Surface topography effect on galling resistance of coated and uncoated tool steel

Tribological evaluation of the tool steel, focused on determining coefficient of friction and critical load for galling initiation against austenitic stainless steel as a function of surface topography was carried out in a load-scanning test rig. Surfaces investigated included turned, ground, polished, shot penned and laser surface textured cold work tool steel. Additionally, effect of surface roughness and post-polishing on galling resistance of TiN and DLC coated surfaces was investigated. Results of this investigation show that by removing sharp peaks polishing of the bearing surface gives plateau-like topography and improves galling properties of forming tool steel. This becomes even more important when using hard ceramic coatings (i.e. TiN). When superbly polished contact surfaces can give similar galling resistance as otherwise obtained through contact lubrication. However, application of low friction coatings or introduction of micro-dimples with proper density and contact lubrication will result in superior galling resistance of the surface. (C) 2011 Elsevier By. All rights reserved.