Materials for thin-film wear sensors

This paper addresses the problems of material selection and fabrication of sensors for steel bearings and reports test results for sliding ring and block tests (ASTM-G77). A thin-film wear sensor has been constructed to monitor the wear of a bearing surface while in contact with a shaft or flat counterface. The sensor consists of electrically conductive films separated from the bearing with insulating films. It monitors the regression of the surface due to wear in fractions of a micrometer over a small area. The effect of the materials and fabrication on the properties of the sensor are presented as they affect the electrical response and wear characteristics. The most critical properties of the insulating film are adhesion, low conductivity, strength, and hardness. Sputtered films of aluminum oxide, tantalum oxide, and borosilicate glass on 304 stainless steel substrates were evaluated. It was found that conductive films of copper and aluminum smeared excessively, but that films of platinum and tantalum could be used successfully for thin-him wear sensors as well as insulators of alumina and tantalum oxide.