# Surface Engineering of Woodworking Tools, a Review
## 5 Coatings Used for Woodworking Tools  
### Binary Coatings  
The first coatings applied were two-element systems. There are three main elements to synthesize protective coatings deposited on tools for woodworking: titanium [29, 46, 47, 48, 49], chromium [50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77] and carbon [39, 49, 53, 55, 56, 57]. The transition metal nitrides were the most promising solution and they did not disappoint. One of the first tests in wood machining by TiN coating was sawing the following materials: hardboard, polyvinylchloride coated particleboard, waste paper-based paperboard, plywood, and spruce. The coatings were deposited by reactive triode ion plating on tungsten carbide with the thickness varied from 0.7 to 1.0 \(\upmu\)m. The results indicated various effects on tool wear. On the one hand, when sawing hardboard and spruce, the coating reduced the wear on the rake face about 50% and 20%, respectively, compared with the uncoated tools. On the other hand, during sawing of particleboard, paperboard, and plywood, there was no increase in the durability of tools with a TiN coating [46]. This was one of the first signals that there is no universal coating. A proper coating should be selected for each treatment and type of workpiece. Additionally, other studies indicate that tool coatings can significantly improve wear resistance, especially when proper substrate preparation and proper tool geometry and cutting conditions are selected [29]. The advantages associated with the application of coatings to cutting tools are mainly high surface hardness, improved abrasion resistance, chemical inertness, and a relatively low coefficient of friction. After TiN coatings improving the durability of tools and machine parts, but also limiting applications and environment, attention was paid to chromium nitride coatings. These coatings, compared to coatings of other transition metal nitrides, are characterized by high resistance to corrosion and oxidation. Other features include high hardness and wear resistance, good adhesion of the coating to the steel substrate, high operating temperature, and a relatively low coefficient of friction [58, 59, 60, 61, 62]. A thin coating with a thickness of 2-3 \(\upmu\)m may constitute a thermal barrier limiting heat transfer to the substrate. The results of investigations conducted by [PERSON] et al. [50] indicated a significant reduction in the heat flux passing through the CrN coating, compared to the TiN coating. This was due to the nearly three times higher thermal conductivity of titanium nitride compared to chromium nitride. Single-layer CrN coatings are widely described in the literature both in the field of basic research and in applications, including woodworking. The higher resistance of the coatings to oxidation, and higher operating temperature are characterized by multi-component coatings in which one of the components is aluminum, e.g., TiAlN, forming thermally stable oxide coatings. In the cutting area, as a result of the forces acting on the blade, the oxide coating is removed and immediately, under the influence of high temperature, it is rebuilt. It would seem that the thicker the coating on the tool, the longer it will last. Unfortunately, this is not true. Research carried out by [PERSON] et al. [63] on a group of coating-substrate systems used in mechanical applications showed that thinner coatings are less susceptible to damage due to residual stresses as a result of adapting the geometric conditions at the interface. They also found that there is a critical coating thickness at which the stresses generated in it can cause the coatings to delaminate. Durability tests of WC-Co inserts with CrN and Cr\({}_{2}\)N coatings (thickness up to about 6 \(\upmu\)m) synthesized by magnetron sputtering have shown that knives with coatings 1-2 \(\upmu\)m thick have the best anti-wear properties. The service life of such tools was about four times higher than that of uncoated tools [24].