Abstract
Ceramics based on group IV-V transition metal borides and carbides possess melting points above 3000 °C, are ablation resistant and are, therefore, candidates for the design of components of next generation space vehicles, rocket nozzle inserts, and nose cones or leading edges for hypersonic aerospace vehicles. As such, they will have to bear high thermo-mechanical loads, which makes strength at high temperature of great importance. While testing of these materials above 2000 °C is necessary to prove their capabilities at anticipated operating temperatures, literature reports are quite limited. Reported strength values for zirconium diboride (ZrB2) ceramics can exceed 1 GPa at room temperature, but these values rapidly decrease, with all previously reported strengths being less than 340 MPa at 1500 °C or above. Here, we show how the strength of ZrB2 ceramics can be increased to more than 800 MPa at temperatures in the range of 1500–2100 °C. These exceptional strengths are due to a core-shell microstructure, which leads to in-situ toughening and sub-grain refinement at elevated temperatures. Our findings promise to open a new avenue to designing materials that are super-strong at ultra-high temperatures.
Highlights
Ceramics based on group IV-V transition metal borides and carbides possess melting points above 3000 °C, are ablation resistant and are, candidates for the design of components of generation space vehicles, rocket nozzle inserts, and nose cones or leading edges for hypersonic aerospace vehicles
We report the flexural strength at temperatures up to 2100 °C for a ZrB2 ceramic containing WC and discontinuous SiC particles
Ceramics tested in either air or argon had a combination of favorable features that prevented the decrease in strength that typically has been observed as temperature increased
Summary
The strength of ZS3-WC as a function of temperature is plotted in Fig. 1 and, compared to previously published data on other ZrB2-based ceramics[4,7,8,9,11,12,17]. Our ceramic possesses the highest strength ever reported for a ZrB2-based ceramic at temperatures above 1500 °C. The ceramic had average strengths of 836 ± 103 MPa at 1800 °C and 660 ± 123 MPa at 2100 °C, which are approximately double the highest previously reported values for ZrB2-based ceramics at those temperatures[7,8,9,10,11,12]. Fracture toughness measured by chevron notched beam method at room temperature was 3.7 ± 0.9 MPa · √m. When we tested this property at 1500 °C we did not observe a substantial increase: 3.455 ± 0.4 MPa · √min air and 4.6 ± 0.5 MPa·√m, when measured in Argon atmosphere
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