This chapter is devoted to experimental research on the investigated of the structural-phase, morphology, elemental composition, physical-mechanical, and tribological properties (friction, wear, and adhesion) of hard and superhard micro- and nanostructured coatings of systems based on (Zr-Ti-Nb)N, (Zr-Ti-Cr-Nb)N, and (Zr-Ti-Cr-Nb-Si)N were fabricated by vacuum-arc deposition in the nitrogen atmosphere. The authors in the work used advanced proven experimental research methods (SEM-EDX, TEM-EDS, XRD, SIMS, GDMS, PIXE, XPS, AFM, hardness measurements, and adhesion testing), as well as theoretical methods for analysing the results. Based on the results obtained, according to the experimental data, an optimal mode was selected that provides an increase in mechanical and tribological characteristics, and a method for vacuum-arc surface hardening was also developed. Such coatings seem to have prospects as protective ones for couples of friction and cutting tools.
Top1. Introduction
High-tech industries such as: rocket and space, aviation, petroleum and gas production, as well as various alternative energy industries today pay great attention to improving the reliability and efficiency of products that are operated in various environments. The emphasis in modern materials analysis is usually directed at the structure and composition of the surface and outer layers of materials from several tens to hundreds of nanometers.
In particular, products based on titanium (Ti) and its alloys, which are used in various fields of industry, are of considerable interest due to their properties. The literature data indicate that various methods of surface treatment are used to improve the physical and mechanical properties of titanium and alloys based on it. The emphasis is on the realization that the surface and near-surface areas control many mechanical and chemical properties of solids: corrosion, friction, wear, adhesion and destruction. In addition, the composition and structure of the outer layers can be adapted using directed energy processes using lasers or electron and ion beams, as well as using more traditional methods such as oxidation and diffusion. The research of nanostructured objects is the fastest developing in modern materials science, since the ultrafine dispersed structure causes a significant improvement, and in some cases, a radical change in the properties of the material (Gavaleiro & De Hosson, 2006; Voevodin et al., 2004).
The investigation of ultrafine-grained materials has shown that a decrease in the size of crystals below a certain threshold value can lead to a significant change in properties. Dimensional effects are manifested when the average size of crystalline grains does not exceed 100 nm, and is most clearly observed when their size approaches 10 nm, and the intercrystalline (intergranular layer) is units of nanometres, consisting as a rule of an amorphous phase like nitrides, oxides and carbides (Gavaleiro & De Hosson, 2006; Nordin et al., 1998; Nordin et al., 1999; Pogrebnjak et al., 2015; Voevodin et al., 2004). From a physical point of view, the transition to the nanostate is associated with the appearance of dimensional effects, which should be understood as a complex of phenomena associated with changes in the properties of matter due to the coincidence of the size of the microstructure block and some critical length, characterizing the phenomenon as the free path lengths of electrons and phonons, the wall thickness of domains, the critical radius of the dislocation loop, etc (Morris, 1998). Conventionally, these coatings can be divided into conditionally hard (< 40 GPa) and superhard (>40 GPa), obtained using CVD (chemical vapor deposition), PVD (physical vapor deposition), magnetron sputtering and ion-assisted deposition methods (Kim & Cha, 2005; Lee et al., 2007; Leng et al., 2001; Rizzo et al., 2006; Shin et al., 2002).
Based on this, nanostructured nitride coatings based on multicomponent alloys containing at least 3-4 constituent elements are of scientific interest, and their synthesis and intensive research is an urgent task of materials science. Thus, the most diverse combination of constituent elements and changes in the physical parameters of deposition (working gas pressure and substrate bias voltage) will make it possible to change the structural state (grain size, texture, residual stresses) and properties of condensates in a wide range. Proceeding from the foregoing, the synthesis and study of nitride coatings of transition metals based on multicomponent alloys by vacuum-arc deposition is an urgent task. The analysis of the regularities of the formation of nanocrystalline coatings, the investigation of the correlation of their structural-phase state and properties depending on the deposition modes are of scientific and practical interest.
Therefore, the objective of this work is to conduct comprehensive research of the microstructure, elemental and phase compositions, surface morphology, physical-mechanical and tribological characteristics of the coating based on (Zr-Ti-Nb)N obtained by vacuum-arc deposition of the cathode, when the deposition and alloying parameters of the coating with chromium (Cr) and silicon (Si) elements change.