The object of this study is structural formation during the surfacing of steel (iron) on titanium with plasma-sprayed coatings to obtain a butt connection of titanium-steel bimetallic plates. The task to be solved was to devise a technology for applying a barrier layer between titanium and steel to obtain a defect-free butt joint of the edges of bimetallic sheets of carbon steel, clad with a layer of titanium, under conditions of arc or plasma surfacing of carbon steel on titanium. The application of the barrier layer was carried out by plasma spraying of steel wire or iron powder. In this case, a coating with a thickness of 150...750 μm was applied on Grade2 titanium, on which 1–2 mm thick layers of materials similar to the sprayed ones were deposited by arc and plasma deposition. It was established that during spraying with subsequent surfacing of steel wire or iron powder, the main technological factors for eliminating cracks in the resulting compound are the thickness of the sprayed coating and the amount of linear surfacing energy. The thickness of the sprayed coating was selected (at least 400...600 microns) followed by plasma surfacing of ER70S-6 steel wire with a diameter of 1.0 mm or CNPC-Fe200 iron powder with unit energy up to ~200...250 J/mm. A defect-free transition layer from titanium to steel was obtained. It is a continuous layer with a thickness of 50–60 microns, consisting of intermetalides FeTi and FeTi2, as well as a β-phase titanium with an enhanced iron content, which retains certain ductility without cracks and other defects. With the help of the devised approach for connecting titanium-steel bimetallic edges, it is planned to manufacture seam bimetallic pipes for main pipelines to transport oil and gas raw materials extracted from wells.

Existing techniques for applying intermetallide layers are characterized by low productivity, difficulties associated with the maintenance and operation of technological equipment, as well as significant costs for the purchase of materials for spraying. Therefore, modern science shows considerable interest in the development of new, highly effective technologies to form intermetallide coatings on the surface of articles. Such promising techniques include the technology of plasma-arc spraying (PAS) of flux-cored wires. This technique has a number of significant advantages, namely high performance, relative simplicity, as well as the affordability of equipment and materials for coating. This paper reports a study into the structure and properties of coatings obtained by flux-cored wire PAS, in which the steel sheath and aluminum powder filler interact when heated with the exothermic effect of Fe3Al synthesis. The influence of technological parameters of PAS process on the structure and properties of Fe-Al coatings was investigated by means of mathematical planning of the experiment. It was found that in all samples the main phase is an intermetallide of the Fe3Al type. Tests for gas-abrasive wear resistance at room temperature showed that the wear resistance of coatings exceeds the stability of steel S235 by an average of 2 times. As a result of studying the electrochemical properties in a 3-% aqueous solution of NaCl and in a 0.5-% solution of H2SO4, the score of corrosion resistance for these media was determined, which was, respectively, 4 and 5 (coatings belong to the group of "resistant"). In this regard, the practical use of coatings based on the Fe3Al intermetallide is recommended for protection against oxidation, corrosion, and gas-abrasive wear of components and assemblies in the heat power industry (heat exchanger pipes, catalytic converters, steam turbine blades, shut-off valves, etc.)