Monolayers (ML) of octadecylphosphonic acid (C18PA) were assembled on the native oxide surface of AISI H-11 tool steel. The transformation of P‑OH groups into P-O-M bonds was identified by X-ray photoelectron spectroscopy and anchors the alkyl chain to the tool steel. Tribological compression-torsion-wear-test (CTWT) of a steel surface covered with a C18PA-ML revealed reduced torque and hence reduced friction against aluminum compared to an uncoated steel reference. Contact-pressures of ≥ 75 MPa applied during CTWT underline the potential of this functionalization concept for industrial forming applications without liquid lubricants.

One core competency deals with the investigation of cutting tools and their cutting performance regarding substrates, geometries and coatings. Those kind of investigations can be realized in two different ways - basic-oriented research projects and application-oriented research projects. Looking back at years of investigations as well as close cooperations with tool suppliers and end-users, application-oriented research project types lead to fast, reliable and transferable results to optimize existing cutting processes and technologies. Basic-oriented research projects mostly do not consider the special circumstances that occur at the end-users production center. Those circumstances might be:

• component specific geometries

• stability level of machine, clamping setup and workpiece itself

• specialties in programming and strategy dimensioning

• end-user specific tooling solutions

To face these issues and to make the project results transferable, most of the investigations of the research group are application-oriented projects. To consider those factors for each specific project, an investigation method is being created, including project specific components, test strategies and measuring algorithms in an analytic procedure.

One example is the test of indexable insert cutters with different variants of PVD and CVD coatings for roughing of turbine blades out of stainless steel. Those variants differ in composition, thickness and structure of the coatings. Additional modification factors are micro geometrical changes and varieties of substrates. To fulfill the requirements of application-oriented research projects, the investigations are being performed as followed:

• design of a special turbine blade for roughing investigations

• use of turbine blade machining center and clamping setup

• application of turbine blade specific roughing cycles and NC-programs

• utilization of tooling solutions that are already being favored by the end-user

Differences of the various PVD and CVD coating variants are obvious. Tool life time can be increased drastically choosing the correct combination of substrate (toughness), micro geometry and coating. Future development tendencies for roughing of stainless steel can be concluded reliably to improve the performance of future coatings and tooling solutions. In addition these reliable results are easy to transfer to the end-users application.

[1] G. Greczynski, J. Lu, M. Johansson, J. Jensen, I. Petrov, J.E. Greene, and L. Hultman, Vacuum 86 (2012) 1036

[2] G. Greczynski, J. Lu, M. Johansson, J. Jensen, I. Petrov, J.E. Greene, and L. Hultman, Surf. Coat. Technol. 206 (2012) 4202

TiAl(O)N and CrAl(O)N coatings as deposited by means of High Power Pulsed Magnetron Sputtering (HPPMS) have shown excellent properties as wear resistant and anti-adhesive coatings on steel tools for polymer processing applications such as injection molding and extrusion. Although the coating technology is well advanced, the functional properties of such coatings, governed by the surface and interface chemistry, are not yet well understood. The coatings are typically deposited at relatively high temperature in chambers with “medium” vacuum, with the subsequent participation of background oxygen and water in the plasma process. The reactivity of the just deposited films and the subsequent exposure to the background and then to ambient atmospheres is likely to lead to a surface oxidation process, which will influence the functional properties of the coating [1].

We have developed an experimental approach that enables to investigate in-situ the changes in interface chemistry under different oxidation conditions and the corresponding change of functional properties such as passivation and adhesion. The changes in the surface chemistry were induced by oxygen chemisorption under high vacuum conditions at different pressures, plasma oxidation, as well as the oxide formation at ambient pressure, and they were investigated by means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and low energy ion scattering (ISS) both ex-situ and in-situ.

XPS, UPS and ISS data were combined with electrochemical data to correlate the structure with the electronic and corrosive properties of the surface near region. Moreover, in cooperation with the theoretical group of Jochen Schneider at the RWTH Aachen, we aim at the atomistic understanding of surface structure and surface properties as well as adhesive properties. E.g. the temporal evolution of the surface chemistry of TiAlN upon O₂ exposure at 300 K was probed by time resolved X-ray photoelectron spectroscopy (XPS) and the results were supported by ab initio molecular dynamics simulation [2]. Both the experimental and theoretical data imply that titanium determines the kinetics of the oxidation. Dissociative adsorption of oxygen is followed by the formation of Ti-O-Ti bridges. The thereby formed Ti(III)-oxide inhibits further oxidation of the underlying TiAlN at low oxygen partial pressures.

[1] Kunze et al. Surf. Interface Anal. 45 (2013) 1884–1892

[2] Kunze et al, Appl. Surf. Sci. 290 (2014) 504– 508