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The oxidation behavior of three different ZrB2 -based ceramics, a monolithic ZrB2 and two ZrB2­normalSiC composites, was studied up to 1350°C and under isothermal conditions at 1120°C for 20 h. Oxidation kinetics and microstructural changes in the oxidized specimens indicate that the monolithic ZrB2 has low thermal stability. On the contrary, the introduction of SiC particles markedly improves oxidation resistance due to the formation of an adherent and protective borosilicate glass layer that coats the sample surface, effectively limiting the inward diffusion of oxygen toward the reaction interface. The influence of the secondary grain boundary phases on oxidation is discussed. © 2003 The Electrochemical Society. All rights reserved.

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This work investigated suitability and efficacy of the sintering technique known as spark plasma sintering to produce ultra‐high‐temperature‐based Hf and Zr borides. Ceramic–matrix composites in the systems HfB2–SiC, ZrB2–MoSi2, and ZrB2–ZrC–SiC were processed by spark plasma sintering and hot pressing. The effects of processing were evaluated comparing the materials microstructure and properties. Compared with hot‐pressing technique, spark plasma sintering offers the great advantage to fabricate successfully in short time (i.e., cuts in costs) poorly sinterable powder compositions without the help of any sintering activators.

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A ZrB2‐based composite was fully densified by pressureless sintering at 1850°C with addition of 20 vol% MoSi2. The microstructure was very fine, with mean dimensions of ZrB2 grains around 2.5 μm. The four‐point flexural strength in air was in excess of 500 MPa up to 1500°C.

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