ZrB2ceramics were prepared by in‐situ reaction hot pressing of ZrH2and B. Additions of carbon and excess boron were used to react with and remove the residual oxygen present in the starting powders. Additions of tungsten were utilized to make a ZrB2‐4 mol%W ceramic, while a change in the B/C ratio was used to produce a ZrB2‐10 vol% ZrC ceramic. All three compositions reached near full density. The baseline ZrB2and ZrB2–ZrC composition contained a residual oxide phase and ZrC inclusions, while the W‐doped composition contained residual carbon and a phase that contained tungsten and boron. All three compositions exhibited similar values for flexure strength (~520 MPa), Vickers hardness (~15 GPa), and elastic modulus (~500 to 540 GPa). Fracture toughness was about 2.6 MPa m1/2for the W‐doped ZrB2compared to about 3.8 MPa m½for the ZrB2and ZrB2–ZrC ceramics. This decrease in fracture toughness was accompanied by an observed absence of crack deflection in the W‐doped ZrB2compared with the other compositions. The study demonstrated that reaction‐hot‐pressing can be used to fabricate ZrB2based ceramics containing solid solution additives or second phases with comparable mechanical properties.
Zirconium carbide (ZrC) powder, batched to a ratio of 0.98 C/Zr, was prepared by carbothermal reduction of ZrO2with carbon black. Nominally phase‐pure ZrC powder had a mean particle size of 2.4 μm. The synthesized powder was hot‐pressed at 2150°C to a relative density of > 95%. The mean grain size was 2.7 ± 1.4 μm with a maximum observed grain size of 17.5 μm. The final hot‐pressed billets had a C/Zr ratio of 0.92, and oxygen content of 0.5 wt%, as determined by gas fusion analysis. The mechanical properties of ZrC0.92O0.03were measured at room temperature. Vickers’ hardness decreased from 19.5 GPa at a load of 0.5 kgf to 17.0 GPa at a load of 1 kgf. Flexural strength was 362.3 ± 46 MPa, Young's modulus was 397 ± 13 MPa, and fracture toughness was 2.9 ± 0.1 MPa•m1/2. Analysis of mechanical behavior revealed that the largest ZrC grains were the strength‐limiting flaw in these ceramics.
more » « less- Award ID(s):
- 1742086
- NSF-PAR ID:
- 10453522
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 104
- Issue:
- 1
- ISSN:
- 0002-7820
- Page Range / eLocation ID:
- p. 413-418
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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