| The chemical modification of ceramics by boronization in a packed container was investigated in the systems Al-B-O and Si-N-B. The ternary phase diagrams of the Al-B-O system at 1500 K and of the Si-N-B system at 1600 K were calculated to provide guidelines for the pack treatment. Thermodynamic properties of the constituent phases were determined from published data, and when unknown, were obtained by comparing the experimental and the calculated phase diagrams of the binary systems Al-B and {dollar}rm Alsb2Osb3{dollar}-{dollar}rm Bsb2Osb3.{dollar}; The boronization of alumina and silicon nitride was performed in a graphite container and in an argon flow. The resulting products were in agreement with the calculated phase diagrams. The boronization of {dollar}rm Sisb3Nsb4{dollar} produced a h-BN film. The h-BN film decreased the friction coefficient of {dollar}rm Sisb3Nsb4{dollar} from 0.65 to 0.45, but showed rapid wear. The boronization of alumina led to the formation of a complex surface layer consisting of free boron, boron oxide and either {dollar}rm 9Alsb2Osb3cdot 2Bsb2Osb3{dollar} or {dollar}rm 2Alsb2Osb3cdot Bsb2Osb3,{dollar} depending on the processing conditions. During the sliding process, the {dollar}rm 2Alsb2Osb3cdot Bsb2Osb3{dollar} film was transformed to a glassy phase, which decreased the wear rate of the alumina disc by a factor of 10. The {dollar}rm 9Alsb2Osb3cdot 2Bsb2Osb3{dollar} film protected both the ball and the disc. For a 10 {dollar}mu{dollar}m-thick {dollar}rm 9Alsb2Osb3cdot 2Bsb2Osb3{dollar} film, the wear rate of the ball was negligible, and the wear rate of the disc was decreased by a factor of 3.5 for a sliding distance of 8000 meter under a load of 9.8 N. |
