| 摘要 |
The reliability of silicon nitride bodies for use in bearings can be greatly improved by dealing with microstructural defects which give rise to brightly shining reflections when the metallographically prepared surfaces of the composites are examined microscopically in low-angle impinging light, dark fieldreflected light or reflected polarized light which is viewed through an analyser having crossed polarization. The population of such defects can be dealt with by moderately increasing the normal quantity of intergranular phase and grinding for a longer time than normal prior to sintering. Grading the powder by size before compressing also improves the use properties of the body. The number of fatigue cycles which are required to produce faults in ten per cent of the silicon nitride surfaces tested at 6.9 GPa contact stress in the accelerated bearing fault ASTM test STP 771 (L10 parameter) for sintered bodies produced in accordance with the invention is increased by about one order of size above the values which are obtained with the best previously known type of silicon nitride body for use for bearings. |
