Hexagonal boron nitride was pressed and sintered at 2000 degrees C with CaB2O4 as an additive to promote its crystallization, which was used as an abradable sealing coating for aircraft turbo engines. Microstructures, phase compositions and tribological properties of the sintered hBN were tested, and the results show that CaB2O4 can effectively promote crystal growth of hBN at 2000 degrees C for 5 h in N-2 ambience. The friction coefficients of the sintered hBN under atmosphere ambience increase as the temperature increasing from room temperature to 400 degrees C, and then decrease with further increasing of temperature up to 800 degrees C. Under water vapor ambience, friction coefficients of the sintered hBN are much lower than those under atmosphere ambience, which are attributed to a lamella-slip of hBN and the solid lubrication effect of H3BO3. (C) 2011 Elsevier B.V. All rights reserved.