The formation of second phases with a high aspect ratio (whiskers, fibers, platelets) in the structure of the material is an effective method of increasing the fracture toughness of ceramic materials. The paper presents the results of determination of the fracture toughness of ceramics based on Al 2 O 3 and ZrO 2 with the addition of 3 wt.% SrAl 12 O 19 (SrA 6). Experimental samples were prepared according to the following technology: dispersion of water suspensions in a bead mill, spray drying granulation, hydrostatic pressing and free sintering. Submicron powders of α-Al 2 O 3 (CT3000 SG), 3Y-TZP (Stanford Materials) and SrO were used as raw materials. X-ray diffraction analysis revealed the presence of three phases in sintered ceramics: α-Al 2 O 3 , t-ZrO 2 and SrAl 12 O 19. Structural investigations were carried out using scanning electron microscopy. It has been determined that the size of SrAl 12 O 19 platelets in alumina ceramics is 1.2 × 0.2 µm. The addition of 20 wt.% ZrO 2 leads to an increase in platelet sizes up to 2.5 × 0.5 µm. However, this also leads to a decrease in the number of SrAl 12 O 19 grains. The dimensions of the platelets are 0.8 × 0.2 µm in the material with 85 wt.% ZrO 2. Therefore, it has been determined that an increase in the content of ZrO 2 affects the platelets sizes. The fracture toughness by indentation under a load of 5 kg is calculated by the Niihara formula. It has been found that the presence of SrAl 12 O 19 leads to an increase in the fracture toughness by 1.2 −1.6 times. The maximum value has been obtained for material 80(Al 2 O 3-3SrA 6)-20ZrO 2. The study of the propagation of crack growth allows revealing inter-and transgranular fractures. The crack propagation path changes upon collision with a perpendicular oriented platelet of SrAl 12 O 19. At the same time, there is a realization of the mechanism for increasing crack resistance due to the deviation of the path of the propagating crack. Another mechanism is associated with the dissipation of energy due to the destruction of the platelets.
Abstract. The structure, mechanical and tribotechnical properties of medium-carbon steel doped with 0...9 wt. % of copper with the 1% increment were investigated. During this study, the structural changes in the alloy with an increase of the copper amount were analyzed. Increase of the copper amount in the structure of medium-carbon steel leads to the gradually refinement of the ferrite grains and perlite components. In the samples doped with 9 wt. % of copper the tertiary cementite was found at the boundaries between ferrite grains and the colonies of lamellar perlite. The ε-Cu phase was revealed using X-ray diffraction of the cast steel with ~ 3 wt. % of Cu. Further increase of the copper amount promotes the increase of ε-Cu volume fraction. The change in hardness and wear resistance with an increase in the copper amount in medium-carbon steels was detected. The samples doped with ~ 6 wt. % of copper showed the maximum wear resistance at the non-fixed particles condition that corresponds to the hardness of material 240 HB.
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