A novel BN–MAS system composite ceramics with greatly improved mechanical properties prepared by low temperature hot-pressing

Effect of magnesium aluminum silicate glass on the thermal shock resistance of BN matrix composite ceramics

“…The results of dilatometric measurements for BN‐MAS composite ceramics are displayed in Figure . The average CTEs rise from 4.03×10 −6 K −1 (S1) to 6.89×10 −6 K −1 (S5) with increasing MAS loading, likely a result of enhanced formation of mullite and the degree of crystallization of h ‐BN . As seen in Figure A, CTEs of composites increase with the rise of temperature, which can be attributed to the increasing atomic spacing at elevated temperatures.…”

“…However, the use of single‐phase h ‐BN materials for high‐temperature structural applications is rather limited because of poor sinterability and weak oxidation resistance as well as relatively poor lower mechanical properties . Therefore, the densification and mechanical properties of h ‐BN combined with second phase have been studied in the past decades …”

“…5,6 Therefore, the densification and mechanical properties of h-BN combined with second phase have been studied in the past decades. 7,8 Although enhanced mechanical performance of h-BNbased ceramics is a crucial step forward, to make it an attractive choice under extreme environmental conditions, several properties are still need to be improved. 1,9,10 As a thermal protection component of high-speed vehicles, they served in an oxidizing environment of high velocity dissociated air, which are susceptible to catastrophic failure under severe thermal stress.…”

An Overview of Ceramic Matrix Composites

“…As such, most of h-BN matrix composite ceramics are manufactured by hot pressing sintering method with various additives in order to improve their mechanical properties. During the sintering process, experimental parameters including temperature, pressure and soaking time have obviously effect on the performances of sintered samples [7][8][9]. A novel h-BN-MAS (magnesium aluminium silicate) composite ceramics with greatly improved mechanical properties prepared by hot-press sintering under relatively low temperature.…”

“…That is, within each layer, boron and nitrogen atoms are bound together by strong sp 2 covalent bonds, and the adjacent layers are integrated by weak vander waals forces [5][6][7][8]. This special crystal structure provides h-BN a series unique combination of properties, including low dielectric coefficient, low loss tangent, extremely high sublimation temperature of about 3000 o C(non-oxidizing atmosphere), excellent thermal shock resistance, and desirable machinability [9].However, there exist some problems that limit the application of h-BN material, such as low strength and poor sintering properties. As the strong covalence of B-N bond has a rather low self-diffusion coefficient, it is difficult to obtain dense materials even if they are sintered under high temperature (>2000 o C) or assisted by pressure.…”