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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.

The paper examines how mechanical activation influences the in-situ phase formation of aluminosilicates in the BN-Al 2 O 3 -SiO 2 -Si 3 N 4 system. The major factor that influences the activation of the charge is the duration of high-energy machining. Results from infrared spectroscopy and data on the particle size and specific surface of the charge show that short-term (10-20 min) attritor grinding is sufficient to obtain a mixture and composite of high quality.