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The paper presents and discusses questions on structure formation during the sintering process of Cr2O3-based composites using the hot pressing method, when a chemical reaction between the components takes place. The task was difficult because Cr2O3 decomposes when sintered at temperatures above 1300 °C. The proposed novel method allowed for interaction between aluminum and chromia, thus avoiding the decomposition of the latter. Here, ultrafine aluminum powder played the role of the active agent forming a liquid phase and reacting with Cr2O3. The appearance of the solid solutions of (Cr,Al)2O3 with different stoichiometry of Cr and Al depended on the aluminum content in the initial mixture. The solid solution significantly strengthened boundaries between composite phases, resulting in the composite material of high fracture toughness between 5 and 7 MPa m½ and bending strength of ca. 500 MPa. The best mechanical properties exhibited the cermet with 22 wt.% of the restored chromium. [ABSTRACT FROM AUTHOR]

The areas of use of a slotted spring are given in the work by examples of applications from the point of view of modernity and the promising development of technological structures. With the advent of the design of a slotted spring in the middle of the last century, its calculations were usually limited to calculation for compression-stretching. Torsion and bending in complex loads were neglected, stipulating this in the calculation assumptions. In connection with modern high-precision applications of a slotted spring in aerospace engineering and nuclear power, more rigorous calculation approaches are needed. For this purpose, the analytical dependences of the calculation of a slotted spring on the torque are derived. The accepted design scheme uses the generally known provisions of the theory of resistance of materials and this is illustrated in detail by author's sketches. As in the traditional approaches to calculating a slotted compression-tension spring, the outer rings are considered as separate semi-rings with fixed ends. The contribution of the associated bending of the rings and the displacement of the bridges are taken into account in calculating the total torsion angle in the proposed solution of the stress-strain state of a slotted spring under the torque load. [ABSTRACT FROM AUTHOR]

Fabrication of alumina–tungsten carbide nanocomposite was investigated. Characteristics of the densification and sintering were analyzed considering both the nano-size particle starting powders and the processing stages. Different heating rates were generated during densification and consolidation with a maximal load was applied only after a temperature of 1000 °C was reached. Due to the varying dominance of different physical processes affecting the grains, appropriate heating rates and pressure at different stages ensured that a structure with submicron grains was obtained. With directly applied alternating current, it was found that the proportion Al2O3 (50 wt.%)–WC provided the highest fracture toughness, and a sintering temperature above 1600 °C was found to be disadvantageous. High heating rates and a short sintering time enabled the process to be completed in 12 min, saving energy and time. [ABSTRACT FROM AUTHOR]