Structure and high-temperature strength of composite materials based on boron nitride

Abstract

The structure and physicomechanical properties of composite materials based on boron nitride within which new phases (mullite and sialon) form during hot compaction are studied. It is established that the microstructure of composites is specified by their texture formation caused by the crystal morphology of boron nitride particles and it is almost independent of composite phase composition. It is shown that the main factor that affects strength is porosity. The dependence of strength on porosity is exponential in character. The strength of boron nitride − mullite and boron nitride − sialon composites is 110-140 MPa and at 20-1200°C it is almost unchanged.

Effect of mechanical activation on the in situ synthesis of aluminosilicates in the BN-Al2O3-SiO2-Si3N4 system

“…We earlier established that high-density samples of composites based on boron nitride and aluminosilicates (2.19-2.24 g/cm 3 dense) have high bending strength (120-140 MPa). The strength decreases with increasing porosity and is 30-50 MPa at a porosity of 18-23% [4].…”

“…Of practical interest are composites in which aluminosilicates are introduced to participate in controlled in situ phase formation and structurization. Our research shows that the use of SiO 2 , Al 2 O 3, and Si 3 N 4 as components of the charge for producing boron nitride-based composites promotes the synthesis of mullite and sialon in hot pressing and substantially decreases the temperature and pressure of the process [3,4].…”

Microstructure and mechanical properties of h-BN/Y2SiO5 composites

“…Incorporation of hard second phase, such as ZrO 2 , SiC or AlN, has been proven to be an effective way to improve the mechanical properties. In addition, the wear and corrosion resistance can also be improved [4][5][6][7][8][9].…”

“…Recently, singlephase bulk yttrium silicates have been successfully fabricated and characterized by Sun et al [12,13]. Interestingly, they show moderate hardness (5)(6) and are also belong to the family of "machinable ceramics". Owing to their low thermal conductivity and excellent corrosion resistance, they were also regarded as promising candidates for oxidation-resistance, thermal, and/or environmental barrier coatings [14][15][16].…”

Reaction hot-pressing and property-composition relationships of modified sialon – boron nitride hetero-modulus ceramics

“…insulation in electric propulsion thrusters) [6] to metallurgy and machinery (diaphragms for continuous casting, highly loaded brakeshoes, etc) [12]. The high performance and excellent mechanical, thermal and electrical properties of Si 3 N 4 -and sialon-containing HMC were confirmed by various researchers [13][14][15][16][17][18][19][20]. 4 To whom any correspondence should be addressed.…”