Effects of Laser Surface Texturing on the Microstructure and Frictional Characteristics of Zirconia Surfaces Under Liquid and Solid Lubrication

Abstract

The production of dimple patterns in surfaces by laser surface texturing (LST) has received considerable interest. The current research characterized the effects of LST on the near-surface microstructures in transformation-toughened zirconia (TTZ) and investigated how dimpling can affect reciprocating frictional behavior under both liquid and solid lubrication. Microstructural characterization included scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning acoustic microscopy (SAcM), and nanoindentation testing. Fine-scale micro-cracks were observed in both the rims and bottoms of dimple craters. Most of the laser-affected zone is composed of very fine grains with diameters 125∼150 nm, but no grain structure was observed nearest the rim edges. The distribution of residual stresses around the dimples, induced by LST, was revealed by SAcM. Nanoindentation tests of TTZ indicated no significant differences in hardness or elastic modulus between the material near the dimples and in the bulk. Counterface materials in the flat-on-flat reciprocating sliding tests included silicon nitride and a galling-resistant stainless steel. Friction tests were conducted under both liquid (mineral oil) and solid (fine graphite powder) lubrication. Dimpling did not show measurable improvement on frictional behavior under the applied test conditions, although they were supposed to function as lubricant reservoirs and debris traps.