Hexagonal boron nitride (h-BN) composite ceramics were prepared by hot pressing with the addition of Y2O3 and AlN.The effects of different YaO3-AlN contents on microstructural evolution,mechanical properties and thermal diffusion coefficients of h-BN composite ceramics were investigated.The results indicate that Y2O3-AlN forms a liquid phase during the sintering process,achieving a good wettability with h-BN grains.In pure h-BN ceramic and h-BN composite ceramic with 40 wt％ Y2O3-AlN,the h-BN grains grow well when controlled through solid-phase and liquid-phase diffusion,respectively.With the increase in Y2O3-AlN content,mechanical properties and thermal diffusion coefficients of h-BN composite ceramics first decrease and then increase,and the properties of h-BN composite ceramic with 10 wt％ Y2O3-AlN are the inflection points.Such properties are highly related to the phase compositions,porosity and microstructure.