# Surface Engineering of Woodworking Tools, a Review
## 5 Coatings Used for Woodworking Tools
### Multilayer Coatings
The coating design process should take into account the type of material being processed, the machining parameters, and the type of tool to be used. Nevertheless, based on the results presented in Tables A1-A3, it can be noted that:  
* A comparison of various coatings operating in the same conditions shows the advantage of CrN both in the treatment of beech wood [53] and OSB [24; 71];
* Worse performance properties of Cr\({}_{2}\)N coatings compared to CrN [24; 84] were confirmed, which may be caused by their greater brittleness and worse adhesion to the substrate;
* A comparison of the wear resistance of single-layer coatings was presented by [PERSON] et al. [85]. Binary CrN and ternary AlCrN and TiCN coatings deposited on WC-Co tools (substrates) during the milling of oak wood showed improved wear resistance of cutters by factors of 3.0, 1.9, and 1.7, respectively. They also found that CrN was characterized by the best adhesion among the tested coatings and a low and stable coefficient of friction. They stated that low-friction coatings exhibited better wear resistance;
* Ti-based coatings have inferior wear resistance compared to Cr-based coatings. This applies to both magnetron- and arc-formed coatings. The Ti-W-N/Ti-W coating is characterized by twice the tool wear area compared to the Cr-W-N/Cr-W coating in the milling of OSB and particle board [41]. The wear of the tool covered by TiCN and CrN coating is smaller by 1.6 and 2.0, respectively [57; 65]. The above conclusions are confirmed by [PERSON] et al. [85];
* Multilayer coatings have better properties compared to single-layer coatings. CrN and CrN/CrCN coatings were deposited on a substrate made of M2 steel and cemented carbide and the timber boles were rounded [54]. Two significant effects were observed: (a) The multilayer coating was characterized by a greater wear resistance of about 170%, while in the case of CrN coatings the increase was about 100%. These results relate to the tests carried out on the M2 steel tool coating system. Cement carbide tools with coatings were characterized by a slightly lower durability of approx. 110% (CrN/CrCN) and 100% (CrN). It should be noted, however, that uncoated tools made of M2 steel rounded 15 boles, and cemented carbide tools 188 boles; (b) The comparison of these coatings shows that in M2 steel tools with CrN/CrCN coatings the service time is about 33% higher compared to the CrN coating, and in the case of a cemented carbide tool the increase is about 7% [54]. This confirms the reports of many authors about the importance of the substrate;
* A comparison of the edge recession of tungsten carbide tools with TiAlN monolayer coating and TiAlN/TiSiN and TiAlN/TiBON multilayer coatings in milling different wood composites indicates a greater edge recession of the TiAlN and TiAlN/TiSiN coatings [81]. Among the tested coatings, the smallest edge recession was demonstrated by the TiAlN/TiBON multilayer coating, despite the fact that its hardness was the lowest among the tested coatings, 2700 HV. The TiAlN/TiSiN coating, with a hardness of 3600 HV and the highest coefficient of friction (0.9), showed greater edge recession than the TiAlN single-layer coating. The results of these tests confirm that a lower coefficient of friction is more important than hardness.