An Explanation of Microstructures in the Tantalum-Carbon System

Abstract

04Compositions in the tantalum-carbon system were prepared by carburizing high-purity tantalum wires. T h e microstructures so produced exhibit regions of a characteristic striated structure identical to those observed by earlier investigators. There are disparities in the literature as to the origin of such structures in the tantalum-carbon system. They have been variously described as "twins," "striated structure," "precipitate," and' "structure of unknown origin." This paper presents conclusive evidence that the structures in question are the result of precipitation on cooling. I n addition, a coherent precipitation model is applied in which it is shown that the lattice relationship { 0 0 0 1 )~~, c~~( 1 1 1 }~~~ can exist with less than 0.5% misfit. This relationship is shown to completely explain the

Atomic and vacancy ordering in carbide ζ-Ta4C3−x (0.28⩽x⩽0.40) and phase equilibria in the Ta–C system

“…Obviously, annealing duration was not enough for reaching of equilibrium state in which samples contain only two phases z-Ta 4 C 3Àx and TaC y . Note that three-phase samples containing cubic and hexagonal carbides along with z-Ta 4 C 3Àx were obtained in previous studies [3,[6][7][8][9]13,14]. Analysis performed suggests that the set of diffraction reflections from the z-Ta 4 C 3Àx phase, which is observed in the XRD pattern, corresponds to a trigonal (space group R3m) unit cell.…”

“…According to refinement results, in a unit cell of the z-Ta 4 C 3Àx phase positions 6(c) with the coordinates (0, 0, 0.1273(6)) and (0, 0, 0.291(10)) are occupied twice by twelve atoms Ta, positions 6(c) with the coordinates (0, 0, 0.4169 (9)) are occupied by carbon atoms. Positions 3(a) and 3(b) with the coordinates (000) and (00 1 2 ) correspond to lattice sites, on which the distribution of atoms C can be disordered or ordered (Fig.…”

“…The z-phase composition was defined as Ta 3 C 2 by Rudy et al [4,5]. The researchers [6][7][8][9] with carbon and found that the z-phase precipitated in the gap between layers of nonstoichiometric cubic TaC y and hexagonal Ta 2 C carbides.…”

Bonding Effects on the Slip Differences in theB1Monocarbides

“…Both groups of TMMCs form the B1, or rocksalt structure, which is an array of FCC metal atoms with the carbon atoms filling every octahedral interstice [2,3]. The bonding in these materials is a mix of covalent, metallic and ionic resulting in high hardness as well as good thermal and electrical conductivity [4][5][6][7].…”

Epitaxial growth of tantalum carbides by low carbon flow carburizing

“…This property makes it the coating material of choice for cutting tool inserts [2]. This material has also been extensively studied for its refractory properties [3,4] on account of its high melting temperature of nearly 4270 K [5,6].…”