2nd Internat. Symp. on SiAlONs and Non-Oxides, Mie, Japan, 02.12-05.12.2007

Surface Structuring of a/b-SiAlON Ceramics by Plasma-Etching

M. Riva*^a, S. Holzer ^a, R. Oberacker ^a, M.J. Hoffmann ^a, C. Ziebert ^b

^a Institute for Ceramics in Mechanical Engineering, University of Karlsruhe

76131 Karlsruhe, Germany

^b Institute for Materials Research I, Forschungszentrum Karlsruhe,

Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen

76021, Karlsruhe, Germany

E-mail: marco.riva@ikm.uni-karlsruhe.de

The plasma-etching technique with a reactive gas is a common practice to investigate the microstructure of Si₃N₄. In this case the b-grains show a greater etching rate than the grain boundary glassy phase, so that they are preferentially dissolved and the microstructure is revealed.

In this study it was tried to transfer this effect to sialon ceramics but with the aim to create a height-relief in the surface with the function of micro lubrication pockets for the application in lubricated gliding systems.

During this study the effects of plasma etching on sialon ceramics by CF₄/O₂ were investigated. It was shown that b-grains exhibit a higher etching rate than the grain boundary glassy phase or the a-grains, generating pockets in a range of few µm. According to this, the bearing ratio of such a surface can be adjusted by the relation of quantity of a/b-sialon and the depth of the lubrication pockets by etching parameters like in this case the dwell time.

Therefore sialon samples with different a/b-ratio were produced and subsequently etched under different conditions.

The so created surfaces were characterized both by sScanning electron microscopy (SEM) and by atomic force microscopy AFM (AFM) analysisin contact mode. These complementary techniques also enabled the determination of the bearing ratio. Certain selected compositions and etching conditions have been applied on samples which were investigated in tribological measurements in self-mated pair.