Ultra‐High Temperature Mechanical Properties of a Zirconium Diboride–Zirconium Carbide Ceramic

Abstract

The mechanical properties of a ZrB2‐10 vol% ZrC ceramic were measured up to 2300°C in an argon atmosphere. Dense billets of ZrB2‐9.5 vol% ZrC‐0.1 vol% C were produced by hot‐pressing at 1900°C. The ZrB2 grain size was 4.9 μm and ZrC cluster size was 1.8 μm. Flexure strength was 695 MPa at ambient, decreasing to 300 MPa at 1600°C, increasing to 345 MPa at 1800°C and 2000°C, and then decreasing to 290 MPa at 2200°C and 2300°C. Fracture toughness was 4.8 MPa·m½ at room temperature, decreasing to 3.4 MPa·m½ at 1400°C, increasing to 4.5 MPa·m½ at 1800°C, and decreasing to 3.6 MPa·m½ at 2300°C. Elastic modulus calculated from the crosshead displacement was estimated to be 505 GPa at ambient, relatively unchanging to 1200°C, then decreasing linearly to 385 GPa at 1600°C, more slowly to 345 GPa at 2000°C, and then more rapidly to 260 GPa at 2300°C. Surface flaws resulting from machining damage were the critical flaw up to 1400°C. Above 1400°C, plasticity reduced the stress at the crack tip and the surface flaws experienced subcritical crack growth. Above 2000°C, microvoid coalescence ahead of the crack tip caused failure.

Super-strong materials for temperatures exceeding 2000 °C

“…1 and, compared to previously published data on other ZrB 2 -based ceramics4789111217. Our ceramic possesses the highest strength ever reported for a ZrB 2 -based ceramic at temperatures above 1500 °C.…”

“…Our ceramic possesses the highest strength ever reported for a ZrB 2 -based ceramic at temperatures above 1500 °C. The room temperature strength of ZS3-WC was 630 ± 76 MPa, similar to other fully dense ZrB 2 or HfB 2 ceramics containing W-compounds or other refractory sintering additives37891011. Increasing the testing temperature to 1500 °C, the strength was ~700 MPa in either air or argon.…”

“…Increasing the testing temperature to 1500 °C, the strength was ~700 MPa in either air or argon. Remarkably, 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 ZrB 2 -based ceramics at those temperatures789101112.…”

“…Flexural strength as a function of temperature for the highest strength ZrB 2 -ceramics41217, or tested at the highest temperatures in air or Argon78911. pw: present work.…”

“…These studies show that the strength of ceramics containing 20–30 vol% SiC is generally retained, or even increased, from room temperature up to 1000 °C. Strengths range between 500 and 700 MPa due to the formation of a continuous silica-based-glass capable of healing surface flaws7891011. However, by 1500 °C, strength decreases to 200–340 MPa, owing to coalescence of micro-voids formed at triple junctions, softening of the grain boundary phases, and grain coarsening456.…”