The transfer of work material to the tool surface limits the tool life in many forming operations. Using a dedicated load-scanning test equipment with crossed-cylinder geometry, dry forming of austenitic stainless steel was simulated by provoking adhesion to the TiN-coated tool specimen. High-resolution electron microscopy combined with analytical techniques was used to examine the interface between tool and work material. The decisive mechanism for adhesion and transfer of steel to the TiN surface is suggested. The oxide layer on the steel surface, especially the Fe-oxide, initiates the metal transfer. The interfacial oxide acts as a glue between stainless steel and TiN and increases the adhesive forces. Obviously, the adhesion and internal strength of the oxide layer is far stronger than anticipated. It may even be stronger than the bonding to the austenitic steel itself. A consequence of these findings is that the development of galling resistance-forming tool materials and coatings for austenitic stainless steels should not only aim to improve the bulk tool material, but also to reduce the adhesion strength between the tool surface and the oxide layer on the work material.

Materials from the Stellite family of Co-based alloys are commonly used as low friction, galling resistant materials in high load dry sliding contact applications.In the present investigation, the surface region of a Co-based material (Stellite 21) exposed to self-mated high load dry sliding at room temperature has been analysed in detail.During sliding, an approximately 30 nm thick Co-enriched tribofilm is created. It exhibits low friction properties and a high galling resistance. The transformation from an face-centred-cubic structure to easily sheared hexagonal-closed-packed basal planes in the tribofilm combined with the high load carrying capacity of the underlying deformation hardened zone is suggested to explain the excellent low friction properties and galling resistance of this material. (c) 2005 Elsevier B.V. All rights reserved.

The Stellite family of Co-based alloys is known to offer superior performance in many demanding sliding contact applications. However, alternative materials with corresponding properties are searched for, e.g. due to the fact that wear and corrosion products of Co run the risk of activation in nuclear plant applications. Furthermore, due to the high price of Co, a competitive, less expensive alloy would be very welcome for use in many applications.The present investigation examines the frictional behaviour and galling resistance of the laser processed Fe-based alloy Norem 02 at temperatures ranging from room temperature (RT) to 250 degreesC. Friction and galling testing was performed by sliding two crossed test rods in a load-scanning test rig. The results are compared with those previously attained from laser processed Stellite 21, one of the best low friction, galling resistant Co-based alloys.At RT Norem 02 exhibited excellent sliding performance, comparable to that of Stellite 2 1, showing a low and stable friction coefficient at a level of 0.25, and no tendencies to gall. However, at temperatures of 150 degreesC or above, the friction coefficient raised to a level of 0.5-0.7 and massive galling was observed for Norem 02. Stellite 21, however, maintained its excellent friction performance at those temperatures. Consequently, laser processed Norem 02 might not be suitable as a candidate material to replace Stellite in valves and seals in the primary circuit of nuclear power plants, which usually operate at temperatures considerably higher than RT. (C) 2003 Elsevier Science B.V. All rights reserved.