Title: On adhesion of work material in metal forming

Authors: Magnus Hanson, Sture Hogmark, Ernesto Coronel, Daniel H.E. Persson

Addresses: Uppsala University, Box 534, SE-751 21 Uppsala, Sweden. ' Uppsala University, Box 534, SE-751 21 Uppsala, Sweden. ' Uppsala University, Box 534, SE-751 21 Uppsala, Sweden. ' OC Oerlikon Balzers AG, Coating Services, Iramali 18, LI-9496 Balzers, Liechtenstein

Abstract: 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.

Keywords: metal forming; adhesion; galling; stainless steel; TiN coating; transmission electron microscopy; TEM; focused ion beam; FIB; dry forming; metal transfer; interfacial oxide; austenitic steel.

DOI: 10.1504/IJMMP.2008.018744

International Journal of Microstructure and Materials Properties, 2008 Vol.3 No.2/3, pp.401 - 412

Available online: 16 Jun 2008 *

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