Structure And Properties Of Magnetron Sputtering VC-Co Film

Hard coatings of transition metal carbides have been widely studied for various applications, but the low toughness limits its service life and application in many other fields. Therefore,improving the toughness of hard coatings is very important. Many of these efforts have been devoted to improving the coating toughness by alloying with Group VIII metals. We hope that the ductilule material can retard the crack extension, finally, improving the toughness of the coatings.This paper proposed and successfully tested a new coating design, In the microscopic scale, the structure is using the ductile phase (Co) package the hard phase (VC) to improve the ability of resisting crack of the coatings under the premise of enough hardness. Through the component control (Co doping amount) and process control (change of substrate bias) to adjust the toughness, to obtain the coatings with high hardness and high toughness.We have prepared VC coating and a series V-C-Co coatings using non-reactive magnetron co-sputtering from VC and Co targets, study the effect of Co content to the structure and the mechanical properties of those coatings, and discuss the mechanism of the improving of mechanical properties. In addition, this paper also study the effect of different substrate bias to the microstructure and mechanical properties of those coatings.The main contributions of this paper are as follows:1) VC was crystallized in all of the coatings while Co was amorphous.2) With the addition of Co, the plastic index of the coatings is obviously improved, while, the hardness is reduced, when the Co content is close to12.4at.%, the mechanical properties of the coating was the best, right now, the hardness close to21Gpa, and the plasticity index close to0.53. The comparison of indentation morphology and the crack growth trends also proved that, the toughness of the coatings have been improved after joining Co.3) A nanocomposite microstructure, in which amorphous ligament-like Co-rich regions partially separate the nanocrystalline VC grains, was observed in the coatings with12.4at.%Co by TEM under300℃. This structure may well hinder crack initiation and propagation, and accord with our initial ideas. At the same time, XPS analysis of the same coating reveals a noticeable charge transfer from Co2p states to C1s states, pointing to the formation of a strong Co/VC interface which block the initiation and propagation of crack.4) With the increasing of substrate bias, the columnar growth structure has no obvious change. The comparison of indentation morphology and the trend of crack propagation show the toughness of the coatings have been significantly improved. At the same time, the nanoindentation results show the hardness of the coatings was not obviously decreased. Therforer, increasing of bias can improve the toughness in the basic of maintain it’s high hardness.