Russian Metallurgy (Metally)最新文献

The effect of the surface state of 316L steel samples, which were obtained by selective laser melting, on the mechanical characteristics, stages and fracture mechanisms, acoustic emission parameters, and the strain-state characteristics, which were estimated by the digital image correlation method, has been studied. A decrease in the static and fatigue strength of as-built samples in the region of low loading amplitudes and an increase in the elongation at fracture have been revealed compared to these characteristics for machined samples. For as-built samples, the appearance of high-amplitude acoustic emission signals indicating the nucleation of surface microcracks at an earlier deformation stage has been detected. It is assumed that knee point on the fatigue curves and amplitude dependences of the characteristic zones size at fracture surfaces are associated with the transition from a plane stress state to a plane strain state of the material with a decrease in the stress amplitude.

Abstract—An empirical mathematical model for the dynamics of friction force changes is used to analyze the tribological properties of lubricating compositions based on TSp-10 transmission oil containing C = 1–4 wt % Mg₆[Si₄O₁₀](OH)₈ serpentinite microparticles. The minimum friction force (13% lower than that of the base lubricant) is achieved at a serpentinite content of 2.1 wt %, and the minimum wear (46% lower than that of the base lubricant) is achieved at 2.6 wt %. An analysis of the dependence of the wear crater diameter on the serpentinite concentration using the Hertz theory made it possible to establish the ranges of serpentinite concentrations at which oxidative wear or seizure occurs. Seizure of the rubbing surfaces is possible at a serpentinite content C = 0–0.9 wt % and C > 4.35 wt %. At C = 0.9–4.35 wt %, a lubricant layer retains its load-bearing capacity.

Abstract—The plastic properties of specimens made from an Al–2.3% V alloy and A85 aluminum produced by selective laser melting have been investigated. Fracture loci for these materials are constructed. The ultimate plasticity of the materials significantly is found to depend on the deformation conditions (type of stress state characterized by Lode–Nadai coefficient μ_σ). Under tensile and shear testing conditions (–1 ≤ μ_σ ≤ 0), the ultimate plasticity of the materials is almost the same. In the case of testing by extrusion of the bottom of a thick-walled cup (μ_σ = +1), the ultimate plasticity of the Al–2.3% V alloy is approximately twice as high as that of the initial aluminum under tensile stress conditions and 30% higher under compressive stress conditions.

The isometricity coefficients of abrasive powder grain fractions of black silicon carbide of grit sizes F180–F22 are calculated; the powders are produced by roll pressing and jet milling followed by sieving on sieve screens. The distribution law of the isometricity coefficient is established. The degrees and directions of correlations and the reliability coefficients of approximation of linear dependences between the isometricity coefficient and the parameters determining it are determined.

Abstract—The structural-simulation model developed for the deformation for shape memory alloys has been extended to account for the martensitic inelasticity effects. This model successfully explains the qualitative and quantitative differences between the strain accumulation diagrams for direct transformation and martensitic inelasticity.

The relationship by mass between phase transformations upon heating and cooling of Ti–55.6% Ni alloy in a state aged in various modes with its shape change during the implementation of a one-way shape memory effect has been studied. It is shown that shape restoration occurs in two stages after deformation at –10°C with 2% bending, In this case, one stage is characterized by a small (0.3–0.4%) restored deformation and the other stage by a large deformation value (1.0–1.1%). A small part of the deformation (0.3–0.4%) is eliminated at the low-temperature stage of shape restoration after two hours of aging at 520°C and two-stage processing at 520 + 460°C and at the high-temperature stage after aging at 460°C. X-ray diffraction tests showed that the duration of the first and second stages of shape change depended on the sequence of occurrence and/or the superposition of R → B2, B19' → R and B19' → B2 transformations during heating.

Abstract—The chemical and phase compositions, structure and mechanical properties of an alloy based on the NiAl—Cr—Co system (base–2.5Mo–1.5Re–1.5Ta–0.2Ti) obtained by centrifugal SHS casting in a pilot industrial plant have been studied. The results of the study were analyzed in comparison with similar parameters for an alloy of the same composition, but synthesized in a laboratory SHS plant and having a smaller mass of 0.8 ± 0.1 kg as compared to the mass of a large-sized ingot of 4.7 ± 0.1 kg. The large-sized ingot with chemical and phase compositions uniform by volume is reported to have been produced, its metal demonstrating similar kinetics and heat resistance at 1150°C (30 h) at different distances from the center. It was found that the heat resistance of the alloy decreased with ingot mass increasing from 55 ± 3 g/m² for the laboratory ingot to 19 ± 3 g/m² for the large ingot. The strength properties of the metal of the large ingot during compression testing were (sigma _{{text{u}}}^{{text{c}}}) = 1662 ± 10 MPa, (sigma _{{0.2}}^{{text{c}}}) = 1531 ± 25 MPa and during tensile testing σ_u = 293 ± 10 MPa, σ_0.2 = 236 ± 5 MPa, which was practically no different from the properties of the laboratory ingot. The mechanical properties of NiA–Cr–Co-based alloys of various alloying systems synthesized by the SHS method with subsequent use of special metallurgy methods are also given.

The effect of high-pressure torsion (HPT) and subsequent annealing on the microstructure, mechanical properties, and temperature stability of an aluminum alloy, the composition of which includes 92.1 wt % Al, 4.6 wt % Mg, 1.3 wt % Ca, 0.8 wt % Mn, 0.3 wt % Fe, 0.2 wt % Zr, and 0.2 wt % Si, is studied. HPT is performed at room temperature; post-deformation annealing is conducted at 100–400°C. HPT is found to result in threefold hardening, which remains unchanged up to 200°C. The high plastic deformations reached during HPT lead to the formation of nano- and submicrocrystalline grain–subgrain microstructure characterized by a high level of internal stresses. The best combination of a high strength (655 MPa) and adequate plasticity (relative elongation is 2%) is reached after HPT at a small number of revolutions. Post-deformation annealing at 350°C ensures the maximum relative elongation to failure (16%) at a flow stress of ~370 MPa in the absence of strain hardening.

Abstract—The hydrogen embrittlement of Fe₂₀Mn₂₀Cr₂₀Ni₂₀Co_20–xN_x alloys (x = 0.8, 1.4 at %) with disperse Cr₂N particles is studied. The formation of grain-boundary nitrides is shown to favor a decrease in the hydrogen embrittlement index, unlike a fine-grained structure with homogeneously distributed particles. The influence of the interfaces formed during precipitation hardening of the alloys on the fracture micromechanisms in the hydrogen-induced brittle surface zone is described.

Abstract—The structure and mechanical properties (under static and fatigue loading) of Al–6.7Mg–0.3Sc–0.25Zr alloy samples synthesized by selective laser melting (SLM) horizontally and vertically relative to a build platform and subsequently aged at 360°C for 5 h are studied. The density of the synthesized samples is found to be maximal (99.88%) at a laser power of 800 W and a scanning speed of 1500 mm/s. The mechanical properties of such samples are almost independent of the build direction and are as follows: the ultimate tensile strength is σ_u = 420–430  MPa; the relative elongation, δ = 5–8%; and the fatigue limit, σ_R = 130–140  MPa.