Abstract:
Titanium diboride has been investigated as a potential candidate for aerospace
structures, cutting tools, surface coatings of first-wall components and diffusion barriers
in integrated circuit metallization. Titanium diboride is a very stable hard refractory
compound but its brittleness is the main drawback. It was possible to lessen the TiB2
brittleness by producing TiB2/X coating designs by the multi-target RF magnetron
sputtering process. X is the metal layer (Al, Ti, NiCr, Mo) in the composite system.
The influence of the composition wavelength and volume fraction of ceramic
has been studied over a range of sputtering conditions. The most suitable multilayer
coating design (TiB2/NiCr) on steel substrate, for maximum hardness (18.81GPa) and
elastic modulus (304.6GPa) was found to be with a composition wavelength of 50nm
and volume fraction of ceramic of 75%. The greatest improvement of the elastic modulus
measured by nanoindentation was found to be for a TiB2/Al two-layer coating design
either on steel or on aluminium substrate, giving 36.2% and 40% improvement above the
rule of mixtures respectively, when compared with TiB2 coatings deposited under the
same sputtering conditions.
Several pieces of three-point bent apparatus were designed for measuring the inplane elastic modulus of the coatings. The three-point bent test by nanoindenter shows
promise as a method for measuring the in-plane elastic modulus on uncoated beams.
A comparison between traditional and non-traditional methods of measuring
mechanical properties of the coatings was performed in this study. The nanoindentation
technique was found to be an appropriate method to measure the mechanical properties
of multilayer coating designs.
