Mechanical Properties and Thermal Shock Resistance of SrAl2Si2O8

Hexagonal boron nitride (h-BN) h-BN) ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles, owing to their superior thermal stability and excellent dielectric properties. However, their densification during sintering still poses challenges for researchers, and their mechanical properties are rather unsatisfactory. In this study, SrAl2Si2O8 2 Si 2 O 8 (SAS), with low melting point and high strength, was introduced into the h-BN ceramics to facilitate the sintering and reinforce the strength and toughness. Then, BN-SAS ceramic composites were fabricated via hot press sintering using h-BN, SrCO3 , 3 , Al2O3 , 2 O 3 , and SiO2 2 as raw materials, and effects of sintering pressure on their microstructure, mechanical property, and thermal property were investigated. The thermal shock resistance of BN-SAS ceramic composites was evaluated. Results show that phases of as-prepared BN-SAS ceramic composites are h-BN and h-SrAl 2 Si 2 O 8 . With the increase of sintering pressure, the composites' densities increase, and the mechanical properties shew a rising trend followed by a slight decline. At a sintering pressure of 20 MPa, their bending strength and fracture toughness are (138 +/- 4) MPa and (1.84 +/- 0.05) MPa<middle dot>m1/2 , 1/2 , respectively. Composites sintered at 10 MPa exhibit a low coefficient of thermal expansion, with an average of 2.96x10-6 -6 K -1 in the temperature range from 200 to 1200 degrees C. The BN-SAS ceramic composites prepared at 20 MPa display higher thermal conductivity from 12.42 to 28.42 W<middle dot>m-1<middle dot>K-1 -1 <middle dot>K -1 within the temperature range from room temperature to 1000 degrees C. Notably, BN-SAS composites exhibit remarkable thermal shock resistance, with residual bending strength peaking and subsequently declining sharply under a thermal shock temperature difference ranging from 600 to 1400 degrees C. The maximum residual bending strength is recorded at a temperature difference of 800 degrees C, with a residual strength retention rate of 101%. As the thermal shock temperature difference increase, the degree of oxidation on the ceramic surface and cracks due to thermal stress are also increased gradually.