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L. Lobmaier:
"Intermetallic target materials in PVD based deposition techniques: A case study for Ti-Al-N coatings";
Supervisor: H. Riedl, L. Zauner; Institut für Werkstoffwissenschaft und Werkstofftechnologie, 2020; final examination: 2020-03-27.

Hard protective coatings are an essential surface modi cation for state of the art cutting and
milling inserts, enabling higher performance with respect to cutting speed, thermal stability,
or durability. Within this context, titanium aluminium nitride (TiAlN) has evolved to an
application proven material system, o ering high hardness, combined with excellent wear-, and
oxidation resistance. As the performance of the coatings not only relies on the physical vapor
deposition (PVD) technology, but also on the quality of the source material { setting highest
requirements with regard to purity and density { targets are a cost-intensive part of the thin
lm synthesis process. Industrially sized Ti-Al targets with an aluminium content > 20 at.%
are typically produced via forging, as a uniform elemental distribution and a ne-grained
microstructure are of signi cance to achieve excellent target performance. Nevertheless,
the once elaborately manufactured PVD-targets become inoperable after 30 to 70 % of
the material has been eroded, leaving most of the material unused. Therefore, an attempt
has been made to recycle the remaining high-quality target materials, leading to a novel
intermetallic, multiphased TixAly target design.
Within this study, an in-depth comparison of recycled intermetallic TiAl (50/50 at.%)
targets (IM) and conventional powder metallurgically ones (PM) of identical composition
is presented from the aspect of di erent PVD techniques, and respective lm properties. A
nitrogen variation is conducted during direct current magnetron sputtering (DCMS), highpower
impulse magnetron sputtering (HiPIMS), as well as cathodic arc evaporation (CAE).
Structural analysis of the virgin IM target reveals the presence of several intermetallic phases
(e.g.,
-TiAl, 2-Ti3Al, or TiAl2), whereas a pure two-phased structure (i.e., hexagonal-Ti and
cubic-Al) is identi ed for the PM target. While no phase transition is observed on the target
surface after DCMS and HiPIMS, signi cant changes occur during CAE. For both targets
identical intermetallic as well as nitride-based phases { such as face centered cubic (fcc) TiAlN
{ have been recognized after arc evaporation. In addition, DCMS discharges of the two target
types obtained strongly varying poisoning behaviour. IM targets show a smooth and quasi
hysteresis-free transition from the metallic to the compound dominated mode, whereas an
abrupt poisoning is observed for the PM target accompanied by a pronounced hysteresis e ect
1
Abstract
{ transition zone from 0.22 to 0.34 Pa nitrogen partial pressure. Consequently, this unequal
poisoning behaviour is re
ected in the deposition rates and the required nitrogen partial
pressure during DCMS to stabilise fcc-structured Ti43Al57N. On the other hand, reactive
HiPIMS deposition from both target types, performed under signi cantly low nitrogen partial
pressure (0.08 to 0.12 Pa) allows for a steady transition from wurtzite to purely fcc-structured
coatings without revealing a distinct decrease in the deposition rate due to target poisoning.
During CAE the usage of the two di erent target type reveals only minor changes with
respect to structural evolution growth characteristics. Despite the absence of low-melting,
elemental aluminium within the IM target, top view analysis of the arc evaporated coatings
reveals the formation of more, yet smaller macroparticles compared to thin lms deposited
from PM targets. Indentation hardness and modulus of all synthesised fcc-phased Ti1􀀀xAlxN
are empirical superior with the highest hardness obtained during HiPIMS (H 35 GPa,
E 400 GPa), followed by CAE (H 33 GPa, E 460 GPa), as well as DCMS (H 31 GPa,
E 450 GPa). This study highlights the importance of a well-described target constitution,
based on either purely metallic but also intermetallic phases, leading to interesting e ects
with respect to target poisoning and phase stabilization. The utilization of IM TiAl targets
allows for depositions at high nitrogen partial pressures without pronounced target poisoning
and related process instabilities.

Project Head Helmut Riedl:
CDL-SEC