The TiN thin film coating has now been superceded in many applications by the TiAlN or AlTiN coating. The colour is of the TiAlN coating is dependent on the Ti:Al ratio within the coating and can range from black to bronze. TiAlN offers superior performance for a range of metal machining and fabrication applications. The reason for this lies in the addition of aluminium to TiN or specifically the formation of aluminium oxide on the surface of the tool which increases the operational temperature range of the coating to 800 deg.C compared with 500 deg C for TiN. As the TiAlN coating is heated in air a thin layer of amorphous aluminium oxide forms on the surface of the coating, which protects the coating from further oxidation.
This results in better hot hardness than most other coatings. In many high speed turning operations TiAlN outperforms TiN or TiCN because of the protective oxide layer. This has recently been increased by the addition of chromium and yttrium or vanadium to the coating increasing the temperature range to beyond 900 deg.C. The TiAIN coating is also tough resulting in a reduction in coating chipping.
TiAlN coating – Applications
The properties of the TiAlN coating make it suitable for high temperature cutting operations with minimum use of lubricant or dry machining. TiAlN is used successfully to machine titanium, aluminium and nickel alloys, stainless steels, alloy steels, Co-Cr-Mo and cast irons. TiAlN is also used to protect dies and moulds that are required to operate at high temperatures such as those in medium and hot forging and extrusion industries.