Powder Metallurgy and Metal Ceramics最新文献

Herein, novel Ti–TiC(W) composite foams were designed to address the low wear resistance of porous Ti-based alloys. Inexpensive TiH₂ was used instead of Ti powder, and the Ti–10 vol.% TiC matrix was doped with 1 vol.% nanoscale W powder, using 40 vol.% NaCl as the spacer. Ti–TiC(W) composite foams were fabricated through spark plasma sintering, dissolution, and post-heat treatment (PHT) at 900 and 1200°C for 1 h. The influence of W doping on the microstructure and tribological properties of the composite foams before and after PHT was investigated. After posttreatment, the material matrix relative density exceeded 0.9686, with a maximum microhardness of 582.36 HV_0.2 at a PHT temperature of 1200°C. After PHT at 900°C, the W particles gradually diffused into the Ti matrix, forming a diffusion zone. However, some W particles remained undissolved at the center of the diffusion zone, forming a Ti–W corona. After PHT at 1200°C, W formed a uniform mesh structure in the matrix, significantly enhancing the density and microhardness of the matrix by strengthening the strength of precipitation. The coefficients of friction of the materials ranged from 0.1565 to 0.2234, with mild wear observed after PHT at 1200°C and a minimum wear rate of 0.27 ∙ 10^–12 m³· N^–1 ∙ m^–1. The network precipitated phasesynergized to inhibit the formation of wear marks, significantly improving wear resistance. This strategy can enhance the wear resistance of porous Ti-based materials.

Hot forging of a porous billet in a semi-closed die with a double-sided conical flash gutter was modeled using the finite element method with the DEFORM 2D/3D software package. Analysis of the modeling results identified three consecutive stages of the process, driven by variations in the stress–strain state of the forged workpiece. A significant uneven distribution of axial and radial strains over the workpiece cross-section was established at different stages of the process. At the initial stage, the density distribution over the forged material was characterized by significantly higher values in the central region of the forged workpiece compared to the peripheral areas. However, after the die cavity was filled, the material density averaged over the workpiece cross- section. At the final forging stage, the entire volume of the forged workpiece was compacted to an almost nonporous state. This indicated that the axial component significantly influenced the compaction process at the initial and intermediate forging stages. Nevertheless, after the die cavity was filled, intense flow was observed predominantly in the radial direction, and therefore the radial strain component directly influenced the compaction process. The effective stress distribution, closely correlating with the relative density distribution over the workpiece cross-section at the initial and intermediate forging stages, changed after the die cavity was filled and the excess material was extruded into the flash gutter.

The structure and mechanical properties of Al–AlB₁₂ powder composites were studied. Composites containing 2.5, 5, 10, and 15 vol.% α-AlB₁₂ particles in an aluminum matrix were produced by heating and melting a mixture of Al and α-AlB₁₂ powders using a high-frequency heating unit in an inert atmosphere at 1250–1500°C. The melt temperature was increased with higher α-AlB₁₂ content to maintain the required melt fluidity. Aluminum powder with an average particle size of 40 μm and α-AlB₁₂ powder with an average particle size of 2.5 μm were used to produce the composites. The structure was analyzed with X-ray diffraction and scanning electron microscopy. The mechanical properties were determined through compression testing. X-ray diffraction and metallographic analyses revealed that all composites represented an aluminum matrix reinforced with finely dispersed α-AlB₁₂ particles. Metallographic analysis demonstrated uniform distribution of strengthening α-AlB₁₂ particles in the aluminum matrix at 2.5–5 vol.% content. Inhomogeneous particle distribution, with the formation of α-AlB₁₂ agglomerates, was observed at 10 and 15 vol.% α-AlB₁₂. In the composites with 2.5, 5, and 10 vol.% α-AlB₁₂, the integral hardness ranged from 510 to 570 MPa. The hardness of the Al–15 vol.% AlB12 composite was 540 MPa. Mechanical tests of the composites with 2.5 and 5 vol.% α-AlB₁₂ phase revealed their precipitation strengthening, which was well described by a modified Orowan equation. In the composite with 10 vol.% α-AlB₁₂ particles and above, the strengthening effect was diminished, and even softening occurred in the composite with 15 vol.% α-AlB₁₂ particles. This was attributed to the formation of a large number of α-AlB₁₂ particle agglomerates. The minimum content of α-AlB₁₂ particles promoting the precipitation strengthening in Al–AlB₁₂ composites was estimated. Considering the calculation error, it was 1 vol.%.

Two samples of the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy were prepared using argon-arc melting. The samples differed in weight, resulting in distinct cooling modes, and their quantitative phase composition was determined with X-ray diffraction. The electrochemical properties of the alloy samples and the associated composite with a copper addition (in a 1 : 1 alloy-to-copper weight ratio) were studied in both potentiodynamic and galvanostatic modes in the cathodic and anodic potential regions. In particular, the hydrogen capacity and corrosion resistance of the samples discharged to a voltage of 0.7 V relative to the Ni(OH)₂ electrode (~0.4 V relative to the Hg/HgO electrode) were evaluated. In discharge to 0.7 V, the activation of the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy electrodes accelerated as compared to 0.8 V and thus the discharge capacity in the first hydrogenation–dehydrogenation cycles increased significantly, while the maximum achieved discharge capacity of the composite depended on the number of Laves phases in the alloy. At 20°C, the composite produced from the alloy with higher Laves phase content (~90 vol.% C₁₄₊₁₅) activated three to four cycles sooner than the sample with a lower Laves phase content (~80 vol.% C₁₄₊₁₅) and achieved a higher discharge capacity of ~290 mA· h/g when discharged to 0.8 V. The discharge capacity of the composite discharged to 0.7 V relative to the Ni(OH)₂ electrode (~0.4 V relative to the Hg/HgO electrode) combined the contribution from the alloy via electrochemical hydrogenation–dehydrogenation processes and the contribution from copper via oxidation with anodic polarization. The passivation region on the corrosion curve over a wide range from the stationary potential to E = +0.5 V for the alloy section processed in 30% KOH solution demonstrated the corrosion resistance of the alloy electrodes at a discharge voltage of –0.7 V, indicating the absence of selective dissolution of alloy components.

The effect of sintering-activating Y₂O₃ and SiO₂–Y₂O₃ additives on the mechanical and dielectric properties of Si₃N₄ and Si₃N₄–BN ceramics consolidated by spark plasma sintering was examined. The heating rate and applied pressure were maintained at 50°C/min and 35 MPa, respectively. The holding time at a sintering temperature of 1800°C varied depending on the composition of the oxide additives. The Si₃N₄–BN ceramics with Y₂O₃–SiO₂ additives exhibited a 30% reduction in mechanical properties (hardness and fracture toughness) compared to Si₃N₄–Y₂O₃ or Si₃N₄–Y₂O₃–SiO₂ ceramics. The Si₃N₄ ceramics demonstrated resistance to deformation at temperatures ranging from 20 to 900°C. Specifically, Si₃N₄ ceramics with Y₂O₃ or Y₂O₃–SiO₂ additives showed average strengths of approximately 950 and 820 MPa, whereas Si₃N₄–BN ceramics demonstrated a strength of 490 MPa. An increase in temperature from 1000 to 1400°C for all ceramics studied resulted in a gradual decrease in bending strength to approximately 200 MPa. The strength at room and elevated temperatures, Vickers hardness of approximately 4 GPa and 15.5 GPa, and fracture toughness of about 7.7 MPa · m^1/2 meet the current requirements for this type of ceramics. Radiofrequency measurements showed that dense Si₃N₄-based ceramics had a dielectric constant of 8. When 10 wt.% BN was added, the dielectric constant of the composite decreased by approximately 8%. Additionally, residual porosity of about 10% further decreased the dielectric constant of the Si₃N₄–BN composite by around 13% (ε ~ 6.3). This reduction in the dielectric constant had a positive effect on radio transparency. The dielectric loss tangent of the test ceramics did not exceed 2 · 10^–3.

The thermokinetics of recrystallization and interaction processes in the heating of porous compacts produced from a mixture of ultrapure aluminum and iron in a 20 : 80 ratio after cold pressing in a steel die was studied using direct thermal analysis. Recrystallization of the aluminum component and relaxation of the iron component were observed in the temperature range 170–265°C. The iron relaxation and recrystallization exhibited a wavelike behavior. The iron component recrystallized completely in the temperature range 500–700°C. The interaction between aluminum and iron initiated with a reduction reaction through a small amount of surface iron oxides. The reduction of surface iron oxides, involving insignificant heat release, occurred in two stages, reflecting the existence of several iron oxides. Active interaction commenced at the melting point of aluminum. A cascade of exothermic effects, attributed to the interaction of intermetallic compounds with lower stoichiometries, was revealed. In this case, temperature exceeded the existence of the intermetallics, leading to their decomposition and subsequent cooling through the endothermic effect. The cooling rate during the decomposition of intermetallics closely resembled the rate of reaction synthesis. When the nonequilibrium solid solution cooled within the temperature range 500–600°C, the ironbased solid solution decomposed and the intermetallic compound synthesized. Thermokinetic oscillations emerge and gradually subside. At all stages of transitions from stationary states to temperature surges or drops, thermokinetic oscillations with varying frequencies and amplitudes were observed.

90W–7Ni–3Fe refractory alloy with high density and excellent corrosion resistance was obtained for the first time by hot oscillating pressure (HOP) under different oscillating amplitudes (5, 10, and 15 MPa) at low temperatures (1000°C). As the amplitude increased, the 15 MPa sintered sample reached the maximum density of 99.4% with an average grain size of 3.41 μm by min-grain growth rate (about two-thirds of 5 MPa sintered sample), and the max-Vickers hardness reached 462.3 HV_0.5. The sintering curve was changed gently and presented full density at the end of the isothermal holding period. More importantly, the corrosion current density i_corr was reduced by nearly 1.07 times, and the corrosion resistance of 15 MPa samples was better than that of 5 MPa and 10 MPa samples and similar materials ever reported. The results show that the increase of amplitude is beneficial to the densification of refractory tungsten alloy and has a positive effect on improving the density, hardness, corrosion resistance and inhibiting the growth of grain size (the retention of the fine-grained microstructure) at low temperatures.

In this study, forming limit diagrams (FLDs), fracture toughness (FT), and mechanical, magnetic, and electro-physical properties of Al/Fe₂O₃ composites have been investigated experimentally. Accumulative roll bonding (ARB) was used to manufacture composite samples. Then, Al/Fe₂O₃ composites were produced at 300°C for up to eight ARB passes. Also, magnetic composites have been fabricated with 0, 5, and 10 wt.% of Fe₂O₃ particles. The interlayer bonding quality was improved at higher passes. By studying the SEM rapture morphology, it was shown that the rapture mode changed to shear ductile for samples with more passes. For composite samples fabricated at higher passes and compared to annealed samples, elongated dimples were turned into shallow ones. FLDs area as the main forming criterion dropped severely after passing one and then began to improve at higher passes. The fracture test results showed that after the 8^th pass, the value of FT gradually enhanced to the maximum value of 34.3 MPa ⋅ m^1/2. It is also shown that the distribution of Fe₂O₃ particles in the aluminum matrix becomes more and more homogeneous with an increase in the number of rolling cycles, significantly affecting the uniformity of the magnetic capacity. The hysteresis curves improve after more passes due to the higher Fe₂O₃ content, indicating increased coercive force H_c and residual magnetization M_R.

The first part of this review addresses mechanical, physical, and some chemical methods (thermal decomposition, dynamic method, solution combustion synthesis, and sonochemical synthesis) for producing nanocrystalline and fine-grained ZrO₂-based powders. Mechanical methods (high-energy grinding in planetary and ball mills in dry and liquid environments) are used in the synthesis of ZrO₂ powders and analysis of ZrO₂ phase transformations, in the hydrothermal synthesis of ZrO₂ powders in acidic and alkaline environments, and for the deagglomeration of powders produced by other methods. Physical methods (plasma processing, reactive magnetron sputtering, and chemical vapor deposition) are employed when the requirements for powders are prioritized over production costs. They are used in the development of catalysts, sorbents, and coatings. Chemical methods provide control over the formation of primary particles with specific morphology, size, and surface area. Thermal decomposition produces primary particles shaped as spheres, nanorods, and hollow ZrO₂ microspheres with customizable shell structures. Dynamic methods, involving the detonation of high-energy materials or explosives, are promising for the synthesis of nanosized ceramic oxide powders with narrow particle size distributions. Solution combustion synthesis is based on the propagation of self-sustaining exothermic reactions in aqueous or sol–gel environments. Sonochemical synthesis relies on acoustic cavitation. The synthesized powders are applied in the design of photocatalysts, optical materials, forensic materials for fingerprint detection, sensors, biological markers, etc. There is no universal synthesis method that would meet the diverse requirements for all ZrO₂-based materials. The selection of a method to synthesize the starting powders depends on the requirements for properties of the resulting composites.

Experimental studies were conducted to examine the drag forces in the finishing of ferromagnetic and paramagnetic samples shaped as bars with square and equilateral triangular cross-sections, having a side length of 16 mm. Variations in the total drag forces exerted by the magnetic abrasive tool (MAT), composed of magnetic abrasive powders of various types and particle sizes, on the movement of samples within large ring-shaped working gaps were analyzed to determine the percentage contributions of the drag force components. The drag forces most significantly depended on the midship section of the parts and were determined by the magnetic forces and the degree of powder compaction between the side surfaces of the samples and the pole tips. The drag forces associated with the midship section during magnetic abrasive finishing (MAF) constituted up to 60–65% of the total drag forces from the MAT side for ferromagnetic samples and 80–85% for paramagnetic samples. The contribution of friction forces unrelated to the action of magnetic forces did not exceed 10–15%. A significant share of the drag forces on the MAT side, reaching 25%, was attributed to the magnetic pressing of powder particle groups against the surfaces of ferromagnetic samples near the pole tips within the working area. The features peculiar to the movement of MAT particles in the finishing of ferromagnetic and paramagnetic parts were established. These features define the prevailing friction mechanisms in the finished surface–MAT contact areas, occurring between the side surfaces of the parts and the pole tips. Thus, sliding friction forces prevail in the finishing of ferromagnetic parts, whereas rolling forces dominate for paramagnetic parts, determining the conditions for forming finished surfaces through predominant microcutting or microplastic deformation.