Unlubricated sliding wear of ceramic materials

Abstract

The potential use of thermal insulating ceramic coatings on the cylinder walls of diesel engines at elevated temperatures requires that an understanding of the operative friction and wear mechanisms be gained. An investigation was carried out to determine the unlubricated sliding wear behavior of a thermal insulating oxide coating in combination with a number of carbide, boride, and mixed oxide coatings at room and elevated temperatures to 730 °C. The coatings were applied up to several hundred micrometers thick by plasma spray and chemical vapor deposition (CVD) processes on flat washers and discs and tested at contact pressures up to 6.9 MPa to steady state wear conditions in a rotational reversing motion. Wear rates, coefficients of friction and wear surface compositions and morphologies were determined. It was found that the binder metal in sprayed metalcarbide composites had a dominant influence on the wear, more so than the composition of the carbide. Different wear surface morphologies and attendant wear rates occurred at each of the test temperatures. The shape of the deposited grains in the CVD coatings had a major effect on the wear rates; rounded grains being better than angular grains of the same material. A film formed on the TiB 2-mixed oxide wear pairs that could have a significant effect on their wear behavior.