Nanostructured surfaces

Experimental study of the characteristics of vacuum-arc multilayer coatings based on tungsten
Serdiuk I.V., Stolboviy V.O.
National Science Center “Kharkiv Institute of Physics and Technology” of the NAS of Ukraine. Str. Akademicheskaya, 1, Kharkiv-61108, Ukraine. 
E-mail: iraserduk@kipt.kharkov.ua

The development of high-level industry since the beginning of the 20th century has led to the research of more convenient materials. Superalloys solve many problems, but they create some new: the harder they are, the more difficult it is to machine them. Finding cutting tools that can resist the process of machining them enough time is a big issue. After a few seconds, the contact area between the workpiece and the cutting tool become very hot (700-1100°C) and the forces in action quickly wreck the surface of the tool. In general, very hard substrate of the cutting tool alone is not enough, and a protective layer – a coating – must be added. Chemical reactions, physical wears and the degradation process during machining is yet not fully understood and the aim of our work is to experimentally study them. Developed coatings are deposited by PVD (Physical Vapor Deposition) method and have a thickness of about 6 to 18 microns. Their properties depend strongly on technological parameters of deposition method that implies the spraying of elements from different cathodes at lower temperatures (around 350°C). We will study nitride-based multilayered multicomponent coatings like WN/NbN, WN/CrN and others. The good quality of each layers combined by doing double, triple or even multi-layers. The early-stage degradation of such protective surface can be explained in various ways including abrasive, adhesive, diffusional, chemical and oxidational processes. We have observed mechanical wears and cracks, droplets and a few case of diffusion (fig.1).

  Figure 1: Flank wear. 
  Cutting tool with WN-CrN 
  vacuum-arc coating.

         (a) flank face                  (b) 45°observation
Due to the extreme conditions encountered while turning, those processes develop almost immediately and are therefore very demanding for the tools.