Tech Talk
What is Aluminum Oxide’s role in the PVD coating process?
A growing number of shops are using tools PVD-coated with TiAlN. The coating provides excellent results in applications that generate high temperatures at the cutting edge. When enough heat is generated, the aluminum in the TiAlN reacts with the oxygen in the air to create a microthin layer of aluminum oxide at the cutting surface. As this layer is created and worn away during the cutting process, it provides heat protection for the cutting tool and potentially longer life.
Many CVD coatings also benefit from a layer of aluminum oxide. Typically, it is included as one of the layers in multilayer coatings. PVD-applied aluminum oxide coatings are not available, because it is not possible to create oxides such as aluminum oxide economically using PVD equipment.
An aluminum oxide layer that is created during the coating process rather than during the cutting process performs better for several reasons. One reason is that the aluminum oxide that is created during the CVD-coating process is much thicker than the microthin layer of aluminum oxide that is generated while the tool is in the cut. Also, an aluminum oxide layer that exists in the coating before the tool begins cutting can provide heat protection with the first cut and can benefit the tool even when temperatures do not rise sufficiently to create an aluminum oxide layer on the fly.
It may be said that aluminum oxide provides the protection in both TiAlN and aluminum oxide coatings. Users must decide which use of aluminum oxide will provide the longer tool life for their applications. If the tools being used require a PVD coating, TiAlN might be the best choice for improved heat protection. If the tools can be coated using the CVD process, however, the user might achieve even higher performance by selecting a multilayer coating that includes a layer of aluminum oxide.
