Comparison of Al–Si–N nanocomposite coatings deposited by HIPIMS and DC magnetron sputtering

Abstract

This paper presents a comparative study between DC magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HIPIMS) of Al–Si–N. Coatings were synthesised through co-sputtering of Al and Si in a mixed Ar/N2. One set of DCMS experiments and one set of hybrid HIPIMS (Al-target)/DCMS (Si-target) experiments were conducted. It was found that a higher partial pressure of N2 was necessary to obtain fully nitrided material using the HIPIMS process. The Si content of the samples was varied between 0 and 16at.%. All processes were characterised using optical emission spectroscopy (OES) as well as energy-resolved mass spectrometry (E-MS). The obtained coatings were characterised using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), as well as UV–Vis spectroscopy and nanoindentation.The HIPIMS processes were found to provide a highly activated growth environment, with Al+ comprising 87% of the total ion flux, compared to 0.6% for the DCMS case, where Ar+ was found to be the dominating species comprising 90% of the total ion flux. Coatings from both HIPIMS and DCMS processes were found to form nanocomposites of a solid solution phase (Al1-xSix)N and most likely a SiNy phase, as shown by XRD and XPS analyses. Compared to coatings from DCMS, samples deposited with HIPIMS had a slightly more textured AlN-phase with smaller grains, as well as smoother and, denser morphology as observed by SEM.In agreement with previous studies, the coatings had a high transparency in the visual and near IR range; an optical band gap (E04) between 4.6 and 5.2eV and a refractive index between 1.9 and 2.1 was observed. The ternary coatings studied here were found to be hard with the HIPIMS coatings (combined average 22±3GPa) being harder than their DCMS counterpart (combined average 17±1GPa). A maximum hardness of 27GPa was observed for the sample deposited with HIPIMS and a Si-content of 7at.%.