The mechanical properties of a (Hf,Mo,Nb,Ta,W,Zr)B2 high‐entropy ceramic were measured at room temperature. A two‐step synthesis process was utilized to produce the (Hf,Mo,Nb,Ta,W,Zr)B2 ceramics. The process consisted of a boro/carbothermal reduction reaction followed by solid solution formation and densification through spark plasma sintering. Nominally, phase pure (Hf,Mo,Nb,Ta,W,Zr)B2 was sintered to near full density (8.98 g/cm3) at 2000°C. The mean grain size was 6 ± 2 µm with a maximum grain size of 17 µm. Flexural strength was 528 ± 53 MPa, Young's modulus was 520 ± 12 GPa, fracture toughness was 3.9 ± 1.2 MPa·m1/2, and hardness (HV0.2) was 33.1 ± 1.1 GPa. A Griffith‐type analysis determined the strength limiting flaw to be the largest grains in the microstructure. This is one of the first reports of a variety of mechanical properties of a six‐component high‐entropy diboride.
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The mechanical properties of a nominally phase pure ZrB 2 ceramic were measured up to 2300°C in an argon atmosphere. ZrB 2 was hot pressed at 2000°C utilizing borothermally synthesized powder from high purity ZrO 2 and B raw materials. The relative density of the ceramics was about 95% with an average ZrB 2 grain size of 8.8 µm.The room temperature flexural strength was 447 MPa, with strength decreasing to 196 MPa at 1800°C, and then increasing to 360 MPa at 2300°C. The strength up to 1800°C was likely controlled by a combination of effects: surface damage from oxidation of the specimens, stress relaxation, and decreases in the elastic modulus.The strength above 1800°C was controlled by flaws in the range consistent with sizes of the maximum ZrB 2 grain size and the largest pores. Fracture toughness was 2.3 MPa•m 1/2 at room temperature, increasing to 3.1 MPa•m 1/2 at 2200°C. The use of higher purity starting materials improved the mechanical behavior in the ultra-high temperature regime compared to previous studies.
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