# Surface Engineering of Woodworking Tools, a Review
## 2 Tool materials  
Due to machining conditions, cutting tools should be characterized by high resistance to mechanical loads and high temperatures. In the case of metal processing, frictional heat can increase the temperature in the cutting zone to 700 \({}^{\circ}\)C [10], but during wood processing and especially the processing of wood-like materials, the temperature exceeds 800 \({}^{\circ}\)C, which results from high friction forces in the machining zone [11]. Such temperature occurs both on the rake surface and the clearance surface, and has a significant impact on the wear rate of the cutting tool. The main parameters which ought to be taken into account are: chemical inertness and stable physical properties, including hardness at high temperatures, low wear ratio for different wear mechanisms, and sufficient toughness to avoid material fracture [12]. The history of the development of tool materials used for wood (wood-like materials) and metal processing is similar. Tool steels were applied as the first materials; they were relatively soon replaced by high-speed steels. The increased interest in wood-based material processing and related problems resulted in the introduction of composite tools based on hard, fine WC particles sintered with cobalt. Co is responsible for the elastic bounding of hard WC particles. By selecting the size of hard particles and the amount of bonding phase, the mechanical properties of sintered tools can be changed. Another group of tool materials is stellites, characterized by high hardness depending on the chemical composition (36-52 HRC), and high resistance to abrasion and high temperatures (up to 950 \({}^{\circ}\)C). In the early 1980s, one of the most modern tools was sintered carbide. After the dramatic question \"Is there life after tungsten carbide?\" [13], the answer was almost immediate, with \"PCD replacing carbide in woodworking applications\" [14]. At this time, there was an abrupt increase in interest in modified woodworking tools. The polycrystalline diamond (PCD) displaced traditional steel and cemented carbide tools in woodworking [15; 16; 17; 18]. The significantly better strength and tribological properties of PCD, such as hardness (about 40-50 GPa, compared to 10-22 GPa for carbides) and low coefficient of friction, meant it could enable an increase in durability and minimize the machine downtime of tools. This meant that PCD tools offered considerable potential for cost savings in the machining of wood and wood-like materials. [PERSON] indicated [15] that the life ratio of PCD tools compared to carbide cutters was about 17:1. Only its price forced the search for new solutions. These were the thin hard coatings deposited on tools' working surfaces. The application of tools with modified hard coatings for metalworking resulted in an abrupt increase in production capabilities and product quality. Knowledge of the research and exploitation of the coatings for metalworking tools cannot be fully adopted in woodworking. This is related to the differences in their structures and properties, including mechanical properties, coefficients of thermal conductivity, roughness, and absorption of various substances. This results in the need to design new coatings that meet market expectations. Due to the hygroscopicity of wood and wood-like materials, an application of cooling and lubricating agents is excluded. It seems that the best perspective to adopt is the improvement of tool durability by surface modification. [PERSON] [19], in one of the first literature reviews of wood cutting tool wear, indicated the problems with the measurement of edge dulling. He stated that tool wear deals primarily with the tool material, with the work material, and with tool-work interactions, and the chemical nature of wood may play a large part in cutting tool wear. [PERSON] et al. [20] summarized wood machining over the last 50 years in France. They found that tool wear depends on the cutting process parameters, and kind and quality of timber. Coating technologies may improve tool life.