The paper presents the results of a study on the microstructure and mechanical properties of a mediumcarbon steel (0.45 % C) processed by severe plastic deformation (SPD) via high-pressure torsion (HPT). Martensite quenching was first applied to the material, and then HPT processing was conducted at a temperature of 350°C. As a result, a nanocomposite type microstructure is formed: an ultrafine-grained (UFG) ferrite matrix with fine cementite particles located predominantly at the boundaries of ferrite grains. The processed steel is characterized by a high-strength state, with an ultimate tensile strength over 2500 MPa. Special attention is given to analysis of the thermal stability of the microstructure and properties of the steel after HPT processing in comparison with quenching. It is shown that the thermal stability of the UFG structure produced by HPT is visibly higher than that of quenchinginduced martensite. The origin of the enhanced strength and thermal stability of the UFG steel is discussed.
The quality of coating on the high-silicon aluminum alloy Al-12%Si depending on the initial microstructure of the samples has been investigated. The method of microarc oxidation (MAO) has been used for coating. The quality of coating was evaluated by the thickness and microhardness of the formed layer. The initial microstructure of aluminum alloy samples was varied by distribution of silicon particles in the volume of the matrix solution. The possibility of obtaining a high-hardness protective coating on the alloy Al-12%Si by the MAO method has been shown. The influence of the alloy microstructure on the microhardness and thickness of coatings has been established. It has been shown that the deformation thermal treatment of Al-12%Si alloy samples before MAO leads to deterioration in the quality of the formed layer. A model of the influence of the silicon particles distribution on the quality of the micro-layer has been represented for explanation of the observed effect. The increase of microhardness in coatings with a greater thickness has been revealed.
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