Deposition and characterization of TiAlN/Si3N4 superhard nanocomposite coatings prepared by reactive direct current unbalanced magnetron sputtering

Superhard nanocomposite coatings of TiAlN/Si3N4 with varying silicon contents were synthesized using reactive direct current (DC)13; unbalanced magnetron sputtering. The Si and TiAl targets were sputtered using an asymmetric bipolar-pulsed DC power supply and a13; DC power supply, respectively, in Ar+N2 plasma. The structural and mechanical properties of the coatings were characterized using13; X-ray diffraction (XRD) and nanoindentation techniques, respectively. The elemental composition of the TiAlN/Si3N4 nanocomposite13; coatings was determined using energy-dispersive X-ray analysis and the bonding structure was characterized by X-ray photoelectron13; spectroscopy. The surface morphology of the coatings was studied using atomic force microscopy. The XRD data showed that the13; nanocomposite coatings exhibited (1 1 1) and (2 0 0) rexFB02;ections of cubic TiAlN phase. The broadening of the diffraction peaks with an13; increase in the silicon content in the nanocomposite coatings, suggested a decrease in the average crystallite size. The TiAlN/Si3N413; nanocomposite coatings exhibited a maximum hardness of 43 GPa and an elastic modulus of 350 GPa at a silicon concentration of13; approximately 11 at%. The hardness and the elastic modulus of the nanocomposite coatings decreased signixFB01;cantly at higher silicon13; contents. Micro-Raman spectroscopy was used to characterize the structural changes as a result of heating of the nanocomposite13; coatings in air (400x2013;850 1C) and in vacuum (900 1C). The Raman data of the nanocomposite coatings annealed in air and vacuum showed13; better thermal stability as compared to that of the TiAlN coatings. Similarly, the nanocomposite coatings deposited on mild steel substrates exhibited improved corrosion resistance.13