## 1 Introduction  
Because of their exceptional thermomechanical and tribological characteristics, silicon nitride-based materials are used in several applications such as cutting tools, ball bearings, sealing elements, and engine components [1, 2, 3, 4]. However, the covalent bonds betweenness-con (Si) and nitrogen (N) atoms cause difficulties in obtaining a fully dense material during sintering. Moreover, the decomposition of silicon nitride (Si\({}_{3}\)N\({}_{4}\)) starts at high temperatures (>1850 \({}^{\circ}\)C), when atomic particles become more mobile for material densification due to their low self-diffusion coefficient. Therefore, the hot-pressing method is commonly used for the fabrication of Si\({}_{3}\)N\({}_{4}\) with high density. Thus, a new class of ceramics, SiAlONs, a more cost-effective alternative to hot-pressed silicon nitride, was developed. SiAlONs are formed when silicon nitride, aluminum oxide (Al\({}_{2}\)O\({}_{3}\)), and aluminum nitride (AlN) react together. \(\alpha\)-SiAlON and \(\beta\)-SiAlON represent the two main phases of this type of ceramic. Each phase features its own properties, which can be contributed to the composites. The \(\alpha\)-SiAlON has increased hardness, whereas the \(\beta\)-SiAlON has a high level of fracture toughness. The content of these phases in composites can be adjusted and, consequently, this makes it possible to vary the properties of \(\alpha/\beta\)-SiAlON for different applications. However, the usage of ceramics on the basis of Si\({}_{3}\)N\({}_{4}\) is often limited by their poor toughness (3-5 MPa\(\cdot\)m\({}^{1/2}\)) [5]. The fracture toughness of the ceramic materials can be improved by designing composite materials reinforced with carbides, nitrides, borides, silicides, etc. [6; 7; 8; 9; 10; 11; 12; 13]. In particular, [PERSON] et al. found that the addition of titanium nitride (TiN) into SiAlON matrix can enhance fracture toughness at room temperature. They also reported that TiN presence did not have any adverse effect on densification, phase assemblage, or solid solution parameter [14; 15; 16]. In addition, the processing of ceramics is a very costly, labor-intensive, and complicated process. Only diamond tools are used for machining of this kind of materials. Based on this, it is advisable to use electrochemical processing methods, such as electrical discharge machining (EDM). This method makes it possible to avoid labor-intensive and expensive operations while maintaining high workpiece quality. However, EDM works only for electrically conductive materials. In order to be machinable by EDM, the workpieces should have an electrical resistivity of less than 1-3 \(\Omega\)-m [9; 11; 17]. The presence of reinforcement phases, which also have good electrical conductivity, can enhance the electrical conductivity of SiAlON-based composites as well, but these phases must be uniformly distributed in the ceramic matrix. Apart from the problem of distribution of the second phase, densification of these composites is very difficult due to the thermodynamic incompatibility of the incorporated phases. Based on this, the use of spark plasma sintering (SPS) appears promising. This sintering method produces fully dense ceramic composites. At the same time, the SPS temperature is lower than traditional sintering methods. This helps to avoid grain growth during the densification of materials [18; 19; 20; 21; 22; 23]. The study of tribological performance of SiAlON composites is critical because friction and wear are inherent in the machining process. There have been many reports of the wear performance of Si\({}_{3}\)N\({}_{4}\)-based composites [24; 25; 26; 27; 28; 29; 30; 31]. It was also noted that the addition of TiN phase reduces the friction due to the formation of a titanium oxide solid lubricant film and leads to a decreased wear rate of composites [32; 33; 34; 35]. So far, however, there has been little discussion about tribological properties of SiAlON-TiN composites [36; 37]. [PERSON] et al.