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Silver, silver alloys, and composites with silver matrix are used mainly as electric contacts, circuit-breakers, and slide bearings. Contacts working conditions require as high as possible thermal and electrical conductivity, wear resistance during electric arc work, low susceptibility to tacking, and chemical stability. Unreinforced silver alloys do not meet those expectations, hence increasing interest in metal matrix composites. Reinforcing with ceramic particles improves tribological wear resistance and minimizes formability of silver alloys. At the same time, introduction of ceramic particles decreases thermal and electrical conductivity. In this paper, manufacturing method of silver-based composites reinforced with particles Al2O3, SiC, and glassy carbon was described. Composites were subjected to differential thermal analysis. Furthermore, thermal diffusivity measurements using laser flash method, as well as measurements of linear thermal expansion coefficient using dilatometric method were performed in order to determine heat conductivity of the prepared composites.

A new type c-c¢ Co-Al-Mo-Nb Co-based superalloys were developed due to limitations of basic Co-Al-W superalloys, related to tungsten alloying. The present study aims to characterization of new c-c¢ Co-10Al-5Mo-2Nb (at.%) cobalt-based superalloy performance in terms of the high-temperature exposure under cyclic conditions, with particular regard to surface condition. Specimens were tested in cycles of hightemperature exposition (25, 50, 75, 100 and 150 h) in air environment at 800°C. Detailed analysis of oxidized surfaces by scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction was made at various intervals during testing. The cyclic oxidation behavior of new alloy was compared to the basic Co-9Al-9W (at.%) Co-based superalloy.

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The c-c 0 Co-based superalloys are newly developed class of refractory alloys which may replace commercial Ni-based superalloys owing to their favorable properties at high temperature. In case of new Co-based superalloys, the heat treatment aims to obtain microstructure composed of appropriate volume fraction of small cuboidal c 0 -Co 3 (Al,W) precipitates within the c-Co matrix. However, due to a high tendency to interdendritic segregations of alloying elements, the alloys based on Co-Al-W system should be normally homogenized before further steps of heat treatment (solutionizing and aging). In this study, thermal analysis was applied for determination of temperature range for primary heat treatment of the Co-9Al-9W (at.%). The differential thermal analysis (DTA) measurements were carried out on the thermal analyzer NETZSCH STA 449 F3 Jupiter. On the base of obtained results, respectively, solvus of c 0 phase and solidus temperatures were determined, as well as the thermal range of Co 3 W (DO 19 ) phase precipitation. As a consequence, the heat treatment without homogenizing (only solution and aging) was proposed as a most suitable way to obtain beneficial microstructure.

In this investigation, the thermal analysis of W-free cobalt-based superalloys based on Co–Al–Mo–Nb and Co–Ni–Al–Mo–Nb systems was performed. The analysis was performed at different stages of heat treatment process. The differential thermal analysis (DTA) was utilized for the determination of characteristic temperatures related to microstructural changes. First of all, the DTA analysis was carried out for discussing as-cast alloys in the temperature range of 40–1500 °C. The results showed thermal effects connected with melting and important order–disorder transition. The temperature range of 1200–1250 °C was chosen for performance of a first heat treatment operation for the investigated alloys. Specimens were annealed at selected temperature for 5 h. The microstructure of alloys after solution heat treatment was analyzed as well. Afterward, the solutionized specimens were subjected to the further thermal analysis in order to select the aging temperature according to the order–disorder transformation related to formation of γ′ phase with overall formula Co3(Al,X). Five aging variants were performed in the temperature range of 800–1000 with a step of 50 °C. After each stage of heat treatment, SEM/EDS analysis and hardness measurements were performed.

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