Improved mechanical performance and structural properties of bias induced reactively sputtered Si doped TiAlC nanocomposite coatings

Si doped TiAlC nanocomposite coatings consisting of nanocrystallineTiC phase embedded in amorphous matrix of a-C/a-Si/a-Al4C3 have been deposited on stainless steel and silicon (100) substrates using four cathode reactive unbalanced direct current magnetron sputtering at Tsub= 300οC. The effects of substrate bias ǀVbǀon the microstructure, surface morphological, compositional, mechanical and frictional properties have been carried out by using X-ray diffraction (XRD), field-emission scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, nanoindentation hardness tester and nano-scratch measurements. XRD analysis reveals that the coating exhibits fccNaCl type TiC (111) preferential orientations. Moreover, micro-Raman spectroscopy study indicates the existence of graphitic rich layer of a-C in the coating as the bias voltage increases. Substrate bias causes a subsequent change in the microstructure from fine granular to a denser morphology. High rate of ion bombardment induces a transformation from columnar to a non-columnar microstructure as the bias voltage increases. Coatings prepared at an optimum ǀVbǀ=50 V, exhibit the excellent hardness and Young’ modulus value of ~ 33 and 280 GPa, respectively. The friction co-efficient measurements show a decrease from ~ 0.55 to 0.24 as the bias voltage increases from ǀVbǀ= 25 to 150 V