Abstract:
Titanium diboride (TiB2) has been investigated as a potential candidate for
several industrial applications, such as: cutting tools, electric devices, wear
parts and many more fields of application. The main drawback of TiB2 is its
brittle nature, which has limited its range of applications.
Diamond-like Carbon (DLC) has been used in industrial applications, mainly for
wear resistant parts. However, the application of DLC films has been limited by
the level of internal stress accumulated during deposition.
This thesis investigates the deposition of TiB2/DLC multilayer wear resistant
coatings to overcome these limitations. The thesis focuses on the tribological
effects caused by different deposition techniques on TiB2 ceramic used by the
coatings industry today, in order to overcome the brittle nature of TiB2 and the
lack of adhesion of DLC films.
The multilayer coatings consisted of 25 bi-layers of TiB2/DLC. These TiB2/DLC
coatings were fabricated, maintaining a constant composition wavelength (sum
of two layers λ =200 nm) for an array of ceramic fractions ranging from 25% to
95% by volume using as substrates, tool steel AISI 1095 and powder metallurgy
aluminium alloys, type 2618. The effect of the DLC content on the structure and
performance (hardness, adhesion and wear) of the films was investigated. The
bi-layer thickness influences the failure patterns observed in the scratch testing.
These observations have been used to optimise the multilayered coating
structure.
Multilayer coatings have been manufactured to increase surface hardness and
wear resistance as applied to a commercial powder metallurgy Al alloys (Al
2618) used in the automotive industry. Optimum coatings have found hardness
values of 27.8 GPa, with a critical load of 20 N and a friction coefficient of 0.47.
As a result of wear tests the multilayer with 10% of DLC was found to be best
compromise between high hardness (23.8 GPa), good adhesion (critical load
higher than 20 N), low friction and low wear rate.
