Composition, microstructure and mechanical properties of boron containing multilayer coatings for hot forming tools H. Paschke a, ⁎, M. Stueber b , C. Ziebert b , M. Bistron c , P. Mayrhofer d a Fraunhofer Institute for Surface Engineering and Thin Films IST, Eberhardstraße 12, D-44145 Dortmund, Germany b Karlsruhe Institute of Technology, Institute for Materials Research I, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany c Institute of Metal Forming and Metal-Forming Machines IFUM, Dep. of Massive Forming, Leibniz Universitaet Hannover, An der Universitaet 2, D-30823 Garbsen, Germany d Department of Physical Metallurgy and Materials Testing at Montanuniversitaet Leoben, Franz-Josef-Straße 18, A-8700 Leoben, Austria abstract article info Available online 12 May 2011 Keywords: Nanostructures PECVD Boron based coatings Wear/abrasion-resistant coatings Multilayer coatings The tribological conditions of hot forming processes are much different from those at room temperature. Thus classical wear-resistant coating like CrN, CrAlN, TiAlN in most cases are not sufficient for hot forming tools in industrial applications. Additionally the use of lubricants is limited, thermal shock conditions and the increase of sticking work piece material are leading to severe wear. This paper presents examples for ternary boron based Ti–B–N gradient coatings in specific multilayer designs obtained through plasma enhanced chemical vapor deposition. After a thorough characterization of the chemical composition by Auger electron spectroscopy, the microstructure by X-ray diffraction and the mechanical properties by microindentation and small-angle cross section nanoindentation, the coatings were applied onto hot forming tools made from DIN 1.2367 tool steel. The coated tools were tested in hot forging of AISI 1043 raw parts in an automatic press and have been compared in terms of adhesion and wear resistance. In this study an optimum design has been found which significantly reduces sticking of work piece material and wear. This allows an efficient production without interruptions for a reworking of the tools and enables to increase the process reliability paired with a longer tool life. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In hot forming environments, very specific wear conditions cause tool failure. At elevated process temperatures, high forces are supporting the adhesion of work piece material on the tool surfaces. The shearing of this sticking material in following forging strokes is causing adhesive wear as a result. Other wear mechanisms that are occurring are caused by oxidation of the work piece surface which creates hard particles like scale and thus extensive abrasive wear. Additionally thermal shock conditions are present because during material processing the thermal loading from the heated material will be followed by cooling cycles. As a consequence these conditions are leading to reduced tool life. Tools have to be reconditioned or changed often after forming of less than 100 or 1000 parts. The resulting costs for tools, necessary production interrupts and off-time for shutting down the production machinery will lower the efficiency of the production procedures. Modern tool surfaces have to accomplish various functions in the field of hot forming. To meet these partly contradictory requirements very complex surface properties are essential which is impossible to achieve with simple mono layer coatings. Standard solutions like nitriding, coatings with CrN or galvanic hard chromium are existing coating solutions, but they are very quickly reaching their limits. Possible coating solutions with a high potential for hot forming operations can be found within the boron containing systems. Several studies on nano-structured boron containing PECVD coatings show this [1–3]. In recent years, the plasma coating technology has devel- oped more and more complex coating systems using new materials and new coating designs [4,5]. To allow the use of interesting but difficult material candidates like TiB 2 with high hardness, but high internal stresses, coatings with gradients in material composition have been succesfully applied. Present-day coatings are nearly always deposited in multilayered structures where the properties of the single layer materials are combined and mechanical enhancement is a result of these structures where crack energy is dissipated. A further possibility for material improvements for thermal applications is the formation of structures in the nanoscale [6,7]. Due to their high hardness and good resistance against high tem- perature oxidation and corrosion boron nitride based transition metal coatings have attracted attention in recent years. The deposition is possible with different coating techniques while the presented wear protection films solely are processed with PECVD techniques. Ti–B–N Surface & Coatings Technology 205 (2011) S24–S28 ⁎ Corresponding author. Tel.: + 49 231 844 5453; fax: + 49 231 844 5452. E-mail address: hanno.paschke@ist.fraunhofer.de (H. Paschke). 0257-8972/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2011.04.097 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat