Russian Metallurgy (Metally)最新文献

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.

Abstract—The influence of combined thermochemical treatment consisting of preliminary vacuum nitriding, subsequent vacuum carbonitriding, and final heat treatment (quenching from repeated heating + subzero treatment at –78°C + low tempering) on the wear resistance of high-chromium martensitic bearing steels (95Kh18-Sh, 110Kh18M-ShD) is studied. The combined treatment is shown to increase the contact fatigue limit to 4900 MPa at a specific wear rate no more than (1.05–1.29) ×10^–5 mm³/(N m). Preliminary nitriding is found to positively affect wear resistance and fatigue limit, and subzero treatment negatively affects these characteristics.

The structure and tribological characteristics of 1-μm-thick TiAlN-based coatings with soft metal additions (In, Sn, Pb), which are prepared by reactive magnetron sputtering of separated cathodes, are studied. The coatings are found to have a columnar nanocrystalline composite structure. The Al_xTi_{1 – x}N, In(Sn) solid solution, Pb, and PbO phases are found in the coatings. The microhardness of the coatings is 280–382 HV. Under reciprocating motion conditions at room temperature, the minimum friction coefficient (μ ≈ 0.20) and high stability of tribological characteristics are achieved for a TiAlN–InSn coating with the atomic ratio Al/(Al + Ti) = 0.53. As the test temperature increases to 100 or 200°C, the wear of the coating and the transfer of the counterbody material decrease; which is related to the presence of the Al_xTi_1–xN phase with a wurtzite structure characterized by a low shear strength.

Abstract—The influence of an impact on the mechanical behavior of a carbon fiber reinforced polymer is investigated using interlaminar shear tests of a short beam with a simultaneous registration of acoustic emission signals. Displacement and deformation fields detected by digital image correlation have also been studied. The influence of the preliminary impact energy on the change in damage mechanisms is revealed, and deformation localization in the material is detected.

Abstract—The effect of the temperature of preliminary annealing (420 or 300°C, 1 h) and the number of roll leveling machine passes (one to three) on the microstructure and mechanical properties of aluminum VD1 (Al–Cu–Mg) thin sheets (3-mm thick) is studied. Alternating bending deformation by one- and two- pass rolling monotonically increases the yield strength of the annealed (at 420°C) alloy from 99 to 133 MPa (by 34.8% relative to its annealed state) without changing the strip geometry and its ductility. Annealing at 300°C increases the yield strength to 300 MPa but reduces ductility. Subsequent alternating bending does not change the mechanical properties of the alloy.

Abstract—The thermal stability of the Al–4 wt % Cu–3 wt % Mn experimental alloy at temperatures to 400°C and its standard mechanical properties and microhardness are studied. The alloy composition is chosen so that more than 10 vol % fine Al₂₀Cu₂Mn₃ particles are formed in it. The alloy is prepared by electromagnetic casting followed by working, which includes upsetting and subsequent high-pressure torsion (HPT). HPT is found to result in an almost threefold increase in the hardness as compared to that of the cast ingot (250 and 90 HV, respectively). The strength of the alloy subjected to HPT increases by 1.2 to 1.4 and 1.6 to 1.8 times as compared to that observed after upsetting at 20 and 400°C, respectively. The strain hardening is found to be retained after annealing at up to 250°C for 5 h; in this case, plasticity increases substantially.

Abstract—The possibility to control the structure formation in a VT22 titanium alloy of the transition class (Ti–5.5Al–4.3V–4.2Mo–0.8Cr–0.8Fe) using thermohydrogen treatment (reversible hydrogen alloying) is studied. A high volume fraction of the β phase, which is characteristic of α + β titanium alloys of the transition class (at least 40% in the alloy under study), is shown to suppress martensitic transformation even at 0.1 wt % hydrogen; at 0.3 wt % hydrogen, only the metastable β phase is retained in the structure of the alloy. Different types of structure, from a bimodal to a fine equilibrium structure, can be formed in the alloy during subsequent vacuum annealing by controlling the development of the β → α transformation. A fine α + β structure with an α-phase particle size of at most 0.5 μm forms only upon low-temperature (625–700°C) vacuum annealing.

The structure and properties of titanium/aluminum–magnesium alloy explosive welds and the influence of the magnesium content on the weld strength are studied. The welded joints of VT1-0 titanium with AMg5 and AMg6 alloys are found to fail during both welding and the application of an external load along the near-boundary zone of an aluminum alloy, and the fracture is brittle. This fracture is shown to be due to the formation of a thin aluminum alloy interlayer with a refined structure consisting of equiaxial grains less than 1 μm in size at the joint boundary, and the boundary of this structure with the base metal is a stress concentrator.

Using the finite-element method, the problem of thermoelastic stress distribution in a high-speed R2M9 steel coating on a 30KhGSA steel substrate has been solved. Stress distributions in the coating versus distance from the surface have been obtained. It has been found that normal component σ_yy of the stress tensor varies nonmonotonically along the rounding radius and monotonically along the central axis. It has also been shown that the von Mises stress intensity rises toward the coating boundary, as a result of which a minimum appears in the dependence of the microhardness on distance to the coating boundary. Stability analysis of carbide phase inclusions subjected to thermoelastic stresses has been carried out. It has turned out that inclusions 10 μm or greater in size are unstable if their thickness is about 1 μm or less.