Effect of growth conditions on the mechanical properties of lanthanum-gallium tantalate crystals

The effect of growth conditions, anisotropy and polarity of specimens on the mechanical properties of lanthanum-gallium tantalate La3Ta0.5Ga5.5O14 single crystals grown in different atmospheres (argon (Ar), argon with oxygen addition (Ar+(<2%)O2 and Ar+(2%)O2) and air) was studied. The test specimens for the measurements were cut perpendicularly to a 3rd order axis (Z cuts) and in polar directions perpendicular to a 2nd order axis (Y cuts). The polarity of the Y cut specimens was tested by piezoelectric response. The brittleness was evaluated by microindentation at 3, 5, 10 and 25 g loads. The brittleness proved to show itself at a 5 g and the higher loads regardless of growth atmosphere. Therefore microhardness tests were done at loads of within 3 g. The microhardness HV of the specimens was measured with an DM 8B Affri microhardness tester by Vickers methods. The hardness H, elastic modulus E and elastic recovery coefficient R were measured with a Berkovich pyramid on a CSM Nano-Hardness Tester using the instrumented indentation (nanoindentation) method. Growth atmosphere was shown to affect the mechanical properties of lanthanum-gallium tantalate crystals: crystals grown in an oxygen-free argon atmosphere had the lowest microhardness, hardness, elastic modulus and elastic recovery coefficient. The lowest microhardness was detected in Z cut specimens regardless of growth atmosphere. The mechanical properties of polar Y cuts proved to be anisotropic: the microhardness, hardness, elastic modulus and elastic recovery coefficient of these cuts were lower for positive cuts than for negative ones regardless of growth atmosphere. Y and Z cut langatate specimens grown in argon with less than two percent oxygen exhibited strong elastic modulus and elastic recovery coefficient anisotropy

POSSIBILITIES FOR IMPROVING THE SURFACE QUALITY OF STRUCTURAL STEELS, INVAR AND TITANIUM ALLOYS THROUGH REACTIVE ELECTROSPARK TREATMENT WITH ELECTRODES OF AN ALUMINUM-SILICON ALLOYS

In the rough and semi-pure processing of metal alloys, as well as in additive technologies, surface defects are often observed - the appearance of scratches, creases, recesses, incisions, pores, ridges, protruding particles, and other unevenness, undesirable spiral or concentric relief, traces of cutting edges of the tool and high roughness on the treated surface. In this work, the possibilities for improving the surface characteristics of materials such as steels, invar and titanium alloys with typical surface defects through reaction electrospark deposition (ESD) are investigated. A study of the conditions for the local formation of reactive phases and reduction of surface roughness during the electrospark modification was performed. Layering electrodes of low-melting Al-Si alloys were used. Their choice was made on the assumption that a liquid melt is formed in the process of ESD. It is expected that it will fill the recesses, pores and scratches and interact with the chemical elements contained in the substrate. The results of the studies of the change in the roughness, thickness and microstructural characteristics of the modified surfaces depending on the energy of the pulses and their influence on the wear resistance at friction are presented. A double effect has been achieved - a significant improvement in both the surface characteristics and the wear resistance of the modified surfaces. It was found that the improvement of surface quality and wear resistance was achieved as a result of partially burning the protrusions, filling the depressions with low melting electrode alloy and local synthesis of wear-resistant surface structures and phases obtained by the chemical interaction of the melt with the substrate. The energy parameters of the electric discharges, the process parameters, and the ESD conditions, suitable for the realization of the above phenomena, have been determined and optimized

ADDITIVE METAL PROCESSING TECHNOLOGIES - PROBLEMS AND WAYS OF LEVELING THE SURFACE DEFECTS

This work provides an overview of the technological features of additive technologies for manufacturing metal parts and products (3D printing metals). The nature and types of printing, perspectives, and opportunities for their development are indicated. The advantages and disadvantages of additive technologies are clarified. An analysis of the technological process parameters has been made, on the basis of which the main problems hindering its mass introduction in the industry have been identified. The main dependencies of the quality and properties of the manufactured parts on the process parameters are given, and ways of avoiding and eliminating the defects are presented

ELIMINATION OF IRREGULARITIES AND DEFECTS ON STEEL SURFACES THROUGH ELECTRO SPARK SURFACE MODIFICATION WITH ALUMINUM ALLOYS

The surface roughness of the parts has a significant influence on their performance properties and it is crucial for the friction force and wear of the bodies. Therefore, in practice it is often necessary to perform finishing treatment to reduce the macro, micro and meso- roughnesses - grinding, honing, lapping, polishing and more. In this study are examined the possibilities of reducing the roughness and the traces of the previous machining of steel surfaces by electro-spark deposition (ESD) with low-melting aluminium alloys. The roughness of the steel surfaces obtained after different milling modes after subsequent electrospark coating was investigated. Dense and uniform coatings with different surface microgeometry are obtained, which to a different extent erase the traces of the preceding processing. The examination of tribological characteristics showed a significant increase in the wear resistance of the coated surfaces. The process parameters and materials for ESD at which coated surfaces have simultaneously the lowest roughness and the highest wear resistance have been determined and optimized