Fracture behavior of a CVD crystalline Si3N4/amorphous Si3N4 composite.

摘要

The mechanical properties of a chemically vapor deposited (alpha)-Si(sub 3)N(sub 4)/amorphous Si(sub 3)N(sub 4) composite were examined at 25(degree)C and up to 1400(degree)C using a microhardness tester. The composite consists of an amorphous matrix containing elongated (alpha)-Si(sub 3)N(sub 4) particles (5--50 (mu)m in diameter) which in some cases are radially microcracked. The conditions for spontaneous microcracking due to thermal residual stress are derived for a cylinder embedded in a matrix. Heat treatment of the composite at 1200(degree)C results in a microstructure where the matrix consists of nanometer-sized particles separated by thin (50 (angstrom)) layer of carbon. The indentation fracture toughness of the heat treated material improves remarkably due to extended microcracking through the carbon layer.