MECHANICAL PROPERTIES OF POLYTYPOIDALLY JOINED Si_3N_4-Al_2O_3

摘要

Crack-free joining of alumina and silicon nitride has been achieved by a unique approach introduc- ing sialon polytypoids as a functionally graded materials(FGM)bonding layer. The polytypoid compositions are identified in the phase diagram of the Si_3N_4-Al_2O_3 system. The thermal stresses of this FGM junction were analyzed using a finite element analysis program taking into account both coefficient of thermal expansion and modulus variations. From this analysis, the result showed a dramatic decrease in radial, axial and hoop stresses as the FGM changes from three layers to 20 graded layres.