The influence of pulsed substrate bias duty cycle on the growth, microstructure, and defects of Ti1-xAlxN coatings grown by cathodic arc deposition was investigated. Ti1-xAlxN coatings of varying compositions (x = 0.56, 0.38, 0.23) were deposited on cemented carbide substrates with 10, 25, 50, and 95% duty cycles of −50 V pulsed-bias under 10 Pa of pure N2 gas. Coatings grown at low duty cycles (10 and 25%) showed strongly textured, under-dense coatings with facetted columns and low amount of lattice defects. Applying higher duty cycles (50 and 95%) produced coatings that have denser microstructures, less preferred orientation, increasing compressive stresses and increased lattice defect densities. Our study elucidates how duty cycle variation not only changes the overall average energy supplied at the growth front but also kinetically influences the coating growth and thus microstructure and defect structure.

Influence of pulsed-substrate bias duty cycle on the microstructure and defects of cathodic arc-deposited Ti1-xAlxN coatings

Tungsten carbide (WC) and Tungsten carbonitride (WCN) coatings are deposited by reactive high-power impulse magnetron sputtering (HiPIMS) with various nitrogen gas flow rates. The characteristics of discharge current and plasma optical emission of HiPIMS are recorded by oscilloscope (OSC) and optical emission spectroscopy (OES). The results exhibit that the peak discharge currents and the intensities of optical emission spectra lines are significantly influenced by the addition of nitrogen. The elemental concentration, microstructure, mechanical and tribological properties in ambient temperature and high temperature of deposited coatings are investigated by a wide variety of techniques such as energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), nano-indentation measurement, scanning electron microscope (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and ball-on-disk tribometer. The results show that WC/WCN coatings with different microstructures, mechanical properties and tribological properties have been produced by controlling the flow rate of N2. Meanwhile, with the N2 flow rate increasing from 0 sccm to 24 sccm, (101) diffraction peak shifts to low angle. Moreover, (102) and (110) peaks’ intensities and the angle of (101) peak of β-W2C phase of the deposited WCN coatings decrease and disappear, and the average grain size decreases from 8.9 nm to 6.4 nm. XPS results show that the intensities of C=N, W–N, W–C–N, and N–O peaks increase while the intensity of C–W peak decreases. The deposited coatings change from slight columnar type to a typically dense and featureless structure, and the surface roughness decreases from Ra 11.6 nm at 0 sccm to Ra 5.7 nm at 24 sccm. The variation of nitrogen flow also plays a role in the mechanical properties of the coatings. It is found that the maximum hardness and elastic modulus of 35.6 GPa and 476.5 GPa appear at 16 sccm N2 flow rate. The results of wear tests demonstrate the addition of nitrogen slightly deteriorates tribological properties at room temperature (25 °C), but can remarkably improve tribological properties at high temperature (400 °C) of WC/WCN coatings deposited with an appropriate flow rate of nitrogen.

Influences of Nitrogen Flow Rate on Microstructure, Mechanical and Tribological Properties of WCN Coatings Deposited by HiPIMS

Effects of nitrogen flow rate on the microstructure and mechanical and tribological properties of TiAlN films prepared via reactive magnetron sputtering

The residual stress plays a vital role in determination of the device performance that uses thin films coating and thus the accurate determination of stress and its optimization with process parameters is an ongoing research work for many decades. In line with this, the microscopic origin of the stress at the atomic scale and its development during the thin film deposition is a matter of major scientific interests. The development of stress is a complex phenomenon and has a complex dependence to process parameters, film microstructure and its morphology. In this work, by utilizing a custom-designed cathodic arc deposition system and synchrotron radiation based 2D x-ray diffraction (XRD) technique, we determine the real-time evolution of stress, crystallite sizes and their preferential orientations of Aluminum-Titanium-Nitride (Al x Ti 1-x N) films with varied Al-content (x=0.0, 0.25, 0.50, and 0.67) on Si-100 substrate. The energies of incoming ions and hence stress in the films is tuned by applying different direct current substrate bias (V s = floating potential, -20, -40, -60, -80, and -100 V). The instantaneous stress is evaluated by the well-known d vs. sin 2 ψ technique, while crystallite sizes are determined by analyzing line profiles of x-ray diffractograms. The evolution of stress and crystallite sizes are modelled with multiple numerical models from which kinetic parameters associated with the thin film depositions are extracted. The ex-situ microstructure characterizations of Al x Ti 1-x N coatings are carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The formation of ex-situ microstructure of the films is discussed considering the results obtained from in-situ XRD data. Finally, we demonstrate that the method utilized here is a powerful approach towards estimation of the fracture toughness of thin film coatings.

G. Håkansson

Papers

Effect of varying N2 pressure on DC arc plasma properties and microstructure of TiAlN coatings