Powder Metallurgy and Metal Ceramics最新文献

The evolution of the microstructure and phase composition of the Al–15 wt.% Fe powder alloy during pressing and sintering was studied. The structure of the starting powders, produced by melt atomization, was found to be multiphase and consisted of a solid-solution α-Al matrix and Al₆Fe and Al₁₃Fe₄ intermetallic compounds. The presence of the metastable Al₆Fe phase was attributed to the high cooling rates in the powder production by melt atomization. The sintering of green compacts prepared from the alloy powders involved negative shrinkage, which increased with higher sintering temperature, holding time, and compaction pressure for the starting samples. A potential cause of this phenomenon is the transformation of the metastable Al₆Fe phase into Al₁₃Fe₄, having a greater specific volume. Under solid-state sintering conditions at 500–600°C, the structure of the compacted samples remained fine-grained and included both the metastable Al₆Fe and stable Al₁₃Fe₄ phases. This promoted favorable conditions for achieving enhanced mechanical properties through the precipitation strengthening effect. In contrast, sintering at 800°C, accompanied by the formation of a liquid phase, led to recrystallization and formation of predominantly coarse Al₁₃Fe₄ crystals. This microstructural evolution diminished the strengthening effect provided by fine intermetallic phases. It was demonstrated that a sintering temperature of 600°C was optimal for retaining the metastable Al₆Fe phase in the alloy structure, allowing its transformation to be avoided and ensuring a controlled level of shrinkage during consolidation. The results may be useful for optimizing the technology for producing Al–Fe-based components with improved mechanical properties.

The effect of cold rolling deformation on the microstructure and mechanical properties of the spray- formed and extruded Al–9.8Zn–2.3Mg–1.7Cu alloy is investigated using various analysis methods, including electron backscatter diffraction (EBSD), tensile testing, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Two test schemes (heat treatment and deformation) were developed. According to the first scheme (SCA, solution treatment + cold rolling + aging), the material was treated at 480°C for 90 min, then quenched with water at room temperature, after which it was subjected to 10% cold rolling deformation and aged at 120°C for 24 h. The second scheme (SA, solution treatment + aging) involved treating the samples with a solution and aging at the same parameters as in the first group. The outcomes specified that compared to the solution-aging treated samples, the percentage of sub-grain in the cold rolling deformation treated samples increased from 33% to 66%. At the same time, the typical grain size reduced from 4.67 μm to 4.37 μm. The precipitate are more dispersed in the cold rolling deformation-treated samples. The dispersed deposits restrict the dislocation movement and promote the consistency of dislocation dispersal. Furthermore, the mechanical characteristics of the alloy are significantly boosted by the cold rolling deformation. Compared to the solution and aging procedure, the cold rolling deformation increases the tensile strength, yield strength, and sample elongation to new highs, from 655 MPa, 617 MPa, and 12.8% to 709 MPa, 683 MPa, and 13.2%, respectively. Fine-grain, precipitation, and dislocation strengthening are the primary strengthening mechanisms in the alloy.

Aluminum-based amorphous alloys and composites, which have tensile and compressive strengths approximately two to three times higher than those of crystalline Al alloys and composites, are very attractive for various potential industrial applications. However, the good glass formers in Al-based alloy systems are usually found away from the eutectic points in the phase diagram and thus exhibit poor glass-forming ability. Consequently, the glass-forming compositions require cooling rates of 10⁴–10⁶ K/s for synthesis via rapid quenching techniques, leading to dimensional restrictions in the micrometre to millimetre range. Synthesizing glassy powders and then consolidating them in the powder metallurgy (PM) route can improve the dimensions of these materials. Many researchers have made efforts to fabricate high-dimensional Al-based metallic glasses and composites with improved mechanical properties by using different PM routes. These research efforts require further review to enhance the development of Al-based glassy alloy systems for various potential applications. Researchers working on the development of high-specific-strength materials would benefit from such reviews. This review paper provides an in-depth examination of different techniques for fabricating Al-based metallic glasses and composites, their crystallization behavior, and mechanical properties. Suggestions for future research are provided to further enhance these materials.

The feasibility of producing composite powder ribbons in the Cu–Fe system by rolling was examined. Conventional techniques for producing Cu–Fe materials involve the melting of a copper– iron charge. Tehrefore, Cu–Fe composites commonly exhibit relatively low electrical conductivity under the combined effect of the high solubility of iron in copper at elevated temperatures and the slow diffusion kinetics of iron at lower temperatures. Powder metallurgy methods are an alternative to conventional techniques for producing copper–iron composites. They enable the synthesis of materials with the required chemical composition without reaching sintering temperatures that lead to a liquid phase, which prevents the formation of solid solutions in the Cu–Fe system. The influence of rolling parameters and subsequent densifying deformation on the properties of the powder materials was analyzed. Thermomechanical processing parameters were proposed to provide an optimal combination of mechanical properties in the rolled composite products. The mechanical properties of Cu–Fe powder sheet material produced by powder metallurgy were determined not only by the ratio of components but also by the content of oxide impurities in the starting powders. The reduction in the ductility of the rolled ribbons with increasing rolling strain was found to be associated with the accumulation of deformation-induced defects within iron particles and at the copper–iron interface. To mitigate the negative impact on the conductivity of solid solutions near interparticle contacts, the sintering and annealing temperatures for Cu–Fe composite ribbons should be maintained within the range 600–850°C.

The third part of the review describes wet chemistry methods that involve the application of pressure to the starting solutions. The synthesis of nanocrystalline powders from both unstabilized ZrO₂ and ZrO₂-based systems is discussed. The influence of acidic and alkaline environments on powder morphology is examined. Crystallization under hydrothermal conditions promotes the formation of hierarchical m-ZrO₂ nanorods. The properties of m-ZrO₂ powders produced by the reflux method and by hydrothermal synthesis in acidic and alkaline environments are compared. Hydrothermal homogeneous precipitation in the presence of urea is considered. Microwave heating is identified as an effective approach to increase the crystallinity of hydrothermally synthesized powders and to shorten the reaction time. The process of depositing ZrO₂ coatings on ZrB₂ powders and the hydrothermal corrosion method are described. In the solvothermal (glycothermal) method, organic compounds are used. The advantages of this method include the production of high-purity monodisperse powders. Spherical or rounded particles, nanorods, interconnected nanorods, and nanosheets are synthesized using this approach. Hydrothermal synthesis in supercritical conditions utilizes the properties of water at its critical point (374°C and 22.1 MPa), which facilitates uniform nucleation of primary nanoparticles. The particle morphology and size distribution are found to be influenced by parameters such as reaction temperature, pressure, time, precursor concentration, and pH. The powders synthesized with the methods reviewed are employed in the design of humidity and gas sensors, photocatalysts, functional materials for optical and medical applications, solid oxide fuel cells, thermal barrier coatings, and materials for the automotive industry.

Films/coatings of IV–VI group transition metal carbonitrides (TMCNs) were the subject of examination due to prominent properties characteristic of corresponding binary transition metal carbides and nitrides. The papers reviewed below concern the experimental and theoretical study of the structure, chemical bonding, mechanical (hardness, elastic modulus, wear resistance, tribology) and optical properties, thermal stability, and resistance to oxidation of transition metal carbonitrides in dependence on the deposition methods and conditions, composition, and thermal treatment. It has been shown that TMCN films can exist in two forms: as a solid solution with C and N atoms occupying the interstitial sites, and as a nanocomposite consisting of nanocrystalline TMCN phase embedded into an amorphous a-C or a-CN matrix. The first-principle calculations showed that the valence electron concentration (VEC), defined as the number of valence electrons per formula unit, is a significant indicator of the structural, thermodynamic and mechanical properties of TM carbonitrides. The overall results indicate a narrow region between VEC = 9 and 10, with TMCNs being ductile but demonstrating high hardness, mechanical, and thermal stability. As such, they are expected to exhibit the highest toughness. Experimental study confirmed the theoretical predictions and showed that the TMCN films/coatings exhibit rather high mechanical properties and low coefficients of friction, retain their structure upon annealing, and show high oxidation resistance. So, the films/coatings of IV–VI transition metal carbonitrides are promising materials for various technology applications.

The time dependence for densification of titanium nitride nanopowder during nonisothermal spark plasma sintering at an external pressure of 79.2 MPa in a nitrogen atmosphere was experimentally studied under controlled heating at a constant rate of 0.833 K/s. The densification kinetics was analyzed within the continuum theory of bulk viscous flow of a porous body using computational modeling. In general, the sintering process is characterized by a decrease in the root-mean-square stress within the porous body matrix to the limiting zero value as it approaches the nonporous state and by an increase in the root-mean-square strain rate following a curve with a maximum. Prior to the onset of densification, when thermodynamic temperature reaches 783 K, a stage involving annealing of the strain-hardened matrix forming the porous titanium nitride is observed. In the temperature range of 950–1040 K, weak densification occurs, governed by plastic flow, with a linear dependence of the strain rate on stress and low apparent activation energy (35.1 kJ/mol). At higher temperatures, dislocation climb becomes the acting mechanism, characterized by a power-law dependence (n = 2) of the root-mean-square strain rate on the root-mean-square stress, with an activation energy of 280.8 kJ/mol. The activation of this mechanism at relatively low temperatures, along with the nanosized structure, is attributed to the influence of the electric field. Titanium nitride samples produced by spark plasma sintering exhibit a nanosized structure with an average grain size of 60 nm, which ensures its enhanced mechanical properties.

A solid oxide fuel cell (SOFC) is an electrochemical device that consists of an anode, electrolyte, and cathode and directly converts the chemical energy of fuel–oxygen reaction into electrical energy. However, the high operating temperatures (700–900°C) required for effective ion transport lead to thermal degradation and chemical interactions between the fuel cell components. This issue can potentially be resolved only through the use of electrolytes with high conductivity at 500–600°C. Such materials include perovskite Ba₇Nb₄MoO₂₀. Nevertheless, its chemical compatibility with electrode materials remains poorly studied. In this regard, we examined the chemical compatibility of the Ba₇Nb₄MoO₂₀ electrolyte with CuO, CoO, and Fe₂O₃, as potential components of the Me_xO_y/Ba₇Nb₄MoO₂₀ anode, and with the Ba_0.5Sr_0.5Zn_0.2Fe_0.8O₃ cathode material using XRD analysis after annealing of the mixtures at 600–700°C for 10 h. The results show that Ba₇Nb₄MoO₂₀ exhibits low chemical compatibility with CuO, CoO, and Fe₂O₃, as interaction between the mixture components occurs already at 600–700°C. At 800°C, the Ba₇Nb₄MoO₂₀ phase either completely disappears or remains only in small amounts. Based on the residual content of the Ba₇Nb₄MoO₂₀ phase after annealing at different temperatures, its chemical compatibility with the studied metal oxides decreases in the following order: CoO > Fe₂O₃ > CuO. In the Ba₇Nb₄MoO₂₀– Ba_0.5Sr_0.5Zn_0.2Fe_0.8O₃ mixture, no interaction is observed at 600–700°C. At 800°C, the Ba₇Nb₄MoO₂₀ phase completely dissolves in Ba_0.5Sr_0.5Zn_0.2Fe_0.8O₃. Under typical cathode sintering parameters (950–1050°C, 3 h), chemical interaction between the electrolyte and the cathode also occurs, resulting in the formation of solid solutions based on BaNbO₃, SrMoO₃, and BaNb₂O₆.

The influence of the starting charge composition and forging process parameters on the structure, mechanical properties, and tribological performance of powder composites based on the Fe–Cr–C(B) system was studied. The composites were produced by hot forging of porous preforms prepared from a mixture of iron, ferrochrome, and titanium diboride powders. The structurization and mechanical properties of the composites were found to be primarily influenced by the production technology. It was also demonstrated that products with tailored functional properties could be fabricated by adjusting the technological parameters. The research findings showed that the content of doping elements in the starting charge influenced the physical and mechanical properties of the final products. The structure of composites produced by hot forging of porous preforms was similar to that of composites produced by liquid-phase sintering. However, the elemental composition of the structural components varied depending on the amount of TiB₂ in the starting charge. An increase in the titanium diboride content led to a decrease in the titanium content in carboboride, from 45–55% to 5–11%, and to the redistribution of other elements. It was further established that raising the hot forging temperature from 1100°C to 1200°C reduced the hardness of the composite from 76– 79 HRA to 70–71 HRA. The research allowed the determination of optimal technological parameters and charge compositions necessary to produce materials with low residual porosity and specified functional properties. These materials are intended for operation under high-load conditions or for the fabrication of tribological components.

The use of ZrB₂‒SiC and ZrB₂‒MoSi₂ ultrahigh-temperature ceramics with and without CrB₂ additions as antifriction materials for operation in dry friction conditions at high speeds and loads was examined. The friction process was studied under low-speed and high-speed sliding against a steel counterface at speeds of 2, 4, and 6 m/sec and loads of 0.8, 1.2, and 2 MPa. The surface structure and phase composition of the ceramic samples after friction were analyzed by X-ray diffraction, optical microscopy, and electron microscopy. Intensive tribooxidation of the composite components, along with the formation of an intermediate layer between the friction surfaces, was observed at a sliding speed of 6 m/sec. Wear followed a decreasing trend with increasing sliding speed at constant load. Analysis of the friction tracks using scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed an intermediate layer between the friction surfaces, consisting of tribooxidation products from both the ceramic and steel components. This layer reduced frictional losses, facilitated the formation of a smooth wear surface, and protected the brittle ceramics. Chromium diboride additions reduced the sintering temperature (through the formation of lower-melting compounds), increased the corrosion resistance (through the formation of zircon), and improved the mechanical properties of the composites (through the formation of solid solutions). The effect of these additions on the tribological properties of ZrB₂–SiC and ZrB₂–MoSi₂ composites was examined. The results showed that they favorably influenced the friction process and enabled the formation of a dense glass-like intermediate layer with complex phase composition. This layer demonstrated strong adhesion to the ceramic surface and promoted its self-restoration. The layer consists of tribooxidation products and metallic particles transferred from the steel counterface. The most significant reduction in the friction coefficient was observed for the ZrB₂–15% MoSi₂–5% CrB₂ composite, from 0.44 to 0.29.