Microstructure of NbSi2/SiC nanocomposite coating formed on Nb substrate

Keun Hyung Son, Jin Kook Yoon, Jun Hyun Han, Gyeung Ho Kim, Jung Mann Doh, Seong Rae Lee

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)

Abstract

The microstructure of a NbSi2/α-SiC nanocomposite coating formed by a pack siliconizing process of Nb-carbide layers at 1100°C, which had already been formed on the surface of a Nb substrate by a carburizing process, was investigated. The Nb-carbide layers formed by the carburizing process at 1400°C using a gas mixture of CH4-H2 consisted of two layers, i.e., an inner layer of Nb2C and an outer layer of NbC. While the monolithic NbSi2 coating showed a typical columnar microstructure perpendicular to the Nb substrate, the NbSi 2/α-SiC nanocomposite coating formed by the solid-state displacement reaction of the NbC layer by Si was composed of equiaxed NbSi 2 grains with an average size of 67-134 nm and the α-SiC particles with an average size of 45-60 nm. The morphology of the α-SiC particles exhibited an oblate-spheroidal shape and were mostly located at the grain boundaries of NbSi2. The nanocomposite coating formed by the solid-state displacement reaction of the Nb2C layer by Si showed a lamella microstructure. The average lamella diameters of the NbSi2 grains and the α-SiC particles were about 250 and 60 nm, respectively. The volume percentage of the α-SiC particles ranged from 17.3 to 31.1% with respect to the carbon concentration in Nb-carbide layers. No cracks were observed in the NbSi2/α-SiC nanocomposite coating, indicating that its thermal expansion coefficient was close to that of the Nb substrate.

Original languageEnglish
Pages (from-to)185-191
Number of pages7
JournalJournal of Alloys and Compounds
Volume395
Issue number1-2
DOIs
Publication statusPublished - 2005 May 31

Keywords

  • Carburizing and siliconizing
  • Microstructure
  • Nanocomposite coating
  • NbSi/β-SiC

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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