A PACVD duplex coating for hot-forging applications

The tribological loading of forging tools is caused by the relative motion between the plastically deformed work piece and the die. In comparison to many other forming processes, hot forging has an especially disadvantageous tribological system, combining thermal, mechanical and chemical loadings. The advantages of hard coatings, which are well known for cutting tools, are to a much lesser extent explored for casting, extrusion, moulding and forging tools. Increasing the lifetime of these tools is an important task in surface engineering because of the complex loading conditions and the often complicated tool geometry, with the plasma-assisted chemical vapour deposition (PACVD) technique being well suited to the depositing of hard coatings onto large dies and moulds. The aim of this paper is to present and discuss possible improvements to industrial applications (i.e., the hot forging of automotive parts) obtained by the duplex PACVD coating of forging dies. The experimental results indicate that the deposition of a proper duplex PACVD coating and the use of a proper substrate treatment lead to improved tribological properties and a longer lifetime for the hot-forging die. (c) 2008 Elsevier B.V. All rights reserved.