrogen and cooling rate on the solidification and pore formation in Fe-base and Al-base alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
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 [en]
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: urn:nbn:se:kth:diva-4428ISBN: 978-91-7178-684-5 (print)OAI: oai:DiVA.org:kth-4428DiVA: diva2:12279
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
List of papers
1. Production of Fe-Cr-C base foam: theoretical considerations and partical fabrication
Open this publication in new window or tab >>Production of Fe-Cr-C base foam: theoretical considerations and partical fabrication
2005 (English)In: Proceedings of the Symposium on "Cellular Metals and Polymers" / [ed] Singer,R.F., Körner, C., Altstädt, V., Münstedt, H., Zürich: Trans Tech Publications , 2005, 49-52 p.Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Zürich: Trans Tech Publications, 2005
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7304 (URN)
Conference
Symposium on 'Cellular Metals and Polymers', Fürth, Germany, October 2004
Note

QC 20100809

Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2012-10-23Bibliographically approved
2. Study on the production of Fe–Cr–Mn–C–Si foam by nitrogen solubility difference between the liquid and solid phases
Open this publication in new window or tab >>Study on the production of Fe–Cr–Mn–C–Si foam by nitrogen solubility difference between the liquid and solid phases
2005 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413-414, 533-537 p.Article in journal (Refereed) Published
Abstract [en]

The feasibility of the production of Fe-base metallic foam by using the nitrogen solubility difference between the liquid and austenite phases has been studied in the Fe-Cr-Mn-C-Si system. Compositions showing a suitable solubility gap for precipitation of gas pores upon solidification have been derived by thermodynamic calculations of the nitrogen solubility in the liquid and solid phases, using the interaction parameters of nitrogen. Small amount of foams were produced for different compositions. The foaming involved dissolution of chromium nitrides into the melt and subsequent quenching. Four different compositions were tested: by varying the C content between 2 and 6 wt.%, the effect of the primary carbides on the foam microstructure could be studied. The presence of those carbides appears as an important element for the promotion of the pore nucleation and the prevention of pore coalescence. The addition of SiO2 powder in some experiments illustrated the beneficial effect of a nucleating agent to reach a homogeneous distribution of the gas pores.

Keyword
Fe-base foam; Metallic foam; Nitrogen solubility; Nucleation; Chromium compounds; Composition effects; Dissolution; Foams; Metallographic microstructure; Nucleation; Phase composition; Precipitation (chemical); Quenching; Solidification; Solubility; Thermodynamic properties; Chromium nitrides; Gas pores; Metallic foam; Nitrogen solubility; Iron alloys; nucleation
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7305 (URN)10.1016/j.msea.2005.08.152 (DOI)000234202900089 ()2-s2.0-29544436164 (Scopus ID)
Note
QC 20100809Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2017-12-14Bibliographically approved
3. Variation of nitrogen solubility and mechanism of pore formation during production of porous Fe-Cr-Mn-Si-C material
Open this publication in new window or tab >>Variation of nitrogen solubility and mechanism of pore formation during production of porous Fe-Cr-Mn-Si-C material
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.

Keyword
porous metals; nitrogen solubility; pore formation; supersaturation; M7C3 carbides ; UNIDIRECTIONAL SOLIDIFICATION; IRON; FABRICATION; ATMOSPHERE; ALLOYS; STEEL
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7306 (URN)10.1179/136404607X212068 (DOI)000250924600008 ()2-s2.0-36048985431 (Scopus ID)
Note
QC 20100809. Uppdaterad från Accepted till Published 20100809.Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2017-12-14Bibliographically approved
4. Synthesis and structural characterisation of porous Al-Fe and Al-Ti materials obtainted by hydrogen solubility variation
Open this publication in new window or tab >>Synthesis and structural characterisation of porous Al-Fe and Al-Ti materials obtainted by hydrogen solubility variation
2007 (English)Report (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH, 2007
Series
KTH/MSE-07/29-SE-CER/ART, 2007:29
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7307 (URN)
Note
QC 20100809. Även publicerad i förkortad version i "Proceedings of the 5th Decennial International Conference on Solidification Processing".Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2010-08-09Bibliographically approved
5. Uniaxial compression testing of porous Al-Fe and Al-Ti materials synthesized by water vapor dissolution
Open this publication in new window or tab >>Uniaxial compression testing of porous Al-Fe and Al-Ti materials synthesized by water vapor dissolution
2007 (English)Report (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH, 2007
Series
KTH/MSE-07/30-SE-CER/ART, 2007:30
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7308 (URN)
Note
QC 20100809Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2010-08-09Bibliographically approved
6. Rapid solidification behavior of Fe-Cr-Mn-Mo-Si-C alloys
Open this publication in new window or tab >>Rapid solidification behavior of Fe-Cr-Mn-Mo-Si-C alloys
2007 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 38, no 6, 917-926 p.Article in journal (Refereed) Published
Abstract [en]

The rapid solidification behavior of alloys in the Fe-Cr-Mn-Mo-Si-C system was investigated for different compositions and cooling rates. The C content was varied and alloying additions of Mo and B were studied with respect to their effect on the microstructure. The alloys were cast as either melt-spun ribbons or as 1-mm-thick plates after levitation or as rods 2 to 4 mm in diameter by injection into copper molds. A homogeneous single-phase structure was obtained for the alloy of composition 72.8Fe-8Cr-6Mn-5Si-5Mo-3.2C (wt pct), for a sample diameter of 2.85 mm, at a cooling rate of approximate to 1100 K/s. The single-phase structure was identified as a metastable solid solution, exhibiting the characteristics of the e phase. Upon reheating, decomposition of the single-phase structure into fine bainite plates and secondary carbides was observed between 600 degrees C and 700 degrees C. The annealed structure obtained showed high hardness values (> 850 HV).

Keyword
bulk metallic glasses; amorphous-alloys; epsilon-phase; steel
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-7309 (URN)10.1007/s11663-007-9108-4 (DOI)000251925700009 ()2-s2.0-37449031278 (Scopus ID)
Note
QC 20100805Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2017-12-14Bibliographically approved

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