The conventional vacuum arc coating technology yields Al–Ti– Si–N coatings where the “metallic” silicon is dissolved within the (TiAl)N crystals forming a metastable (Al,Ti,Si)N solution。(11) The hardness of these coatings of 34 GPa is somewhat lower than that achieved with the
5
nc-(Al1−x Tix )N/a-Si3N4 nanocomposites of ≥40 Gpa。
Nevertheless, also
these coatings showed a better cutting performance than the conventional
(11)
(Al1−x Tix )N ones when applied to ball-nosed carbide end-mills。
The development of the nc-(Al1−x Tix )N/a-Si3N4 industrial coatings in 1994 was motivated by the work of Li Shizhi et al。(12) In parallel
to the development of the materials, also the new coating technology based on rotating arc cathodes was developed because of the requirement for uniform erosion of that cathode and high-density plasma。 Accord- ing to the generic design principle(9, 10) these conditions are needed for the formation of the nanocomposites with a high thermal stability and
5The value of the hardness reported in [11] might be somewhat underestimating the real one because of the relatively small thickness of the coatings of about 4 µm。 However, in an earlier patent DE 195 17 119 Al of these researchers similar hardness of about 32 GPa was reported for 10 µm thick coatings。
also to evaporate pure aluminium that is not possible with conventional cathodes。 This technology was recently included into a new advanced coating system π 80 that utilizes lateral rotating ARC cathodes LARC® technology developed by SHM together with the company PLATIT (Switzerland)。 The asymmetric arrangement of the cathodes with respect to the coated tools provide automatically a nano-layered structure of the coatings and enables a pre-cleaning of the cathodes by means of Virtual Shutter® that significantly improves the performance of the coatings。 This enabled us to significantly improve the cutting performance。 Examples will be presented in order to demonstrate that the nano-layered-nanocomposite nc-(Al1−x Tix )N/a-Si3N4 coatings display excellent cutting performance that is superior to the state-of-the-art (Ti1−x Alx )N coatings。
2。THE DEVELOPMENT OF THE COATING TECHNOLOGY
According to the generic principle for their design,(9, 10) the for- mation of the nanocomposites with a high thermal stability requires a sufficiently high chemical activity of nitrogen in order to assure the seg- regation of stoichiometric phases, such as nc-(Ti1−x Alx )N and a-Si3N4。 This is achieved in an intense plasma at a sufficiently high nitrogen
pressure。(9, 10) A deposition temperature of ≥500◦C is required in order to
make the thermodynamically driven and diffusion rate controlled segrega-
tion to proceed fast。 Because such conditions are rather difficult to achieve in conventional PVD coating systems with planar electrodes, SHM devel- oped a new vacuum arc technology based on a central cathode。
Figure 1 shows schematics of the axially symmetric central cath- ode consisting of two independent segments, one made of pure titanium and the other one of AlSi alloy of the eutectic composition of 11。8 wt (11。3 at%) of Si。 The axially symmetric magnetic field together with the perpendicular electric field at the cathode provides the Lorenzian force which results in a fast rotational movement of the cathodic spot on the surface around that axis。 By an appropriate change of the axially symmet- ric magnetic field in the axial direction, the arc can be moved from one segment to the other one with a frequency of the order of kHz。 In such a way, atomically mixed (Ti1−x Alx )N/a-Si3N4 coatings of a chosen stoichi- 新型超硬纳米复合材料英文文献和中文翻译(2):http://www.youerw.com/fanyi/lunwen_92149.html