The corrosion stability of pipeline steel 20 in the as received state (r) and also after quenching (q), tempering (t), and normalization (n) is studied in acetate buffers saturated with CO2 and containing 0–0.85 M NaCl. The polarization measurements and open-circuit tests showed that the corrosion resistance decreases in the following series: t ~ n > q > r. The lower corrosion rates for t and n samples are associated with the lower content of pearlite and its uniform distribution throughout the microstructure. It is shown that the preferential dissolution of ferrite during corrosion is accompanied by the pearlite component exposure and the increase in cathodic currents, which favors acceleration of corrosion.

The study covers the corrosion behavior of industrial aluminum alloy AMg6 in crevice-like gaps after various one -week exposures in tap water at a temperature of 60 degrees C. Using the metallographic analysis and scanning electron microscopy methods, it was found that in addition to the main intermetallide Al3Mg2, this magnalium also comprises Al6(Fe,Mn) and Mg2Si particles. It has been shown that local types of corrosion damage in the zone of crevice -like gaps develop with an increase in the duration of tests in the following stages: 1) active dissolution of the metal base in contact with the passive sections of the alloy and Al6(Fe,Mn) cathodic particles, which leads to the formation of hemispherical pits; 2) intercrystalline and delaminating corrosion after additional precipitation of intermetallides along the grain boundaries. The number of damages in the surface layers of the medium-alloyed magnalium for each of these local types of corrosion depends on the location of Al3Mg2 intermetallide particles released from the solid solution of magnesium in aluminum as discontinuous lines at the grain boundaries. If, prior to corrosion tests, these particles are located at the grain boundaries that are extended along the rolling direction, delaminating corrosion occurs, whereas if they do not have a distinct orientation, then intercrystalline corrosion occurs.

The nonuniformity of macro- and microstructure of low-carbon microalloyed steel pipes across their wall thickness was estimated comprehensively using optical, scanning and transmission electron microscopy. The texture of the steel was studied by X-ray diffraction analysis. Both the actual and prior austenite structures were analyzed. The possible impact of all peculiarities of the structure, namely, substructure, texture and nonmetallic inclusion as well on the cold resistance of the steel was considered and discussed. The cold resistance of steel was estimated based on the ductile-brittle transition temperature (DBTT) determined in using Сharpy impact tests performed in a wide temperature range (from ambient and subzero temperatures). Correlations between the structural features of samples, which were cut from the near-surface areas of steel pipes and at the pipe-wall midthickness, and the DBTT were found. The high nonuniformity of ductility was demonstrated, which can be characterized by the fact that the DBTT of midthickness areas of pipe wall exceeds that of near-surface areas by 30°. The lower DBTT (the higher cold resistance) corresponds to the steel characterized by thin (less than 20 ​μm) fragmented lath-like bainite bands.

X-ray structure analysis and metallography are applied for investigations into the phase composition and structure of powdered model alloys Co-9.2% C and Co-1% Mo-9.2% C after various treatments (mechanical doping, thermal treatment, sintering) and plasma coatings produced from these powders. It is demonstrated that carbides Co x C y are formed within mechanical doping and plasma spraying, which are absent in the equilibrium state diagram. High microhardness of plasma coatings (up to 8.3 GPa) is associated with formation of carbides and amorphous phase. Carbon losses at stages of plasma spraying of coatings are determined.

•Oxide inclusions do not affect active dissolution but weaken passivation.•Varying the steel microstructure has little effect on active steel dissolution.•Passive currents and breakdown potentials are sensitive to steel microstructure.•Increase of the sulfur content in steel results in weaker passivation.•Voltammetric parameters can be used to predict corrosion behavior under open circuit.

80 wt % hydroxyapatite + 20 wt % calcium carbonate composite powders have been synthesized through precipitation from aqueous solutions. Increasing the ripening time of the precipitate in the mother liquor leads to partial calcium carbonate dissolution and the formation of carbonate-substituted hydroxyapatite and improves its crystallinity. In addition, the specific surface area of the powders increases from 83.2 to 238.7 m(2)/g. The powders ripened for 14 and 21 days show the best sinterability.

Materials in the hydroxyapatite (HA)-calcium carbonate (CC) system were synthesized by a precipitation method from aqueous solutions. According to the data of X-ray phase analysis and IR spectroscopy, the powders consisted of CC and AB-type carbonate-substituted HA (CHA). In order to determine the content of carbonate-containing phases in materials, the temperature-temporal mode of fractionated-combustion analysis of carbon was developed. The quantitative phase ratios and the degree of substitution of carbonate groups in CHA were determined. It was shown that the degree of substitution of carbonate groups in CHA increased from 2.47 to 5.31 wt % as the CC content increased from 13.50 to 88.33 wt %.

Pipes made from steels 19G, 17GS, 17G1S, 10G2FBYu, 13G1S-U, and 20KT of various manufacturers and technologies are studied. Electron microprobe and fractional gas analyses are used to determine the main types and number of nonmetallic inclusions (NIs). The effect of a modification procedure on the oxidic cleanness of steel 20KT (produced at JSC "Volzhskii Pipe Works") is studied. The use of a silicocalcium-filled wire is shown to increase the total contamination of the steel by nonmetallic, in particular, calcium aluminate and magnesium spinel inclusions, which are conditionally related to corrosion-active non-metallic inclusions (CANIs). Fractional gas analysis is shown to allow the number of oxide inclusions of various types to be accurately determined in pipe steels. No correlation is found between the volume fraction of oxide inclusions determined by fractional gas analysis and the number of CANIs determined by a metallo-graphic method.

Hydroxyapatite/calcium carbonate (CC) composite powders containing up to 50 wt % CO 3 2− , have been prepared via precipitation from aqueous solutions. According to chemical analysis data, the CO 3 2− content of the powders coincides with the intended one over the entire composition range studied. With increasing CO 3 2− content, the specific surface area of the powders decreases because of the formation and growth of large needlelike CC crystals up to 1.5 μm in size. The addition of low-melting-point alkali carbonates to the starting powder mixture reduces the sintering temperature of the powders to below 720°C, thereby preventing the thermal decomposition of CC. The highest bending strength, up to 76 MPa, is offered by the materials with the lowest CC content, about 20 wt %, and an average crystal size of 100 nm. The solubility of the composites gradually increases with CC content. In vitro experiments with a human fibroblast model (MTT test) demonstrate that the composites have zero cytotoxicity.