Papers by Author: Aelita Nikulina

Abstract: The powder of the Ni-Cr-Si-B system was applied on tubes of low carbon steel (0.2 % C) with the help of air-plasma spraying. The effect of heating temperature on the microstructure of obtained coatings was analyzed in this paper. The coatings were heated up to 500, 600, 700, 800, 900, 1000, and 1100 °C and cooled in the air. It was shown by the method of optical and scanning electron microscopy (SEM) and the X-ray diffraction analysis (XRD) that the same phases (γ-Ni, Ni₃B, Ni₃Si and Cr₂B) were present in the coatings before and after heating. Chromium carbide Cr₇C₃ was observed in the coating structure after heating to above 1000 °C. Coatings which were heated to 1000 °C consisted of grains of the solid nickel base solution, micro volumes of the Ni+Ni₃Si eutectic with inclusions of Ni₃B and particles of Cr₇C₃. The coatings which were crystallized from a liquid state (heated up to 1100 °C) consisted of large areas of the solid nickel base solution and particles of chromium carbide Cr₇C₃. The space between nickel areas is filled by the Ni₃Si+Ni₃B eutectic.

Abstract: This paper shows the results of solving a 3D problem to define types of structures and tensions which can appear during the butt contact welding process of dissimilar steels through low carbon steel inserts. The finite element method to calculate welded structures was used. The thickness of inserts was the main variable parameter. According to the results of numerical simulation using inserts can increase the reliability of welded joints between pearlitic high-carbon steel and austenitic chromium-nickel steel. The best result was obtained by using an insert with a thickness less than 20 mm. Structural studies of the welded joints between high-carbon steel and chromium-nickel steel through low-carbon inserts confirm the results of mathematical modeling.

Abstract: In this paper combined Hadfield steel - stainless steel - rail steel compounds are considered. Structural studies and estimation of mechanical properties showed that using an intermediate layer of low-carbon steel with 0.2 C wt. % and 5-20 mm thick between high-carbon steel and chromium-nickel steel in the formation of welded joints increases the reliability of connections by reducing the amount of high-strength zones as compared to compounds without a barrier layer.

Abstract: The results of structural research of welded joints between pearlitic high-carbon steel and austenitic chrome-nickel steel obtained by contact welding are presented. As a result of the diffusion process and mechanical mixing of steels local alloyed areas surrounded by pearlitic colonies of high-carbon steel are formed in the transition zone of the weld. The transmission electron microscopy (TEM) has been employed. The formation of the austenitic-martensitic microstructure occurs due to reducing the amount of alloying elements in local areas as compared to the original austenitic chrome-nickel steel chemical composition. Both austenite and martensite have crystallographic characteristics with the following orientation relationships: [211] γ-Fe || [011] α-Fe; [11-1] γ-Fe || [-110] α-Fe. The presence of high-strength local regions in the transition area may lead to a significant reduction in сrack resistance of dissimilar steels welded joints.

Abstract: Structure, microhardness and fracture features of coatings produced by atmospheric electron-beam cladding of amorphous boron were investigated. The coatings were produced by cladding of one, two and three layers of powder. Produced coatings thickness is 550, 750 and 900 μm respectively. The peak level of microhardness is 14000…16000 MPa. By the means of XRD analysis it is stated that the main phases of strengthened layers are FeB and Fe₂B borides and eutectic (α-Fe + Fe₂B). The coatings after one layer cladding have non-uniform structure with microvolumes having lack of borides. Three-layered coatings are noted for their high brittleness. The best properties are presented by two-layer coatings.