Research On The Superhardness Mechanism Of Superhard Nanocomposite Films

Nanofilm with the hardness more than 40GPa is commonly intituled superhard nanocomposite films. It has no columncrystalline structure like monolayer film. It is quite prominent for improving the performances of hard flim and has extensive applicable foreground. Therefore, the preparation of superhard nanocomposite films is attented the focus by people. In the patterns of plating nanocomposite films, the means of magnetron sputtering is currently used for making superhard nanocomposite films like nanonitride adding compound(such as TiN/Si3N4, TiN/NV, TiN/NbN, TiC/TiB2) or nanonitride adding metal(nc-MeN/M, Me is Ti,Zr,V,Nb, M is Cu,Ni,Y,Ag,Co). But the research of preparing triumphantly superhard nanocomposite films with the pattern of nc-MeN/M by multi-arc ion plating technique that is applied most widely in industrial manufacture is rare reported.In this paper, with the technical pure Ti and Cu targets multi-arc ion plating technique was used for plating TiN/Cu superhard nanocomposite multilayer films through adjusting the unlocking interval time of Cu target, lighting time of plating Cu and the relative place between smples and targets and preparing TiN-Cu composite films by plating together. The appearance, structure of phase, preferred orientation and microhardness of composite films were researched by SEM, XRD, EDS, Nanoindentation, and primarily discussed the mechanism of super hardness.The results of this experiment show that it can prepare TiN/Cu superhard nanocomposite multilayer films whose hardness is 51GPa by multi-arc ion plating technique. TiN/Cu nanocomposite multilayer films are observed obvious lamination,and there is clear limit between layer and layer. The structure of every layer is very exiguous column crystals, and the thickness of every layer is different along with the difference of the plating technological parameters. The hardness of composite multilayer films is approximately 50%~150% higher than that of pure TiN film, and ascertained together by content of Cu, unlocking interval time of Cu, preferred orientation and so on.When other technological parameters are changeless, the hardness of composite multilayer films is influenced by unlocking interval time and lighting time of Cu target. And the hardness augments first and minishes after with increasing of unlocking interval time and lighting time of Cu target. Generally speaking, films obtain easyily tiptop hardness when Cu target is been lighting for 10 or 15 seconds, unlocking interval time of Cu target is 2~3 minutes namely the thickness of monolayer film is 119~286nm; composite multilayer films obtain superhardness (>40GPa)when lighting up Cu target every three minutes for 10 seconds. So the composite multilayer films obtain easyily upper hardness when unlocking interval time and lighting time of Cu target arrive in optimal range.In X-ray diffraction (XRD) pattern, the diffraction peaks are broaded markedly, and the crystal grain size is smaller. Accounting by Scherrer equation, it is showed that the grain size of TiN in (111) and (200) crystal face is less than 20nm at large and the size in (220) crystal face is mostly less than 10nm, forming nanocrystal grain, consequently coming into being surperhard result by grain refinement.Preferred orientation of TiN is disturbed by mixing into Cu element. TiN phase does not orient in (111) single crystal face any more, but orients along (220) single crystal suface, grows with two preference crystal face of (111) and (200), or has no obvious orientation. The hardness is low-rise (between 20GPa and 30GPa) when film orients in (220) single crystal face; the hardness is comparatively bigger (>30GPa) when film grows in (111) or (200) single crystal face; and the films gain superhardness(>40GPa) when TiN grows with two preference crystal faces of (111) and (200).Furthermore, this experiment prepared TiN-Cu co-deposition composite films by plating together using the approximately same technological parameters with continuous arcing. The result shows that the cross-section of TiN-Cu co-deposition composite films by this measure is smooth and it is formed by incalculable small grains. The grain size is less than 15nm, achieving the level of nanocrystal. This co-plating measure can also enhance hardness of single TiN film. And the hardness is influenced weightily by the content of Cu. If the content of Cu is too much, surface objection will be too much and the hardness will decline rapidly.