MORPHOLOGICAL EFFECT OF 2ND-PHASE ON THE THERMAL-CONDUCTIVITY OF ALN CERAMICS

The effect of the morphology of second phases in sintered microstructu re on the thermal conductivity of AIN ceramics was investigated. When an Y2O3-doped AlN specimen was cooled down slowly at a rate of 3 degre es C/min after sintering at 1850 degrees or 1900 degrees C, the second phases were concentrated in the corners of the AlN grains by an incre ase of dihedral angle during cooling, On the other hand, the fast-cool ed specimen at a rate of 60 degrees C/min showed a different structure of the second phases interconnected through the triple-grain junction s, The specimen with isolated second-phase morphology showed a higher thermal conductivity than those with interconnected second-phase morph ology, The measured thermal conductivity of the specimens with differe nt morphologies of the second phases agreed well with the calculated o ne derived from modeled microstructures. From the comparison of the me asured and calculated thermal conductivity, it was shown that the ther mal conductivity of the specimen with interconnected second-phase morp hology decreased steeply with an increase of the amount of the second phases, assuming the content of lattice oxygen to be constant, However , the thermal conductivity of the specimen with isolated second-phase morphology was rather insensitive to an increase of the amount of the second phases.