Microstructure and mechanical properties of cathodic arc ion-plated (Al,Ti)N coatings

Cathodic arc ion-plated (Al,Ti)N coatings were deposited on WC–Co substrates by several bias voltages. The residual stress of the films, measured by the X-ray diffraction (XRD) 2θ–sin2 ψ method, was found to vary significantly with the negative bias voltages. The composition and microstructure of the films were investigated by electron probe microanalysis and transmission electron microscopy, respectively, and these were also changed by the bias voltages. The changes in composition and microstructure were related to the film strains induced by ion bombardment, and were evaluated by the peak shifts and half-value widths of XRD profiles. At higher bias voltages, the films were mainly composed of granular structures with a size of 100 nm. With the decrease of negative substrate bias voltage, the microstructure changed to a columnar structure with a column size of 120 nm. Carbide drills deposited with (Al,Ti)N coating with lower bias voltages showed better cutting performance in the machining of carbon steel compared with those deposited with coating under high bias voltages. The wear resistance of drill margins is critical for the drilling performance in this test, and the dense columnar (Al,Ti)N films with low strains showed greatly improved wear-resistant characteristics of the drills.