Microstructural control of TiC/a-C nanocomposite coatings with pulsed magnetron sputtering

In this paper, we report some striking results on the microstructural control of TiC/a-C nanocomposite coatings with pulsed direct current (DC) magnetron sputtering. The interface morphology and microstructure evolution as a function of pulse frequency and duty cycle were scrutinized using atomic force microscopy, scanning electron microscopy and high-resolution transmission electron microscopy techniques. It is shown that, with increasing pulse frequency, the nanocomposite coatings exhibit evolutions in morphology of the growing interface from rough to smooth and in the microstructure from strongly columnar to fully columnar-free. In addition, the smoothly growing interface favors the formation of a tailor-made multilayered nanocomposite structure. The fundamental mechanisms are analyzed with the assistance of plasma diagnostic experiments. Ion mass/energy spectrometry measurements reveal that, depending on the frequency and duty cycle of DC pulses, pulsing of the magnetrons can control the flux and energy distribution of Ar+ ions over a very broad range for concurrent impingement on the growing interface of deposited coatings, in comparison with DC sputtering. The significantly enhanced energy flux density is thought to be responsible for the "adatom transfer" in interface smoothening and thus the restraint of columnar growth. (C) 2007 Acta Materialia, Inc. Published by Elsevier Ltd. All rights reserved.