The Influence of Thermal Dilution on the Microstructure Evolution of Some Combustion-Synthesized Refractory Ceramic Composites

Modeling the self-sustained high-temperature synthesis (SHS) reaction via thermal dilution and transformation of the reaction heterogeneous media into a moderate exothermic one has unlimited potential for designing inorganic powders of a certain morphology beneficial for advanced consolidation. Thermal/inert dilution of the high-exothermic mixtures leads to the fluent decrease of both the combustion temperature and velocity, thus allowing to tailor the thermal regime of the combustion process, therewith contributing to high yield of reaction and governing the microstructural features of the combustion products. In the current review, we shed on light on the possibilities of this effective strategy to control the thermal behavior of the SHS process for the preparation of applicable powder precursors for the subsequent successful sintering. Since the SHS process of some refractory ceramics (MoSi2, TiB2, TiC, etc.) involves a relatively violent reaction rate and high combustion temperature, achieving a high level of microstructure control in these systems is often challenging. The challenge was tackled with a thermal dilution approach, attaining considerable enhancement in the homogeneity among phases with an increase of diluent content along with microstructure refinement.

Influence of Fly Ash on Corrosion Resistance of Refractory Forsterite-Spinel Ceramics

This article examines the influence of fly ash on corrosion resistance of refractory forsterite-spinel ceramics by molten iron as a corrosive medium. Fly ash in comparison with alumina were used as raw materials and sources of aluminium oxide for synthesis of forsterite-spinel refractory ceramics. Raw materials were milled, mixed in different ratios into two sets of mixtures and sintered at 1550°C for 2 hours. Samples were characterized by X-ray diffraction analysis and thermal dilatometric analysis. Crucibles were then made from the fired ceramic mixtures and fired together with iron at its melting point of 1535°C for 5 hours. The corrosion resistance was evaluated by scanning electron microscopy on the transition zones between iron and ceramics. Mixtures with increased amount of spinel had higher corrosion resistance and mixtures with fly ash were comparable to mixtures with alumina in terms of corrosion resistance and refractory properties.

ДЕТОНАЦІЙНО-ГАЗОВЕ ЗМІЦНЕННЯ ДЕТАЛЕЙ ДВИГУНІВ ВНУТРІШНЬОГО ЗГОРАННЯ

The paper deals with improving the reliability and durability of parts of the cylinder-piston group of internal combustion engines. Strengthening of machine parts is possible through the use of special production processes. Modern materials and coatings must be able to meet high operating temperatures and loads.Chrome plating, boriding and ion-plasma spraying do not meet the established quality requirements. The aluminum piston suffers damage in the head area. This manifests itself in the accumulation of cracks, channels, and traces of alloy washout. In addition, due to heating, the strength of the aluminum alloy becomes worse more than 2 times.It is proposed to create and use a coating that would withstand operating temperatures of more than 2000°C, as well as shock-pulsating loads. A detonation-gas spraying method is proposed. It is characterized by the versatility of materials and can be applied to polymers and to refractory ceramics, as well as to any metals and alloys.The deposited particles have high kinetic energy. The coating is characterized by high strength, which reaches 180 ... 200 MPa, hardness HRCe 60, and minimal cracks. The temperature effect during spraying on the workpiece is negligible. A sequence of preparatory operations is proposed. The piston and glow ring on the UN-102 detonation-gas installation were to be strengthened. A manipulator was used that uses the energy of the installation shot.The resulting surfaces are characterized by a regular macrostructure (waviness). A nickel-aluminum alloy was applied. Coating thickness was about 150 ... 270 microns, hardness was of HV 550, adhesion to the base eas of 94 ... 100 MPa. The results of studies on the parts of the cylinder-piston group showed a decrease in operating temperatures due to the running-in of the coating and high-quality sealing of the combustion chamber.The durability of the rings is 1.6·106…2.3·106, which indicates a significant increase in fatigue resistance and service life. The proposed technology is suitable and recommended for implementation in mass production