Visualization of knoop indentation damage of silicon nitride by plasma etching

A visualizing technique for indentation damage of ceramics was developed. P lasma etching was used to enhance the view of cracks and the subsurface mic rocracking crush zone following Knoop indentation of hot pressed Si3N4. The microcracking zone was readily identified from the surface view of the ind ented surface as a grain-falling-off region (GFOR), defined as a region in which grains were removed by preferential etching using CF4 gas, followed b y ultrasonic cleaning. A fissure-like opening corresponding to the indentat ion cracks was also observed. It is inferred that the formation of the GFOR region and the fissure-like opening were caused by the etching/cleaning tr eatment. Meanwhile, the etching on a section which included diagonals of th e impression provided a section view of the microcracking zone.