Machining performance and decomposition of TiAlN/TiN multilayer coated metal cutting inserts

The wear resistance of metal cutting inserts coated with metastable Ti0.34Al0.66N/TiN multilayers was tested in continuous turning of an AISI 316L stainless steel. The multilayers had periods of 25 + 50, 12 + 25 and 6 + 12 nm (Ti0.34Al0.66N + TiN) with a total multilayer stack thickness of 2 μm. Inserts coated with monolithic TiN and Ti0.34Al0.66N deposited under similar conditions were used as references. The multilayer coated inserts show a decrease of wear with decreased multilayer period, both on the rake and flank face. The wear on the rake face was lower on all the multilayer coated tools compared to the references. Scanning transmission electron imaging and energy dispersive spectroscopy elemental mapping of a worn multilayer coating show decomposition of the Ti0.34Al0.66N to domains rich of Al and Ti. High resolution transmission electron micrography shows preserved epitaxy between the TiN and Ti0.34Al0.66N layers. The improved wear resistance of the multilayer coated inserts is discussed in terms of an improved thermal stability of the multilayer stacks.