Wear protecting layers in
cutting processes
S. Ulrich, C. Ziebert
Forschungszentrum Karlsruhe, Institut
für Materialforschung I, Hermann-von-Helmholtz-Platz 1, D-76344
Eggenstein-Leopoldshafen, Germany
In order to increase the productivity since the
1960-ties coating materials are used in the machining industry, that are
deposited by PVD (physical vapour deposition) and CVD processes (chemical
vapour deposition). Despite this long period only a few well-established
coatings such as TiN, TiC, TiCN, TiAlN, TiAlCN, CrN, CrAlN, TiAlCrN, Al2O3,
amorphous carbon (a-C) and diamond as well as their combinations in classical
multilayers cover a broad application spectrum in a quite general fashion. The
friction coefficient of these coatings against steel is higher than 0.5 apart
for the a-C and diamond coatings and the coating development was mainly focused
on a single functionality, namely the enhancement of the wear resistance. However,
the globalisation of the markets brings the need for new materials to increase
productivity, cutting speed and tool lifetime, to improve the surface quality
of the machined components and to develop dry cutting processes to omit environmental
pollution by lubricants. Therefore new multifunctional nanolaminated coatings with tailored mechanical, tribological and chemical features
should be developed, realized and optimized to dry cutting applications. Here,
the challenge is to understand and control the mechanisms of wear, corrosion,
phase changes and crack formation in the coatings and their interfaces in order
to extend the lifetime of the cutting tools and to decrease pollution and
increase productivity. This requires an interdisciplinary approach, which
combines latest developments on multifunctional nanolaminated coatings with
high performance analytics for determining composition, microstructure,
residual stresses, nanoscale properties, and coating failure as well as with
multiscale materials modelling. Therefore the most important goals in this
field of R&D are i) the optimisation of new multifunctional nanolaminated
coatings and their interfaces by an improved understanding of the interaction
mechanisms between the layers in the interface regions and the influence of
constitution and thermal stability of these interfaces on the structure,
properties and machining behaviour of a coated tool in cutting applications.
ii) the development of new nanoscale characterisation methods for residual
stresses and defects with high lateral and depth resolution with the
possibility of an in-situ measurement of this features during the cutting
process and iii) a multiscale model that is able to cover all length scales
from atomistic over mesoscopic to macroscopic scale and can describe both the
coating deposition and properties and the local and global wear and defect
formation during the cutting process.