Phase stability and microstructural formations in the niobium carbides. Issue 15 (December 2018)

• Record Type: Journal Article
• Authors: Smith, Chase J.; Weinberger, Christopher R.; Thompson, Gregory B.
• Is Part Of: Journal of the European Ceramic Society. Volume 38:Issue 15(2018)
• Page Start: 4850
• Page End: 4866
• Publication Date: 2018-12
• Subjects: Transmission electron microscopy (TEM) -- Transition metal carbides -- Niobium carbide -- Precipitation -- Hardness; Ceramic materials -- Periodicals; Composite materials -- Periodicals; Matériaux céramiques -- Périodiques; Composites -- Périodiques; Ceramic materials; Composite materials; Periodicals; Electronic journals; 666.05
• DOI: 10.1016/j.jeurceramsoc.2018.06.041
• Languages: English
• ISSNs: 0955-2219

Abstract

Abstract: The phase stability and microstructural formations for a series of hot isostatically pressed (HIP) NbCx compositions was investigated. Based on the composition, single-phase B1 (Fm 3 ¯ m) NbC or (P 3 ¯ 1m) β−Nb2 C equiaxed grains were observed as well as β-Nb2 C lath precipitation within NbC. Particular discussion is given to the complexities of X-ray and electron diffraction for proper identification for the various poly-types of Nb2 C that have been computationally predicted. The phase transformation pathways for these microstructures was revealed by a NbC-Nb diffusion couple from the HIP powders. The migration of vacancies towards the NbC side resulted in a refinement of the NbC grains whereas carbon's migration into the Nb formed an uniform and distinct reaction front with a mixture of β-Nb2 C and Nb grains. This latter microstructure suggests carbon's reaction through the matrix grain is as significant in the conversion process as is the precipitation of β-Nb2 C at the grain boundaries.