High-temperature stability of {alpha}-Ta{sub 4}AlC{sub 3}

Journal Article · Fri Jul 15 04:00:00 EDT 2011 · Materials Research Bulletin

DOI:https://doi.org/10.1016/J.MATERRESBULL.2011.03.005· OSTI ID:22212202

Eklund, Per; Lu, Jun ^[1]; Spencer, Charles B. ^[2]; Hultman, Lars ^[1]; Barsoum, Michel W. ^[2]

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1. Department of Physics, Chemistry and Biology (IFM), Linkoeping University, SE-581 83 Linkoeping (Sweden)
2. Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104 (United States)

Graphical abstract: In this study, stability of {alpha}-Ta{sub 4}AlC{sub 3} is investigated to test a hypothesized thermodynamically driven {alpha}-{beta} phase transformation. It is found that the {alpha} phase is stable up to 1600 {sup o}C, with impurities and point defects most likely increasing the stability of the {alpha}-Ta{sub 4}AlC{sub 3}. Highlights: {yields} Cold-pressed {alpha}-Ta{sub 4}AlC{sub 3} powders are annealed up to 1750 {sup o}C to test first-principles predictions of {alpha}-{beta} phase-stability reversal at 1600 {sup o}C. {yields} The {alpha}-Ta{sub 4}AlC{sub 3} samples are stable up to 1600 {sup o}C, with no indications of any {alpha}-{beta} transformation. {yields} Transmission electron microscopy shows zig-zag stacking sequence characteristic of {alpha}-Ta{sub 4}AlC{sub 3}, as well as tantalum oxide impurities. {yields} The XRD patterns suggest that defects such as vacancies or antisites may increase the stability of {alpha}-Ta{sub 4}AlC{sub 3}. -- Abstract: Cold-pressed {alpha}-Ta4AlC3 powders were annealed up to 1750 {sup o}C to test first-principles predictions of {alpha}-{beta} phase-stability reversal at 1600 {sup o}C. Up to 1600 {sup o}C, the {alpha}-Ta{sub 4}AlC{sub 3} samples were stable with no indications of any {alpha}-{beta} transformation, as shown by the strong characteristic X-ray diffraction peaks of {alpha}-Ta{sub 4}AlC{sub 3} and the zigzag stacking observed by transmission electron microscopy. These results show that, in this experimental situation, high temperature alone is not sufficient to cause the {alpha}-{beta} transformation.

• OSTI ID: 22212202
• Journal Information: Materials Research Bulletin, Journal Name: Materials Research Bulletin Journal Issue: 7 Vol. 46; ISSN MRBUAC; ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
PHASE STABILITY
PHASE TRANSFORMATIONS
POWDERS
TANTALUM OXIDES
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION