## 1 Introduction
Figure 1: Technology life cycle in the field of laser technology used in materials science. It is also possible that some of the introduced powder dissolves in the silver matrix via diffusion and thus increases the stresses occurring in the microstructure, creating a solid solution combined with the undissolved part of the metal powders used. This causes an increase in the stresses occurring in the material, e.g., due to the strengthening with second-phase particles, which is most often described by two mechanisms: the Orowan-Ashby and Mott-Nabarro or Friedel mechanisms [13; 14]. Therefore, from the scientific perspective, one of the most important research aims was the investigation of the microstructure and enhancement of the mechanical properties; additionally, improvements in the hardness of the surface are very important for practical use. The microstructure and its compounds were investigated using the Ag-Cr and Ag-Ni equilibrium diagrams. The structure is a double system in which eutectics occur with limited mutual solubility of both metals. The determination of the laser treatment parameters is also important, particularly the laser power, to achieve a high value of layer hardness to protect the new developing material from losing its properties and to make the tool surface more resistant. Furthermore, EDS microanalysis was applied to determine the chemical composition of the created surface layer [15; 16; 17; 18; 19; 20]. The silver alloys used in different transportation branches, e.g., for switches, show some disadvantages mainly concerning their low hardness and, relatedly, wear resistance. Therefore, the first aim in our study was enhancing the hardness of the surface layer to extend its lifespan without compromising its electrical properties. For this, metallic powders were used instead of ceramic particles (WC, NbC, VC), which could increase the electrical or thermal properties of silver. DSC analysis was applied to determine the thermal stability of this alloy, as well as the melting point shift and value compared to the pure Ag basis used [21; 22]. Silver alloys are generally characterized by low strength, relatively low density, intermediate thermal stability, and creep resistance, with promising mechanical properties at elevated temperatures when combined with other phases fed into the surface layer. The introduction of nickel and chromium via laser treatment into the Ag matrix can increase the mechanical, tribological, and corrosion properties of the composite layers through the presence of undissolved Cr particles, as well as the formation of intermetallic Ni phases. For alloying, both powders were used in a 1:2 mixture because of the lower solubility of nickel in silver (approx. 3%) compared to chromium (approx. 6%). The assumption was that these powders with the silver matrix create diverse types of intermetallic phases, significantly enhancing mechanical properties such as coherent or semi-coherent phases. Preliminary research and a review of the literature have shown that the introduction of Cr and Ni into the molten pool during surface alloying forms a hard and wear-resistant layer on the surface of the aluminium alloy [23; 24; 25; 26; 27; 28; 29]. In this study, the effect of the added alloying elements on the microstructure and hardening was analysed. The mechanical properties of the zones of the surface layer were evaluated by employing microhardness and adhesion tests, as well as by characterizing its depths and surface quality. To avoid the formation of coarse particle conglomerates on the surface, the mechanical properties were improved and the optimal treatment parameters were proposed. Another aim of the conducted research was to investigate the microstructural changes and mechanical properties after laser remelting and/or alloying with the addition of Cr/Ni metal powder.