Flexural strength of (Hf,Nb,Ta,Ti,Zr)B ₂ –(Hf,Nb,Ta,Ti,Zr)C high‐entropy dual‐phase ceramics

Abstract The room and elevated temperature flexural strengths were measured for (Hf,Nb,Ta,Ti,Zr)B 2 –(Hf,Nb,Ta,Ti,Zr)C high‐entropy dual‐phase ceramics. The fracture of ceramics originated from two distinct flaw populations that were either surface defects introduced during specimen preparation or volume defects introduced during processing. The average strength at room temperature was 638 ± 94 MPa with individual bars strengths as high as ∼800 MPa. At 1800°C, average strength increased to 786 ± 265 MPa with individual bar strengths as high as ∼1050 MPa. Above 1800°C, creep dominated resulting in deformation of the bars without fracture. The fracture mode changed from completely transgranular at room temperature to mixed mode with increasing temperature and then to completely intergranular at 1800°C. The room temperature strength was higher than the reported strengths of the individual constituent phases, which was attributed to fine grain sizes. At elevated temperatures, the increase in strength could be due to the relaxation of stresses in addition to the grain size. To our knowledge, this is the first study reporting the flexural strength of (Hf,Nb,Ta,Ti,Zr)B 2 –(Hf,Nb,Ta,Ti,Zr)C dual‐phase ceramics at elevated temperatures.