Materials Science最新文献

The kinetic characteristics of thin-sheet (approx. 1 mm) Zr–1%Nb alloy samples after treatment in a carbon-containing gas medium (({P}_{mathrm{Ar}+{mathrm{C}}_{3}{mathrm{H}}_{8}}) = 0.106 Pa) in a wide temperature range of 650–850°C and time 1; 5 and 10 h were investigated. The carburizing of the alloy at temperatures of 650 and 750°C occurs according to a law close to linear (n ≈ 1), and at 850°C according to a law close to parabolic (n ≈ 2). The activation energy of the alloy carburizing in the temperature range of 650–850°C at the propane partial pressure ({p}_{{mathrm{C}}_{3}{mathrm{H}}_{8}}) = 0.018 Pa was 2.21 kJ/mol. The distribution of microhardness and structure of the near-surface layers of the alloy was shown. The microstructure of the near-surface layers of the alloy after carburizing was determined. The α-Zr and ZrC phase content on the alloy surface after treatment in a carbon-containing gas environment is presented.

Heat-treated 4Kh4N5M4F2 steel with adjustable austenitic transformation during operation was studied. The temperature range (450–500°C) in which the tempering brittleness of this steel was manifested was established. The impact toughness of the samples after different tempering temperatures and after steel hardening from 1100°C was determined and it was shown that after tempering at 475°C the minimum value of the impact toughness at room temperature (15 J cm² ) was reached. The role of Ni as a Fe_1–xNi_x replacement element was analyzed, and the segregation along the grain boundaries of the Me₆C carbide phase in the solid solution, which caused a decrease in the impact toughness and an increase in the steel brittleness, was recorded.

Low-carbon pipe steel’s corrosion rate and hydrogenation in a chloride-acetate solution with CO₂/H₂S mixtures at different temperatures and pressures were investigated. The rate of corrosion and hydrogenation depend on the H₂S concentration and the properties of corrosion films. In a solution with a pressure ratio of ({P}_{{text{CO}}_{2}}:{P}_{{text{H}}_{2}text{S}}=30:1) and at the beginning of exposure at a pressure ratio of 3:1 corrosion slows down due to the formation of Fe_1+xS mackinawite film. Over time, mackinawite transforms into hexagonal FeS troilite with an acicular structure, and the corrosion rate increases in approx. 2 times. The corrosion rate of steel at 60°C and 5 MPa in a solution with a pressure ratio of ({P}_{{text{CO}}_{2}}:{P}_{{text{H}}_{2}text{S}}=30:1) was twice as low as at 20°C and 0.1 MPa. A dense layer of cubic iron sulfide FeS crystals was formed on the surface, which reduces corrosion. The adsorption of hydrogen by the steel reduced in approx. 15 times as the temperature increases.

The TiN coating obtained by vacuum-arc spraying on the surface of commercially pure VT1-0 titanium and thermodiffusion saturation in a nitrogen atmosphere was studied. The coating was evaluated by thickness, phase composition, surface roughness, microhardness, and adhesive strength. Rockwell adhesion tests showed that the TiN coatings applied to both untreated and pre-nitrided titanium meet the HF2 adhesion level accepted for commercial application on products.

The anisotropy of the elastic properties of Inconel 718 alloy produced by 3D printing (selective laser sintering) from powders was studied depending on the direction of 3D printing. The influence of the initial powder mixture and the subsequent heat treatment (post-printing treatment) on the anisotropy of the elastic properties of the alloy was evaluated. It was shown that the proposed treatments can reduce the anisotropy of the elastic properties of the alloy. The results of the theoretical estimation of the elastic and shear moduli, Poisson’s ratio, and their anisotropy in the horizontal and vertical directions of 3D printing are presented, using elastic constants of the single crystal and texture characteristics determined by X-ray diffraction. It is shown that the obtained theoretical values deviate from the corresponding experimental ones by 6–10%. The results of elastic properties and their anisotropy estimating can be used to improve the accuracy of calculating the stress-strain state and optimize the strategy of 3D printing of complex parts made of Inconel 718 alloy.

Methods and samples have been developed and improved for comprehensive evaluation of the operational properties of materials for deposited elements and tools for pressure metal processing. In particular, the method of assessing the wear resistance of deposited metal at room (20°C) and elevated (600°C) temperatures, as well as the thermal resistance of deposited metal was improved. Designs of samples and optimal test modes, which simulate their real operating conditions, were chosen. The introduction of the boron microadditives in the amount of 0.01% leads to an increase in the operational properties of the deposited 25Kh5FMS and 35V9Kh3SF steels in 1.2–1.6 times. According to these results, the composition of the flux cored FCW-Dep-25Kh5FMS and FCW-Dep-35V9Kh3SF wires was improved due to the addition of FMI-2 ligature containing boron.

The characteristics of fatigue failure of the working blades of the first stage of the high-pressure turbine of the power gas-turbine engine were determined. Experimental studies were carried out on blades obtained according to the improved technology from the CM88Y alloy, which is used in the serial production of gas-turbine units. The blades withstood the test base of 1×10⁷ cycles at a stress of 200–240 MPa. The established endurance limit corresponded to the given service life of blades of this type.

Resistance of pipe steels to hydrogen embrittlement is an important indicator of their serviceability. Pipes are manufactured from steels of a wide strength range. With the strength increase, a susceptibility to hydrogen embrittlement in general increases. This regularity is usually true for steels in the as-received state; however, the long-term operation can increase hydrogen susceptibility even of low- strength steels. This is caused by the development of damage dissipated in the metal bulk with the formation of voids due to deformation caused by high-pressure recombined hydrogen in them. Implementation of the hydrogen-induced damage mechanism, associated with the formation of deformation voids, extends the strength range of pipe steels, which become prone to operational hydrogen embrittlement.

The characteristics of the modified layer of commercially pure BT1-0 titanium (c.p. BT1-0 titanium) after oxygen thermal diffusion saturation (oxidation) and subsequent electrospark alloying (ESA) with a graphite electrode were analyzed. The phase composition of surface layers, their hardness and tribological properties were studied. It was shown that both surface electrospark alloying of titanium with a graphite electrode and combined processing (oxidation followed by ESA) improve its tribological characteristics during friction without lubrication. As a result, the friction coefficient decreases from 0.4–0.5 to 0.15–0.17. At the same time, the wear resistance of titanium increases in 1.2–2.9 times.

The influence of the conditions of original components mixing and sintering temperatures on the peculiarities of microstructure formation of the cemented carbide WC + 20 mass% Ni prepared of ultra-coarse-grained (80/40 μm) tungsten carbide particles is investigated. The metallographic analysis shows that for the formation of such hard alloy microstructure, it is sufficient to use liquid phase sintering and preliminary economical wet mixing of WC with Ni powder. The strength under bending and compression is 1530 and 1720 MPa, respectively, the density is 13.51 g/cm³, and the hardness is 76 HRA. For the first time, the compressive stress-compression strain curve for this alloy with an average carbide grain size of 20 μm is experimentally obtained. The alloy plasticity is 6 times higher than that of the alloys prepared under other technological modes.