Strength of single‐phase high‐entropy carbide ceramics up to 2300°C

TLDR

The study investigates the mechanical properties of single‑phase (Hf,Zr,Ti,Ta,Nb)C high‑entropy carbide ceramics. The ceramics were fabricated by carbothermal reduction at 1600 °C followed by hot pressing at 1900 °C to achieve >99 % relative density and ~0.9 µm grains, and flexural strength loss above 1800 °C was attributed to reduced dislocation density and increased dislocation motion. The HEC ceramics exhibited a Vickers hardness of 25 GPa, Young’s modulus of 450 GPa, fracture toughness of 3.5 MPa·m¹/², and a room‑temperature flexural strength of 421 MPa, while maintaining >400 MPa up to 1800 °C and decreasing to 93 MPa at 2300 °C, with no change in density or grain size, marking the first reported high‑temperature flexural strengths for this material.

Abstract

Abstract The mechanical properties of single‐phase (Hf,Zr,Ti,Ta,Nb)C high‐entropy carbide (HEC) ceramics were investigated. Ceramics with relative density >99% and an average grain size of 0.9 ± 0.3 µm were produced by a two‐step process that involved carbothermal reduction at 1600°C and hot pressing at 1900°C. At room temperature, Vickers hardness was 25.0 ± 1.0 GPa at a load of 4.9 N, Young's modulus was 450 GPa, chevron notch fracture toughness was 3.5 ± 0.3 MPa·m 1/2 , and four‐point flexural strength was 421 ± 27 MPa. With increasing temperature, flexural strength stayed above ~400 MPa up to 1800°C, then decreased nearly linearly to 318 ± 21 MPa at 2000°C and to 93 ± 10 MPa at 2300°C. No significant changes in relative density or average grain size were noted after testing at elevated temperatures. The degradation of flexural strength above 1800°C was attributed to a decrease in dislocation density that was accompanied by an increase in dislocation motion. These are the first reported flexural strengths of HEC ceramics at elevated temperatures.