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Powder-metallurgical synthesis and aging of (V,Nb)C and (V,Ta)C
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0003-1102-4342
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0003-3598-2465
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The ternary carbides (V,Nb)C and (V,Ta)C have been synthesized by heat-treating powder mixtures of the corresponding binary carbides. The effect of different mixing and milling conditions as well as the addition of small amounts of Fe powder on the resulting carbide microstructure after synthesis was investigated. The as-synthesized carbides were aged at 900 and 1200 °C, which are inside the miscibility gap for both systems, to study the decomposition. The microstructure after aging was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and electron backscatter diffraction. It was found that (V,Nb)C with small additions of Fe decomposed in a way that resembles discontinuous precipitation upon aging at 1200 °C. (V,Ta)C with and without additions of Fe was found to decompose upon aging at 1200 °C, but giving a different morphology compared to (V,Nb)C. The hardness of both as-synthesized and aged carbides was measured using nano-indentation and the hardness was found to be 26.5 ± 1 GPa and 30.2 ± 1.3 GPa for (V,Nb)C and (V,Ta)C respectively. The high hardness was found to be maintained in (V,Nb)C after decomposing into V-rich and Nb-rich lamellae. 

Keywords [en]
ternary transition metal carbide, phase separation, powder metallurgy, scanning electron microscopy, nano-indentation
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-207838OAI: oai:DiVA.org:kth-207838DiVA, id: diva2:1098737
Note

QC 20170529

Available from: 2017-05-26 Created: 2017-05-26 Last updated: 2017-05-29Bibliographically approved
In thesis
1. Powder-metallurgical processing and phase separation in ternary transition metal carbides
Open this publication in new window or tab >>Powder-metallurgical processing and phase separation in ternary transition metal carbides
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ternary transition metal cubic carbides have high hardness and are potential carbides in cemented carbide and cermet tools, as well as hard coatings used to improve metal cutting performance. In the present work, (Ti,Zr)C, (V,Nb)C, and (V,Ta)C ternary cubic carbides were synthesized using traditional powder-metallurgical methods. The effect of synthesis temperature and starting materials on synthesis is investigated, and the microstructure evolution during aging is studied. (Ti,Zr)C was found to decompose into lamellae upon aging at the temperature range from 1150 to 1800 °C. A similar microstructure was observed in (V,Ta)C and (V,Nb)C- 0.5 wt% Fe. All of these structures were found to form through discontinuous precipitation.The grain misorientation distribution of (Ti,Zr)C aged at 1400 °C is investigated. It was found that decomposition tends to occur at high-angle grain boundaries above 25°. The hardness of as-synthesized (Ti,Zr)C powder was found to be 41±6 GPa. Fully decomposed (Ti,Zr)C particles were found to be slightly harder than the undecomposed counterpart. On the other hand, in (V,Nb)C-0.5 wt% Fe, the decomposed structure formed upon aging at 1200 °C was found to have a hardness of 26±2 GPa, which is basically the same as the unaged alloy.Furthermore, the sintering behavior of (Ti,Zr)C with WC-Co is investigated. There are two γ-phases in the final microstructure, one TiC-rich and one ZrC-rich. (Ti,Zr)C was found to decompose at an early stage of sintering, and the final grain size of WC and the two γ-phases was found to be 10% smaller than that in a reference WC-TiC-ZrC-Co composite.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. p. 43
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-207839 (URN)978-91-7729-439-9 (ISBN)
Public defence
2017-06-15, B2, Brinellvägen 23, Stockholm, 10:00 (English)
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Note

QC 20170529

Available from: 2017-05-29 Created: 2017-05-26 Last updated: 2017-05-30Bibliographically approved

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Odqvist, Joakim

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