Powder Metallurgy and Metal Ceramics最新文献

The influence of detonation spraying parameters on the porosity and adhesion of (Ti, Cr)C–Ni coatings was studied. These detonation coatings were applied from (Ti, Cr)C-based composite powders containing 18, 25, and 33 wt.% Ni onto a steel substrate. The particle-size distribution of the powders was –63+40 μm. A Dnipro-5M installation was used for detonation spraying. The flow rate of acetylene and oxygen, the air pressure for ejecting detonation products, and the spraying distance were varied in the spraying process. The structure of the coatings was examined by optical microscopy and electron probe microanalysis. The adhesion of the (Ti, Cr)C–Ni coatings was determined by the pin method, and the porosity was measured by the linear Rosival method. In the detonation spraying of (Ti, Cr)C–Ni composite powders, particles of double titanium–chromium carbide refined to 6–7 μm, contributing to the development of a fine and uniform structure of the detonation coatings. It was found that the detonation spraying parameters should be adjusted upward when the nickel content changed from 18 to 33 wt.% in the (Ti, Cr)C–Ni composite powders. The increase in the nickel content from 18 to 33 wt.% resulted in higher adhesive strength and lower porosity of the coatings. In the research, an acceptable level of adhesive strength and porosity could not be reached for the (Ti, Cr)C–18 wt.% Ni detonation coating. The (Ti, Cr)C–33 wt.% Ni detonation coating exhibited the highest adhesive strength (101 MPa) and the lowest porosity (2%) among the studied coatings and is thus promising for further research of its tribological properties.

The isoperibolic calorimetry method was used to determine the mixing enthalpy of liquid alloys in the Ni–Tb system in the composition range 0 < x_Ni < 0.6 at 1660 ± 1 K. The minimum mixing enthalpy of melts in this system was –41.8 ± 0.9 kJ/mol at x_Ni = 0.6. The activities of components and the mole fractions of associates in these melts were calculated according to the ideal associated solution (IAS) model with our and literature values of formation enthalpies for compounds in the Ni–Tb system and with phase diagram data. Two associates were selected for the calculations: TbNi and TbNi₅. The activities of the components showed large negative deviations from the ideal solution, with the simplest associate, TbNi, being predominant (x_max = 0.65). The second associate was present in a much smaller proportion (x_max = 0.22). These data correlate with the mixing enthalpies of the melts, formed with significant exothermic effects. To assess the reliability of the formation enthalpies of compounds and melts in the Ni–Tb system, they were compared with those of LnNi₅ compounds and liquid alloys in the Ni–Ln system. All were determined with different options of the calorimetry method. Hence, to be compared, they were plotted as a function of the Ln atomic number. Most of the data points aligned with two trend lines, except for the data for compounds in binary Ni–Gd(Dy, Er) systems and melts in binary Ni–Ce (Eu, Yb) systems. Regarding these ΔH_min values, which are more exothermic (Ni–Ce system) and less exothermic (Ni–Eu(Yb) systems) than all others, they may be attributed to the electronic structures of atoms in the components of the melts. The Eu and Yb atoms are known to have half-filled and completely filled 4f orbitals, while the Ce atom contains one electron in the 4f orbital. Therefore, Eu and Yb are divalent and Ce is tetravalent in the nickel alloys. Since nickel is a strong electron acceptor, the energy of its interaction with Ce is greater and that with Eu and Yb is lower compared to other neighboring lanthanides.

This paper considers the dependence of the thermodynamic properties of glass-forming liquid alloys of the (Fe, Co, Ni, Cu)–Ti–Zr systems on composition and temperature. The associate solution model (ASM) was used as a calculation tool. The results of the calculations correspond to the experimental data on the integral mixing enthalpy, presented in the first part of the work, and reveal the regularities of changes in other thermodynamic functions and the features of interaction between components in these liquid alloys. It was established that the excess thermodynamic mixing functions in each system have negative values, which are determined by pair interactions between Fe, Co, Ni, and Cu as electron acceptors and Ti and Zr as electron donors. The trend of changes in the minimum values of excess thermodynamic mixing functions of the systems shows an increase in their absolute values along the 3d-series from iron to nickel and a significant decrease for copper, which corresponds to a change in the acceptor capacity of metals along the transition series. The temperature dependence of the thermodynamic mixing functions consists in an increase in negative deviations from ideality and an increase in the intensity of interaction between components with a decrease in temperature. The formation of glass-forming liquid alloys from pure metals is accompanied by an increase in the thermodynamic stability of the liquid phase, which is reflected in negative values of the Gibbs mixing energy. In the range of 800–1873 K, the Δ_mG function of liquid equiatomic alloys of the systems considered shows values at the level of –20...–35 kJ/mol. Within the framework of ASM, using the total mole fraction of associates as a quantitative estimate of the degree of short-range chemical order, it is shown that liquid alloys of the Me–Ti–Zr system are characterized by significant chemical ordering, which increases with decreasing temperature. Using the empirical rule, the experimentally known compositions of amorphous alloys for the Cu–Ti–Zr and Ni–Ti–Zr systems were interpreted and the composition regions of liquid alloy amorphization were predicted for the Fe–Ti–Zr and Co–Ti–Zr systems.

The furnace infiltration technique was proposed to produce two-layer macroheterogeneous composite coatings. The technique involved consecutive infiltration of hard alloy reinforcement granules with two metallic matrices differing in the melting point. The infiltration resulted in a twolayer composite coating, with the layers being strengthened with the same reinforcement but not having the same matrix compositions. The Fe–12.5% B–0.1% C alloy was used as the reinforcement and the L62 copper-based alloy or hypoeutectic Fe–3.5% B–0.2% C alloy was the matrix. Quantitative metallography, energy-dispersive microanalysis, and microhardness measurements were employed to examine the structurization of interfaces between the boride reinforcement and the molten matrices. Furnace infiltration ensured virtually defect-free structure of the two-layer composite coating, with porosity not exceeding 5 to 7%. This was achieved through the dissolution of reinforcement surface phases in the molten matrices during infiltration without forming brittle intermetallic phases at the interfaces. The intensity of contact interaction processes at the interfaces between iron borides and iron- and copper-based matrices was compared. The mechanical and performance properties of the composite coating layers were studied. The combination of two layers prevented the delamination of the composite coatings under nonuniform distribution of temperatures, stresses, and strains. This determines the prospects of using the proposed technique for surface strengthening of aerospace engineering parts.

An equiatomic NiFeCrWMo high-entropy alloy (HEA) produced by mechanical alloying was used as a binder alternative to cobalt for the manufacture of WC-based hardmetals. The WC–10 HEA (wt.%) powder mixture was homogenized in a planetary-ball mill for 2 h and consolidated by electron beam sintering (EBS) for 4 min at a temperature of 1450°C and spark plasma sintering (SPS) for 10 min at a temperature of 1400°C. The relative density of the sintered samples reached 99.4%. The phase composition, microstructure, and mechanical properties of WC–10 HEA hardmetals were studied by X-ray diffraction, scanning electron microscopy, and microindentation. The effect of the NiFeCrWMo HEA binder on the microstructure and mechanical properties of WC–10 HEA hardmetals in comparison with the conventional VK8 hardmetal (WC–8 Co) was determined. The WC–10 HEA hardmetal consolidated by EBS consisted of WC grains, a NiFeCrWMo HEA binder with a bcc structure, and a small amount (3.5%) of complex carbide (Ni, Fe, Cr)_xW_yC_z, whereas the amount of the complex carbide after SPS increased to 47% due to longer sintering and pressure application. No noticeable growth of WC grains was observed during sintering of the WC–10 HEA hardmetal because of the multielement composition of the NiFeCrWMo HEA binder and the formation of complex carbide (Ni, Fe, Cr)_xW_yC_z layers, preventing the growth of WC grains. The hardness HV and fracture toughness K_Ic of WC–10 HEA hardmetals after EBS were 18.9 GPa and 11.4 MPa · m^1/2 and those after SPS were 19.9 GPa and 10.8 MPa · m^1/2. The hardmetals with a HEA binder exhibit an excellent combination of hardness and fracture toughness. These values are higher than those for the conventional VK8 hardmetal (WC–8 Co) produced by EBS for 4 min at 1350°C, whose hardness is 16.5 GPa and fracture toughness K_Ic is 9.5 MPa · m^1/2.

The paper presents a theoretical evaluation of the mechanical properties of porous materials with an inverse opal structure, which is important for their application in various technological fields. The study focuses on a porous nickel-based material produced by a sequential multistep process that includes the self-assembly of polystyrene spheres, sintering, electrolytic deposition, and subsequent removal of polystyrene to achieve the desired structure. The study covers the process of transition from elastic to irreversible deformation. The objective of this study is to apply the finite element method to model the transition process to reveal the relationship between the structural characteristics of materials, such as porosity and coating thickness, and their mechanical properties. The yield surface was constructed by computational modeling on a representative cell with a number of points in the (p, τ) plane for two cases of opal structure: a highly porous uncoated structure and a structure with an additional solid phase layer. One of the results included approximation of the yield surface with a phenomenological Deshpande–Fleck crushable foam model available in finite element modeling packages. The conclusions show that the effective plastic properties of materials with an inverse opal structure significantly depend on their porosity level and the presence of additional coatings. The yield curve plotted for a porosity of 0.9 is close to the associated plastic flow law, allowing the material’s behavior under loading to be assessed from the uniaxial stress state. However, for a structure with medium porosity and an additional coating layer, the surface becomes significantly unassociated, with a discrepancy of almost 30%. The application of the Deshpande–Fleck model for crushable foam in the approximation of the numerical data from the study demonstrates its relevance in describing the plastic behavior of this structure only at high porosity values.

The influence of pore structure evolution in compacts sintered from nickel carbonyl powder with an average particle size of 1.4 μm in the temperature range 200–1000°C on local and bulk shrinkage was analyzed. The pore structure of the samples was characterized by the maximum and average diameters of pore channel constrictions determined by the Barus–Bechhold method. To minimize local (incoherent) shrinkage in the sintering of fine nickel powders, a criterion for pore structure homogeneity in compacts, α ≤ 0.03, was selected. The criterion was determined by the difference between the maximum and average diameters of pore channel constrictions. The influence of pore structure evolution on local and bulk shrinkage during sintering of compacts produced from nickel carbonyl powder with an average particle size of 1.4 and 4 μm was experimentally confirmed. The local shrinkage was due to the three-level structure and wide particle size distribution of the nickel carbonyl powders. A method was proposed to determine the average diameter of particles (agglomerates) in nickel carbonyl powders using the Kozeny equation, establishing a relationship between the particle diameter, the maximum diameter of pore channel constrictions, and the porosity of the compacts, varying from 0.25 to 0.45.

A Discrete Element Method (DEM) was applied to establish a model that simulates a cross-shaped powder system under hot compaction. The average stress, force chains, principal stress angles, and coordination numbers were recorded and studied. The experimental results show that the stresses in the vertical part of the cross-shaped powder system are higher than in the lateral part, and the highest stress value is always concentrated in the upper zone of the system. This is also consistent with the strength of the force chains in the vertical part being stronger than that in the lateral part. The angle of the principal stress is consistent with the direction of the external load and shows anisotropy and irregular distribution during the compaction process. The vertical section of the cross-shaped powder system tends to be 90°, except for the area close to the lateral section, which tends to be 70°. However, the principal stress angle of the lateral part tends to be 0° during the compaction process. The coordination numbers of the measurement circles have a series of sudden changes and increase with the pressing, the changes of which correspond to the stress distribution.

As the aerospace industry continues to grow, so does the demand for new materials that can withstand high temperatures and corrosive environments. In this paper, materials from the Ti–Al–C system that thrives in the aforementioned environments are studied. The method of measuring the grain size was described according to the relevant standards. The geometrical parameters of titanium carbide and its volume fraction have been determined under the ASTM E112 and ASTM E562 standards, respectively, for two series of specimens that were produced with different parameters and methods. The grain sizes determined are G12 and G12.5 according to ASTM E112. The volume fractions determined for the two series of samples are 20.22 and 17.65%, respectively. Using the above parameters, elastic and shear modulus, and Poisson’s ratio were determined for the specimens tested using RVE modeling. RVE results showed that materials with higher volume fractions and larger average grain size resulted in stiffer materials. Specimens with higher TiC content exhibited higher elastic and shear modules, which were 153.6 and 58.3 GPa, respectively. Poisson’s ratio was the lowest at 0.315. However, the difference was not significant between the specimens, the elasticity and shear modulus, of a specimen with a lower concentration of TiC, are 145 and 55.2 GPa, respectively. Poisson’s ratio was higher and equal to 0.319. Comparing the above properties with the popular aerospace alloy Ti–6Al–4V, both specimens are much stiffer.

Changes in the dielectric properties of two-dimensional (2D) microsized molybdenum disulfide powders in response to ambient air humidity at room temperature were studied (impedance spectroscopy, 1 Hz–20 MHz). The microsized 2H-MoS₂ powders were found to absorb significant amounts of moisture (0.43–2.88 wt.%, 3.5 h, relative air humidity of 45–100%). According to impedance spectroscopy data, reversible water intercalation/deintercalation processes led to significant changes in the dielectric properties (total, active, and reactive (capacitive) resistance, capacitance, loss tangent, and real component of relative permittivity) of 2H-MoS₂ powders until equilibrium was reached. In equilibrium, the dielectric properties depended on humidity and frequencies. The dielectric properties of microsized 2H-MoS₂ powders are dynamic functional characteristics that can be effectively controlled over wide ranges by varying the humidity and frequency levels. It is assumed that changes in the dielectric properties of microsized 2H-MoS₂ powders are due to the formation of 2D nanosized MoO_3–x/MoO₃/H⁺_x(H₂O)_yMoS₂ heterostructures on the surface of the intercalated H⁺_x(H₂O)_yMoS₂ phase particles. These findings can be used to improve nanotechnologies that use aqueous environments, optimize the semiconductor, tribological, and catalytic properties of 2H-MoS₂, and develop multifunctional 2D nanomaterials (humidity sensors, sorbents, and photocatalysts for water purification and electro(photo)catalysts for hydrogen production by water electrolysis).