Deposition and characterization of TiAlN/Si3N4 superhard nanocomposite coatings prepared by reactive direct current unbalanced magnetron sputtering
Harish C. Barshilia, B. Deepthi, K.S. Rajam
Vacuum
Abstract
Superhard nanocomposite coatings of TiAlN/Si3N4 with varying silicon contents were synthesized using reactive direct current (DC) unbalanced magnetron sputtering. The Si and TiAl targets were sputtered using an asymmetric bipolar-pulsed DC power supply and a DC power supply, respectively, in Ar+N2 plasma. The structural and mechanical properties of the coatings were characterized using X-ray diffraction (XRD) and nanoindentation techniques, respectively. The elemental composition of the TiAlN/Si...More3N4 nanocomposite coatings was determined using energy-dispersive X-ray analysis and the bonding structure was characterized by X-ray photoelectron spectroscopy. The surface morphology of the coatings was studied using atomic force microscopy. The XRD data showed that the nanocomposite coatings exhibited (11 1) and (200) reections of cubic TiAlN phase. The broadening of the diffraction peaks with an increase in the silicon content in the nanocomposite coatings, suggested a decrease in the average crystallite size. The TiAlN/Si3N4 nanocomposite coatings exhibited a maximum hardness of 43GPa and an elastic modulus of 350GPa at a silicon concentration of approximately 11at%. The hardness and the elastic modulus of the nanocomposite coatings decreased signicantly at higher silicon contents. Micro-Raman spectroscopy was used to characterize the structural changes as a result of heating of the nanocomposite coatings in air (400 8501C) and in vacuum (900 1C). The Raman data of the nanocomposite coatings annealed in air and vacuum showed better thermal stability as compared to that of the TiAlN coatings. Similarly, the nanocomposite coatings deposited on mild steel substrates exhibited improved corrosion resistance.
keywords:TiAlN/Si3N4 superhard nanocomposite coatings; Structural and mechanical properties; Thermal stability; Corrosion behavior; Unbalanced magnetron sputtering
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