Russian Metallurgy (Metally)最新文献

The structure and properties of filler rods made of a B83 alloy reinforced with Al–Bi or Ti₂NbAl intermetallic particles less than 100 μm in size in an amount of 3 wt % are studied. The rods are extruded from powder compositions and are intended for the deposition of antifriction coatings. Reinforcement is shown to increase the homogeneity of the grain structure of the B83 matrix alloy and promotes its refining: 66 and 68% of SnSb intermetallic crystals have a surface area of 2000–5000 μm² in the case of reinforcement with Al–Bi and Ti₂NbAl particles, respectively, and 33% of the SnSb crystals in the matrix alloy have a surface area exceeding 5000 μm². The filler materials made of the developed powder compositions are superior to the B83 cast alloy in the fluidity parameters and tribotechnical properties. The best fluidity indicators of the weld pool and the lowest friction coefficient are achieved using Ti₂NbAl-containing filler rods.

The effect of temperature and time parameters and sintering conditions on the structure and properties of porous VT1-0 titanium samples fabricated by cold pressing of rapidly quenched fibers is studied. The samples are sintered at 750–850°C for 1.5–2 h in a vacuum and upon hydrogenation to a hydrogen concentration of 2.5 wt % and subsequent dehydrogenation. The hydrogenation allows us to fulfill the sintering of fibers in a temperature range corresponding to the β-Ti + TiH₂ phase region, and the nonhydrogenated fiber is sintered at the same temperatures corresponding to the α-Ti region. The hydrogenation–dehydrogenation in the course of sintering is found to exclude the imperfection of joint zones and to increase the mechanical properties of the porous sintered material. The maximum reached proportionality limit of the material subjected to hydrogen and vacuum sintering is 108 and 71 MPa, respectively.

Abstract—The mechanical and functional properties of a composite material consisting of a polyethylene matrix reinforced with a titanium nickelide wire are investigated. This composite material has a high fracture strength under static and cyclic bending. The effective ultimate strength of the composite material during interlaminar shear exceeds 3.6 MPa. Depending on the structural state of titanium nickelide, the fatigue life of the composite material is 2–50 times longer than that after similar reinforcement with a corrosion-resistant steel wire. The viscoelastic behavior of polyethylene is found to affect the superelasticity and the one-way shape memory effect of the composite material. Despite the low adhesive strength of the polyethylene/titanium nickelide interface, this composite material can exhibit the one-way shape memory effect with a shape recovery η ≈ 0.95.

Abstract—The structure, hardness, and ductile–brittle transition temperature (DBTT determined on small Charpy specimens) of the heat-affected zone (HAZ) of two standard welded joints of a VVER reactor vessel made of 15Kh2NMFA-A steel with different nickel contents (1.34 and 1.46 wt %) are studied. Two (high- and low-hardness) subzones are distinguished in the HAZ. The DBTT of the high-hardness subzone is shown to be 60–70°C lower than that of the base metal, which is caused by the formation of martensite and lower bainite structures and grain refinement. The DBTT of the low-hardness subzone is 20–30°C lower than that of the base metal, which is explained by a lower density of carbides in this zone.

The structure and microhardness of an austenitic steel coating plasma sprayed onto a cylindrical surface are studied after friction stir processing (FSP) with two steel tools at a pressure of 30 MPa. During FSP, the coating temperature is found to increase to 1235°C, which makes it possible to plastically deform the coating and to compact it by destroying the initial structure and welding sprayed particles. As a result of FSP, the microhardness of the coating increases from 3.2 to 4.6 GPa.

Abstract—The compressive properties of titanium having various degrees of porosity fabricated by powder metallurgy methods from a powder mixture of titanium hydride TiH₂ and a pore forming agent (ammonium bicarbonate NH₄HCO₃) are studied. Sintering is performed in vacuum or argon at 1150 and 1200°C. A change in the volume fraction of ammonium bicarbonate from 0 to 60% is shown to control the porosity of titanium samples from 3 to 59%. The compressive elastic modulus of porous titanium is found to decrease from 50 to 4 GPa when the porosity increases from 3 to 59%. The sintering atmosphere and a change in the sintering temperature by 50°C are shown to insignificantly affect the elastic modulus: it changes by ≈10%.

Abstract—The causes of the technological brittleness of multicomponent copper–zinc alloys are investigated using complex LMtsAZhN brass (Zn–Cu–Mn–Al–Fe–Si–Ni) as an example. The relation of cracking of brasses to silicide-forming elements and lead is shown. The distribution and morphology of lead precipitates in destroyed blanks have been studied. The formation of metastable precipitates is shown to be caused by the redistribution of copper, aluminum, silicon, and phosphorus. The stoichiometry of silicides of various morphologies in the industrial batches of brass blanks is determined. The conditions for eliminating the technological brittleness of complex copper–zinc alloys are formulated.

Abstract—The axial and annular tensile strengths of experimental SiC/SiC composite fuel rod cladding tubes with a thin-walled (325 μm thick) liner made of an E110 zirconium alloy have been studied. The strength of the tubes is 216 and 1189 MPa during axial and annular tension, respectively.

Fibers are fabricated from a Co₆₉Fe₄Cr₄Si₁₂B₁₁ alloy glass covered amorphous microwire. They have two types of sizes: the diameter is D = 17 and 50 μm and the length is 7 and 15 mm, respectively. The influence of their geometric parameters and concentration (0.5–3%) and the method of introduction on the mobility, the average density, and the bending and compressive strengths of cement systems (mortars) has been studied. The bending strength of the cement system is found to increase by 54% in the case of its reinforcement with amorphous glass–metal fibers of diameter D = 17 μm in an amount of 0.5% of the Portland cement weight and by 22% in the case of reinforcement with fiber of diameter D = 50 μm in an amount of 1%. The compressive strength changes insignificantly herewith. The introduction of fibers increases the crack resistance coefficient of the cement systems under study from 0.098 to 0.116–0.164.

The electrical conductivity of LiF–KF–NaF (FLiNaK) molten system was measured in the temperature range 480–777°C. The comparison of the obtained experimental data on molten FLiNaK with the available data for individual, double and ternary fluoride melts containing KF, NaF and LiF was carried out. The resulting dependence of electrical conductivity on molar volume of the system demonstrates that at 867°C and V_m larger than 23 cm³/mol the specific electrical conductivity is practically independent on molar volume and respectively on the molten mixture composition. The electrical conductivity of FLiNaK–CeF₃ molten systems with the cerium fluoride additions ranging from 0 to 25 mol % was measured depending on both the temperature and concentration of CeF₃. In addition, the electrical conductivity of 0.85 FLiNaK–0.15CeF₃–Li₂O molten system with Li₂O additions up to 2.3 mol % was measured. The investigation demonstrates that the addition of cerium fluoride and oxide results in a decrease of the electrical conductivity of the fluoride molten system.