Mechanical properties of borothermally synthesized zirconium diboride at elevated temperatures

The mechanical properties of a nominally phase pure ZrB2 ceramic were measured up to 2300 degrees C in an argon atmosphere. ZrB2 was hot pressed at 2000 degrees C utilizing borothermally synthesized powder from high purity ZrO2 and B raw materials. The relative density of the ceramics was about 95% with an average ZrB2 grain size of 8.8 mu m. The room temperature flexural strength was 447 MPa, with strength decreasing to 196 MPa at 1800 degrees C, and then increasing to 360 MPa at 2300 degrees C. The strength up to 1800 degrees 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 degrees C was controlled by flaws in the range consistent with sizes of the maximum ZrB2 grain size and the largest pores. Fracture toughness was 2.3 MPa center dot m(1/2) at room temperature, increasing to 3.1 MPa center dot m(1/2) at 2200 degrees C. The use of higher purity starting materials improved the mechanical behavior in the ultra-high temperature regime compared to previous studies.

Automated summary

A nominally phase pure ZrB2 ceramic was tested for its mechanical properties at ultra-high temperatures. The material showed high flexural strength and fracture toughness, with different controlling factors below and above 1800 degrees Celsius. The use of higher purity starting materials improved the mechanical behavior compared to previous studies.