Surface modification to improve friction and galling properties of forming tools

The aim of the present work was to investigate and compare different surface modification techniques in terms of galling properties when applied on forming tools. The surface modification techniques included were different grades of polishing, plasma nitriding and DLC coating, all applied to cold work tool steel, respectively. Tribological evaluation against austenitic stainless steel was carried out in a load-scanning test rig. A special test configuration makes it possible to gradually increase the normal load during testing, with the load being in the range between 100 and 1300 N (1-3.5 GPa). It is concluded that the galling tendency can be greatly reduced by proper polishing of the tool surface. However, selection of a carbon-based multilayer WC/C coating leads to substantially reduced probability of work material transfer even at a relatively high surface roughness, and also under starved lubrication. If polished after treatment, a plasma nitrided surface will provide improved friction and wear properties of the tool steel and to some extend also reduce the galling tendency in sliding against austenitic stainless steel. A combination of nitriding, surface polishing and DLC coating is suggested as the optimum surface treatment of tools aimed at forming austenitic stainless steel. (c) 2006 Elsevier B.V. All rights reserved.