Russian Metallurgy (Metally)最新文献

Abstract—The use of effective technologies and high-quality materials and the reduction of production costs are the main challenges for competitive domestic agricultural and automobile transport enterprises; therefore, the renovation of car parts and agricultural machinery from high–quality secondary materials is a priority direction in their development. The purpose of this work is to study a coating formed by plasma–powder deposition of a powder created by the electroerosion dispersion of R18steel waste. (Experimental) 40Kh steel rounded samples 40 mm in diameter are used as a substrate for plasma–powder surfacing. Scanning electron microscopy is used to determine the elemental composition of the formed coating. An Olympus GX51 optical microscope is used to determine porosity. The Vickers microhardness of the samples is determined using a DM-8 automatic microhardness analysis system. The friction coefficient of the surface of a plasma–powder coated sample was measured on a special-purpose Tribometer friction machine. (Results and discussion) The results of tribological tests of the friction surface of samples made of 40Kh steel and a plasma–powder coating from a mixture of 50% PZhV5 iron powder and 50% R18 steel waste powder indicate a high friction coefficient of the latter. The wear is characterized by smoothing the solid surface protrusions of a sample. (Conclusions) The equal ratio of PZhV5 and R18 powders in the mechanical mixture is found to be optimal. The main elements of the plasma–powder coating formed at this ratio of powders in a mechanical mixture are iron, oxygen, carbon, tungsten, and molybdenum. The average microhardness of the 40Kh steel base is 2.1 times lower than that of the coating. At a path of 500 meters, the average friction coefficient of the deposited coating is 0.146 and that of the base is 0.486.

The causes of destruction of a thermal barrier coating on gas turbine engine turbine blades are studied, and the mechanism of its destruction has been revealed. A method for inhibiting the mechanism of oxide film growth at the ceramic layer–metal sublayer interface decomposition is presented. An improved metallic sublayer is proposed for the restoration of gas turbine engine turbine blades with allowance for their operational damage. The results of comparative studies of the heat resistances and thermophysical properties of various coatings are presented.

Abstract—Nickel–cobalt alloys are widely used in the modern technology. Manganese is one of alloying components in these alloys. Oxygen is a harmful impurity in the Ni–Co alloys and exists in the metal in both the dissolved state and as nonmetallic inclusions. The presence of oxygen in the alloys leads to the degradation of their service characteristics. The study of the thermodynamics of oxygen solutions in melts of this system is of considerable interest for the practice of alloy production. A thermodynamic analysis of oxygen solutions in the manganese-containing Ni–Co melts is carried out. The equilibrium constant of the reaction of manganese with oxygen dissolved in the nickel–cobalt melts, the activity coefficients for infinite dilution, and interaction parameters in the melts of different compositions are determined. When manganese reacts with oxygen in the Ni–Co melts, the oxide phase contains NiO and CoO along with MnO. The mole fractions of MnO, NiO, and CoO in the oxide phase for different manganese contents in the Ni–Co melts at 1873 K are calculated. In the case of the nickel melt already at the manganese content higher than 0.1%, the mole fraction of manganese oxide is close to unity. The mole fraction of manganese oxide in the oxide phase decreases as the cobalt content in the melt increases. In the case of pure cobalt, the mole fraction of MnO is close to unity at the manganese concentrations higher than 0.7%. The dependences of the solubility of oxygen in the melts under study on the cobalt and manganese concentrations are calculated. In the nickel–cobalt melts, manganese is characterized by a high oxygen affinity. The deoxidizing ability of manganese decreases with increasing cobalt content in the melt and is significantly lower in pure cobalt than in pure nickel. The curves of oxygen solubility in the manganese-containing nickel–cobalt melts pass through a minimum, the position of which shifts toward higher manganese concentrations as the cobalt content in the melt increases.

The formation of the phase composition and structure in a quenched titanium alloy based on the Ti₂AlNb intermetallic compound with an initial hydrogen content and with 0.3 wt % hydrogen is studied during isothermal holding at temperatures of 950 and 1000°C for 10–300 min. The introduction of hydrogen into the alloy is shown to decrease the decomposition intensity of the metastable B2 phase under the temperature conditions under study. When the isothermal holding temperature decreases to 950°C, the decomposition dynamics at various hydrogen contents intensifies, which leads to a decrease in the volume fraction of the β phase by 10% compared to holding at 1000°C. After high-temperature isothermal treatment, the decrease in the microhardness of the alloy is not significant, and the microhardness is only 10–30 HV_0.05 less than the values obtained for the quenched single-phase state.

Abstract—Production technology of an Ti–10Nb–(1–3)Mo alloy has been developed. The effect of heat treatment conditions on the structure, microhardness, and impurity composition of ingots is studied. The optimum conditions of homogenizing annealing (950°C for 12 h), which results in leveling the chemical composition and the formation of completely recrystallized structure, are determined. After annealing, an increase in the microhardness and the homogeneous chemical element distribution over the entire volume takes place. After melting, the alloys comprise the α'/α"- and β-Ti phases; after annealing, the α-, β-, and ω‑Ti phases are present. The oxygen, nitrogen, and carbon contents correspond to regulations for titanium alloys. According to fractional gas analysis (FGA) data, the titanium oxide content dominates over the niobium and molybdenum oxide contents.

Modern gas turbine engines operate under changing temperature loads; therefore, one of the important characteristics of the protective coatings of turbine blades is their high resistance to the appearance and development of cracks under mechanical and thermal loads. The effective internal heat removal systems used to cool turbine blades lead to an increase in their thermal stresses. Currently, thermal fatigue cracks are among the common defects in the protective coatings of turbine blades. The heat resistance of the coatings at high temperatures is determined by the following three factors: the shape of the part onto which a coating is applied, the coating thickness, and the phase composition of the surface layers or the maximum aluminum content in a coating. Therefore, when a protective coating is chosen under these operating conditions, it is important to know the influence of these factors on the heat resistance of a coating. In this work, we compare the cracking resistances of various coatings during cyclic temperature changes. The heat resistances of the coatings are found to depend on the method of application and their phase-structural state. The revealed mechanism of formation and propagation of thermal fatigue cracks depending on the phase composition of an initial coating is especially important. The life of the protective coatings under cyclic temperature changes is shown to depend on the chemical composition of a coating and the method of its formation. The dependence of formation of thermal fatigue cracks on samples with the coatings under study on the number of temperature change cycles has been revealed.

The results of experimental studies aimed at studying the dependence of the adhesive strength of a coating plasma sprayed onto the cylindrical surface of a part on the spraying conditions are presented. Correlation and regression analyses of the data on the effect of the deposition conditions on the adhesion of the coating are carried out in order to reveal multicollinear relationships.

Abstract—The influence of alloying elements and heat-treatment conditions on the fracture toughness of precipitation-hardening nonmagnetic vanadium-containing steels has been studied. The causes of formation of microductile intergranular fracture in steels, the structure of which contains precipitate-free zones, are revealed. Alloying of Mn-containing steels with nickel is found to increase K_1c; the introduction of chromium in Mn–Ni steels in an amount of more than 3% leads to a decrease in K_1c. The heat-treatment conditions forming a fine-grained structure with fine VC and VN particles in an amount of 0.5–1.0 wt % is shown to provide maximum K_1c.

The influence of preliminary plastic tensile deformation (ε_pd = 9.5–26%) on the low-cyclic fatigue (LCF), phase composition, and residual stresses of 0.3- and 0.8-mm thick VNS9-Sh TRIP steel ribbons is determined. The LCF resistances of the ribbons of both thicknesses are shown to decrease as ε_pd increases. Cyclic loading is found to lead to the formation of tensile stresses in martensite, unlike static tension inducing compressive stresses in martensite.

Abstract—The parameters of the shock-compressed gas that forms between plates under their collision during explosive welding are investigated. A photosensor is used to determine the shock wave front velocity at a contact point velocity V_c = 1900–2600 m/s; this velocity is found to be ≈1.3V_c, which is higher than that calculated using a Hugoniot adiabat (≈1.2V_c). Ultrafine (50–200 nm) metallic particles, which form from a dispersed cumulative jet in the welding gap, are found to affect the shock wave front velocity substantially. Low-inertia thermopiles were used to determine the heat flow (≈0.24 GW/m²) induced by the action of the shock-compressed gas on the plate surface before a collision at a distance of 0.4–1.3 m from the beginning of welding, which made it possible to calculate the temperature of heating the surface layers of the plates before a collision.