No 2 (2026): Frontier Materials & Technologies

Abstract: Problem. Intergranular corrosion (IGC) is one of the most dangerous types of corrosion affecting chromium-nickel austenitic steels. With low degrees of IGC damage, the dimensions of the affected surface zones are small, making them reliably detectable only through metallographic examination, which reduces the efficiency and reliability of inspection. Objective. To evaluate the feasibility of increasing the reliability of testing austenitic steels for susceptibility to intergranular corrosion by applying the acoustic emission (AE) method during testing. Methods. The object of study was 12Kh18N9 austenitic steel. Specimens of the steel were subjected to various heat treatments and corrosion treatments to induce intergranular corrosion with varying degrees of damage. The specimens were then tested for resistance to IGC according to GOST 6032–2017 using a static three-point bending test, in which the acoustic emission method was applied in addition to the standard test procedure. Results. The application of the AE method during mechanical testing of austenitic steel specimens made it possible to detect IGC even at low levels of corrosion damage, This was achieved through an up to tenfold increase in AE activity and an increase in AE pulse amplitudes from 60 dB to 90 dB. Moreover, the AE method allows the identification of the sensitised state of austenitic steel by detecting an increase in the proportion of hits with amplitudes exceeding 50 dB (from 0.046 to 0.155), without requiring additional metallographic examination. Conclusions. The AE method can be used during testing of austenitic steel specimens for resistance to IGC to improve the reliability of results, since AE parameters differ significantly between specimens in the initial state, those in the sensitised state, and those with pronounced IGC.

Abstract: Problem. Despite the uniquely high long-term rupture creep of 114 MPa at temperature of 650 °C for 100,000 hours of the new advanced creep -resistant 10Kh10K3V2MFBR steel, its practical application is limited by the lack of technologies for producing high-quality permanent joints. Traditional fusion welding technologies lead to degradation of mechanical properties due to hydrogen embrittlement, formation of -ferrite, and porosity. Objective. To determine experimentally the main aspects of microstructure formation (phase composition, phase morphology, martensite crystallography) and mechanical properties (hardness and strength) of 10Kh10K3V2MFBR steel after friction stir processing (FSP) with high heat input, as well as to establish the reasons for hardening in the stir zone and softening in the heat-affected zone, in order to assess the suitability of this steel for friction stir welding. Methods. Plates of 10Kh10K3V2MFBR steel 3.2 mm thick after normalization at 1060 °C and tempering at 770 °C were subjected to FSP using the parameters of 800 rpm – 5 mm/min. Optical metallography, SEM, EDS, and EBSD methods were used to reveal the mechanisms of microstructure formation in the stir zone (SZ) after FSP. Results. The possibility of producing a material with a fully martensitic structure in the processing zone and a minimal softening effect in the heat-affected zone after FSP was established. It was found that FSP with the parameters of 800 rpm – 5 mm/min leads to heating of the material in the stir zone above the Ас3 temperature (>985 °C). The extreme thermomechanical conditions of FSP contributed to the refinement of the prior austenite grains from 35 to 10 μm. The formation of a fine-grained martensitic microstructure, as well as mechanical alloying with wear products in the stir zone, contributed to an increase in microhardness from 230 to 420 HV in the center of the stir zone and to ≈760 HV on the advancing side of the stir zone. After FSP, the yield strength decreased by 55 MPa, the ultimate tensile strength decreased by 30 MPa, and the percentage elongation decreased by 6 %. Conclusions. High-temperature FSP of 10Kh10K3V2MFBR steel ensures the formation of a martensitic microstructure but is accompanied by intensive wear of the hard alloy tool and a reduction in tool service life.

Abstract: Problem. Cold-resistant chromium-nickel stainless steels possess low strength properties. Their replacement requires using steels with enhanced strength characteristics and lower cost. Steels alloyed with nitrogen and carbon meet these requirements; however, their crystal structure at low temperatures has been insufficiently studied. Aim. To determine the influence of low temperatures and low-temperature deformation on the crystal structure parameters of a nickel-free austenitic steel with a high content of interstitial elements. Methods. The crystal structure of cast CrMnCN steel with a (С+N) content of 1.27 wt. % was investigated by X-ray diffraction methods in the temperature range from −190 to 20 °C. The steel was preliminarily homogenised at 1000 °С, then heated to 1150 °С and quenched in water. Tensile tests were carried out at temperatures from −196 to 20 °С. After testing, the crystal structure was analysed. Results. After quenching, the dendritic structure of the steel consists of austenite with a lattice parameter а=3.6405 Å and clusters of dispersed particles. Upon cooling of the steel, the FCC lattice parameter decreased, while in specimens tested in tension, it increased as the test temperature decreased. At cryogenic test temperatures, the crystal lattice exhibits auxetic behaviour. During cooling and low-temperature deformation, stacking faults (SFs) form in the steel. After testing at −196 °С, the SF concentration is twice as high as in steel cooled to the same temperature. The combination of low ductility of the steel at −196 °С, a small amount of plastic deformation work, and a high dispersion of coherent scattering regions (CSRs) indicates the onset of martensitic transformations. Conclusions. Upon cooling of the steel, the lattice parameter decreases. Conversely, during low-temperature deformation, the FCC lattice parameter increases, and at −196 °С the steel exhibits auxetic behaviour. A feature of the response of the crystal structure to low-temperature deformation is an increase in the SF concentration and a small CSR size.

Abstract: Problem. The low ductility of binary Fe-Ga alloys significantly limits their thermomechanical processing capabilities and industrial application as magnetostrictive materials. Although alloying with rare-earth metals improves performance characteristics, the influence of temperature and hot deformation conditions on the behaviour of Fe-Ga-based alloys has been insufficiently studied, which prevents the optimisation of technological regimes for manufacturing sheet products without the risk of fracture and the formation of undesirable microstructures. Aim. To determine the influence of hot deformation temperature (700, 850, and 1000 °C) on the deformation behaviour, microstructure, and crystallographic texture of Fe80Ga20 alloys with additions of 0.1 and 0.2 % Ce, and to establish the optimal hot deformation temperature. Methods. The binary Fe80Ga20 alloy and two doped (Fe80Ga20)99.9Ce0.1 and (Fe80Ga20)99.8Ce0.2 alloys were studied. Physical simulation of hot rolling was carried out using a Gleeble 3800 simulator under plane strain conditions at temperatures of 700, 850, and 1000 °C with a strain degree of 75 %. The structure and texture were studied using optical metallography and scanning electron microscopy with EBSD analysis. Results. The addition of cerium significantly improves the ductility of the alloys at temperatures of 850 and 1000 °C. At 700 °C, intense strain hardening and crack formation are observed in all alloys. At 1000 °C, intense grain growth and the formation of a heterogeneous structure occur. The differences in the behaviour of the alloys with 0.1 and 0.2 % of Ce are insignificant. Conclusions. Cerium alloying significantly improves the ductility of the binary Fe80Ga20 alloy. The optimal hot deformation temperature for Fe-Ga-Ce alloys is 850 °C.