ζ‐Ta 4 C 3− x : A High Fracture Toughness Carbide with Rising‐Crack‐Growth‐Resistance (R‐Curve) Behavior
The microstructures and mechanical properties of tantalum carbides containing predominantly the ζ‐Ta 4 C 3− x phase are compared with the properties of the monocarbide (γ‐TaC) and the hemicarbide (α‐Ta 2 C) and two‐phase composites. It is shown that a Ta and γ‐TaC powder mixture corresponding to a C...
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Published in | Journal of the American Ceramic Society Vol. 98; no. 8; pp. 2601 - 2608 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
01.08.2015
|
Online Access | Get full text |
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Summary: | The microstructures and mechanical properties of tantalum carbides containing predominantly the ζ‐Ta
4
C
3−
x
phase are compared with the properties of the monocarbide (γ‐TaC) and the hemicarbide (α‐Ta
2
C) and two‐phase composites. It is shown that a Ta and γ‐TaC powder mixture corresponding to a C/Ta at. ratio of 0.66 can be hot‐pressed (1800°C, 2 h) to obtain ~95 wt% of ζ‐Ta
4
C
3−
x
with a density of 98% of theoretical. This material has an attractive combination of high fracture toughness (13.8 ± 0.2 MPa√m) and fracture strength (759 ± 24 MPa) with modest hardness (5.6 ± 0.5 GPa). The fracture toughness and strength measured for this material were the highest among all the materials with C/Ta ratio ranging from 0.5 (hemicarbide) to 1.0 (monocarbide). It is also shown that a material containing 86 wt% ζ‐Ta
4
C
3−
x
can be consolidated by pressureless sintering of a hydrogenated Ta and γ‐TaC powder mixture without significant drop in density (97% of theoretical) or mechanical properties (13.4 ± 0.2 MPa√m, 700 ± 20 MPa, 6.0 ± 0.4 GPa). Materials containing high weight fraction of the ζ‐Ta
4
C
3−
x
phase exhibited rising crack‐growth‐resistance (
R
‐curve) behavior. Optical and scanning electron microscope observations suggested crack‐face bridging was the dominant toughening mechanism. The crack‐bridging ligaments were lamellae of the basal planes of the ζ‐Ta
4
C
3−
x
phase produced by their easy cleavage. The thickness of the lamellae ranged from 40 to 2000 nm, significantly less than the grain size. |
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ISSN: | 0002-7820 1551-2916 |
DOI: | 10.1111/jace.13635 |