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Microstructure evolution during phase separation in Ti-Zr-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.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0003-1102-4342
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2016 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 61, 238-248 p.Article in journal (Refereed) Published
Abstract [en]

(Ti,Zr)C powder was synthesized by carbothermal reduction and subsequently aged at 1150–2000 °C. The phase composition and microstructure was investigated using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and electron backscatter diffraction. It was found that the as-synthesized (Ti,Zr)C particles have a concentration gradient with a higher concentration of Ti at the surface of the particles. Furthermore, during aging the (Ti,Zr)C decomposes into Ti-rich and Zr-rich lamellae. During aging at 1400 and 1800 °C for 10 h, most Zr-rich and Ti-rich domains precipitate at grain boundaries, inheriting the crystal orientation of the parent grain behind the growth front. When the precipitate grows into another (Ti,Zr)C grain, that grain adopts the same crystal orientation as the parent grain. The crystallographic misorientation between adjacent lamellae is 0–5°. Based on these microstructural observations it is hypothesized that the mechanism of decomposition is discontinuous precipitation.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 61, 238-248 p.
Keyword [en]
Carbides, Discontinuous precipitation, Electron backscatter diffraction, Energy-dispersive X-ray spectroscopy, Phase separation, Backscattering, Carbothermal reduction, Electron diffraction, Energy dispersive spectroscopy, Grain boundaries, Grain growth, Microstructure, Precipitation (chemical), Scanning electron microscopy, X ray diffraction, X ray spectroscopy, Concentration gradients, Electron back scatter diffraction, Energy dispersive X ray spectroscopy, Mechanism of decomposition, Micro-structural observations, Micro-structure evolutions, Mis-orientation, Crystal orientation
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-195185DOI: 10.1016/j.ijrmhm.2016.09.019ISI: 000388048300032Scopus ID: 2-s2.0-84989814061OAI: oai:DiVA.org:kth-195185DiVA: diva2:1053104
Funder
VINNOVA, 2014-03392
Note

QC 20161208

Available from: 2016-12-08 Created: 2016-11-02 Last updated: 2017-06-28Bibliographically 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. 43 p.
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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Supervisors
Note

QC 20170529

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

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