Microstructural formations and phase transformation pathways in tantalum carbides
type: CreativeWork
description: Transition metal carbides have a large assortment of applications because of their high hardness, chemical resistance, and high melting temperatures. Tantalum carbide (TaC) and its sub-stoichiometric Ta2C and Ta4C3 phases have emerged as candidate materials for ultra-high temperature structural applications. A consequence of the high melting temperature is the limiting methods to fabricate near-net shape, near full density tantalum carbides. In general, hot-isostatic pressing (HIP) and/or arc melting/vacuum plasma spraying (VPS) of powders are the viable means of manufacturing. In HIP'ing, the phase formation is through solid-state reactions whereas arc melting/VPS involves rapid solidification. Additionally, the precipitation of multiple phases generates various orientation relationships that influence the grain morphology. Depending on carbon content, the grains were equiaxed, equiaxed with a cross-hatch pattern of thin laths of secondary phases, to acicular grains. The microstructures were quantified through a series of different 2D and 3D analytical techniques. To understand how these microstructures developed, a series of XTa:(1-X)C (0.5<X<1) atomic compositions have been fabricated by VPS and HIP processes that spanned the single phase TaC, multi-phase TaC+Ta4C3+Ta2C and single phase Ta2C fields. The results revealed that the grain size was constrained by either the larger as-sprayed grain sizes in the VPS process or the largest powder sizes that sintered in the HIP process. The equiaxed grains formed in the single phase materials because they did not have another phase which would dictate a low energy orientation relationship to change the grain morphology. The cross-hatch pattern in the equiaxed grains formed from the precipitation of the lower melting temperature Ta4C3 and Ta2C phases in the TaC matrix on the closed packed planes. Since the B1 TaC structure has multiple variants of these {111} planes, these precipitates formed on these different planes. The…
abstract: Transition metal carbides have a large assortment of applications because of their high hardness, chemical resistance, and high melting temperatures. Tantalum carbide (TaC) and its sub-stoichiometric Ta2C and Ta4C3 phases have emerged as candidate materials for ultra-high temperature structural applications. A consequence of the high melting temperature is the limiting methods to fabricate near-net shape, near full density tantalum carbides. In general, hot-isostatic pressing (HIP) and/or arc melting/vacuum plasma spraying (VPS) of powders are the viable means of manufacturing. In HIP'ing, the phase formation is through solid-state reactions whereas arc melting/VPS involves rapid solidification. Additionally, the precipitation of multiple phases generates various orientation relationships that influence the grain morphology. Depending on carbon content, the grains were equiaxed, equiaxed with a cross-hatch pattern of thin laths of secondary phases, to acicular grains. The microstructures were quantified through a series of different 2D and 3D analytical techniques. To understand how these microstructures developed, a series of XTa:(1-X)C (0.5<X<1) atomic compositions have been fabricated by VPS and HIP processes that spanned the single phase TaC, multi-phase TaC+Ta4C3+Ta2C and single phase Ta2C fields. The results revealed that the grain size was constrained by either the larger as-sprayed grain sizes in the VPS process or the largest powder sizes that sintered in the HIP process. The equiaxed grains formed in the single phase materials because they did not have another phase which would dictate a low energy orientation relationship to change the grain morphology. The cross-hatch pattern in the equiaxed grains formed from the precipitation of the lower melting temperature Ta4C3 and Ta2C phases in the TaC matrix on the closed packed planes. Since the B1 TaC structure has multiple variants of these {111} planes, these precipitates formed on these different planes. The…
author: Morris, Robert Allen
language: en_US
language: English
keywords: Engineering, Metallurgy, Materials science
date published: 2010
date modified: 2026-07-27T18:44:16Z
provider: University of Alabama
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Alabama Libraries