## 1 Introduction  
The very rapid development of composite materials has been observed over the last few decades which often offers unexpected possibilities for modeling the properties of products. A wide range of composites are metal matrix composites strengthened with reinforcement in the form of particles, fibers, or flakes [1, 2]. Powder metallurgy technology, as one of the few techniques, enables the formation of metal composites with expected properties [2, 3]. The application of this technology allows, for example, the elimination of problems occurring in the casting technique related to poor wettability of ceramic particles by liquid metal or the heterogeneous distribution of the reinforcement in the matrix [4, 5, 6]. An interesting group of metal composites is the copper matrix composites. Copper is the main candidate for such applications because it has the highest thermal conductivity among the construction materials [7, 8]. Materials made of copper-based alloys and composites are irreplaceable in metal joining technology [9, 10]. Materials bonding is a field of material engineering in which an important role is played by resistance welding processes that are used to join elements in the automotive, household appliance, or aerospace industries. Electrodes are used in welding processes to exert pressure and supply current. They are required to have a high electrical and thermal conductivity, high softening temperature, high hardness at welding temperature, and low manufacturing costs [11; 12]. High-durability electrodes are a highly desirable product of great importance and application in the industry [13; 14]. The most durable electrodes available on the market are copper electrodes strengthened with dispersion aluminum oxide (Al\({}_{2}\)O\({}_{3}\)), manufactured using powder metallurgy technology. Copper compounds reinforced with ceramic particles such as SiC, Al\({}_{2}\)O\({}_{3}\), B\({}_{4}\)C, and TiC can also be produced by friction stir processing [14; 15]. Research results indicate that copper composites with a high content of TiC reinforcing particles have good mechanical properties, such as hardness and wear resistance, while density and thermal conductivity drastically decrease. Therefore, composites with a TiC content below 5% by volume are used for applications such as spot-welding electrodes and sliding contacts [16; 17]. An increase in mechanical properties and abrasion resistance was also confirmed in copper composites with the addition of carbon nanotubes [18]. Moreover, an investigation of copper matrix composites reinforced with ceramics in the form of TiB whiskers and TiB\({}_{2}\) particles showed that the composite containing 0.9% (\(w\)/\(w\)) TiB whiskers and 1.0% (\(w\)/\(w\)) TiB\({}_{2}\) has higher strength and higher electrical conductivity compared to a composite containing only 2.6% (\(w\)/\(w\)) TiB\({}_{2}\) particles [19]. It is extremely important that introduced ceramic particles are not dissolved in the matrix because it may significantly reduce the electrical conductivity of the composite. In Cu-SiC composites, such a negative effect can occur due to the silicon dissolution process in copper [20]. In order to avoid phase changes at the metal-ceramic boundary, it is possible to cover the ceramic particles, e.g., with tungsten and nickel coatings [21; 22]. Tuff is a type of hard rock with high porosity. It consists of pyroclastic material (principally sand and volcanic ash) most often with an admixture of other crumb materials which they are cemented with, for example, a silica or clay binder [23; 24; 25]. Tuff also includes clay minerals and zeolites; in their structure, there are empty tubular spaces with a ground clearance of several A [23; 24; 25]. Based on our previous studies, it was found that the material that can be used to strengthen copper is volcanic tuff from Filipowice, Poland. It consists of porous aluminosilicates with a developed surface, containing a series of hard and refractory oxides [23].