2.2. Coating procedures
The tensile and fatigue specimens were sent to Guhring Australia Pty Ltd for commercial grade PVD coatings. Two relatively
new coatings that are commercially available were used; TiAlN coatings and multilayered TiAlN/CrN coatings, known
in the market as Super-A and ICE, respectively.
The specimens were first steam cleaned to remove any remaining oil, dirt, and grease residue from the manufacturing
process followed by ultrasonic cleaning in grade-alcohol immersion. Once air blown to dry, the specimens were then
mounted into a vacuum chamber for pre-treatment, and finally cathodic-arc evaporation coating. The chamber was sealed
and air was pumped out to attain vacuum environment at base pressure of 1 105 mbar with the temperature simultaneously
being increased up to around 450 C. Argon gas was then introduced while the substrate specimens were biased
resulting in a glow of discharge that etched the surfaces to remove any oxide layers.
After the argon etching treatment, nitrogen gas was introduced and a bias voltage at the vertically mounted cathode arcs
called a ‘target’ vaporised the cathodes thereon depositing them onto the specimens. In the case of the monolayered TiAlN
coating, a single target comprising of titanium (33 wt%) and aluminium (67 wt%) was subjected to a 300 A bias for 2 min followed
by a 450 A bias for 40 min. As for the multilayered TiAlN/CrN coating, two targets were positioned opposite each other
in the chamber, one comprising target 1: titanium (33 wt%) and aluminium (67 wt%), the other housing target 2: chromium
(99.999 at%). Target 1 was biased at 300 A for 1 min as an initial layer, followed by 20 min of 450 A bias of both targets which
induced multilayers of TiAlN and CrN onto the substrate. The final layer was a 3 min 450 A bias on target 2. Following each
respective coating process, the specimens were left to cool in the chamber for at least 1.5 h to avoid a rapid decrease in
temperature.
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