Elevated Temperature Strength Enhancement of ZrB₂–30 vol% SiC Ceramics by Postsintering Thermal Annealing

Abstract

The mechanical properties of dense, hot‐pressed ZrB2–30 vol% SiC ceramics were characterized from room temperature up to 1600°C in air. Specimens were tested as hot‐pressed or after hot‐pressing followed by heat treatment at 1400°C, 1500°C, 1600°C, or 1800°C for 10 h. Annealing at 1400°C resulted in the largest increases in flexure strengths at the highest test temperatures, with strengths of 470 MPa at 1400°C, 385 MPa at 1500°C, and 425 MPa at 1600°C, corresponding to increases of 7%, 8%, and 12% compared to as hot‐pressed ZrB2–SiC tested at the same temperatures. Thermal treatment at 1500°C resulted in the largest increase in elastic modulus, with values of 270 GPa at 1400°C, 240 GPa at 1500°C, and 120 GPa at 1600°C, which were increases of 6%, 12%, and 18% compared to as hot‐pressed ZrB2–SiC. Neither ZrB2 grain size nor SiC cluster size changed for these heat‐treatment temperatures. Microstructural analysis suggested additional phases may have formed during heat treatment and/or dislocation density may have changed. This study demonstrated that thermal annealing may be a useful method for improving the elevated temperature mechanical properties of ZrB2‐based ceramics.

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.…”