Characteristics and Cutting Performance of CVD Al2O3 Multilayer Coatings Deposited on Tungsten Carbide Cutting Inserts in Turning of 24CrMoV5-1 Steel

In this work, TiN/Ti(C,N)/Al2O3 multilayer coatings were deposited using an industrial-scale thermal CVD system. Two polymorphs of Al2O3, the stable α- and the metastable κ-Al2O3, were obtained by the deposition of specific bonding layers at the Al2O3/Ti(C,N) interface. The comparable hardness and elastic moduli of α- and κ-Al2O3 multilayer coatings were measured. The tribological behavior of Al2O3 multilayer coatings was studied at room temperature using 24CrMoV5-1 balls; friction coefficients were comparable for both α- and κ-Al2O3 multilayer coatings. As a result of the relatively high hardness of coatings and the generation of abrasive wear particles, larger wear tracks were observed on balls. In Rockwell C tests, good adhesion at Al2O3/Ti(C,N)-based layer’s interface was reported in κ-Al2O3 multilayer coatings, which could be attributed to the deposition of κ-bonding layers consisting of needle-shaped grains. The cutting performances in the turning-roughing of 24CrMoV5-1 steel under different parameters—cutting speed, feed, and depth of cut—were investigated. Herein, κ-Al2O3 multilayer coatings showed the longest tool life, double of that of a commercial CVD Al2O3 multilayer coating. The results obtained could enrich the existing database for the development of prediction models of tool wear and machined surface quality and help improve tool performance for the machining of 24CrMoV5-1 steel.