Powder Metallurgy and Metal Ceramics最新文献

15 Cr ferritic oxide dispersion strengthened (ODS) steels are considered prime fuel cladding materials in nuclear reactors due to their excellent creep, swelling, and oxidation resistance. In the present study, the nominal compositions Fe–15Cr–2W–xY₂O₃ (x = 0, 0.3, 0.7, and 1.0) of ferritic ODS steels were prepared by mechanical alloying followed by spark plasma sintering. The sintered samples were annealed at different temperatures of 950, 1100, and 1250°C with a holding time of 60 min at respective temperatures. Further, the samples were also annealed at 1100°C for various durations of 0, 60, and 120 min. The role of varying yttria dispersoids and annealing temperatures on the grain growth kinetics, as well as their mechanical properties (hardness and compressive strength), were analyzed. The compressive strength of the sintered samples with varying yttria contents and at elevated temperatures of 600 and 700°C was determined. Modeling of compressive yield strength at room and elevated temperatures, as well as a correlation with the experimental values, were established for all the compositions. The grain growth exponent (n) and activation energy (Q) rose with the increase in yttria content and were estimated to be 11.52 and 612.91 kJ/mol, respectively, with 1.0 wt.% yttria. The grain size was nearly stable at the annealing temperature of 1100°C. A significant rise in compressive strength at room temperature and elevated temperatures was observed with a yttria reinforcement content of 0.7 wt.%. According to the strength model at different conditions, the role of ultrafine grains and dispersoids seemed to be predominant at room temperature and high temperatures, respectively.

The detonation spraying of coatings from fine composite materials is analyzed in the paper. The use of detonation coatings was found to improve the properties of machines and mechanisms and extend their life, while their functional performances are maintained over long-term operation. The structural features, strength, and fracture toughness of the coatings produced by multichamber detonation spraying from 75 wt.% Cr₃C₂ + 25 wt.% NiCr and Ni–Cr–Fe–B–Si (77–81.5 wt.% Ni, 10–14 wt.% Cr, 5–7 wt.% Fe, 2.0–2.3 wt.% B, 2.0–3.2 wt.% Si, 0.5 wt.% C) powder materials were examined. Changes in the detonation spraying parameters were proved to significantly influence the structure of the coatings: microhardness, phase composition, volume content of lamellae, sizes of grains and subgrains, phase formation, and dislocation density. The structural and phase state of the coatings was studied at all structural levels using a comprehensive approach, involving light and scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The prospects of the multichamber detonation spraying method, ensuring the necessary combination of structural and phase parameters of the coating material with a simultaneous increase in their physical, mechanical, and operational properties, were demonstrated. A high level of strengthening and fracture toughness of the coatings was promoted by optimal structural and phase constituents: fine grain and subgrain structure, uniform distribution of nanosized strengthening particles, and uniform dislocation density. The improved fracture toughness of the coatings is due to the absence of extended structural areas of dislocation clusters. The gradient-free distribution of dislocation density prevents the formation of local internal stress concentrators in the resulting coatings.

The powders produced by plasma-arc wire atomization in an argon atmosphere or air were studied for their use in 3D printing of complex-shaped metal parts and in granular metallurgy. The dependence of the morphology, structure, phase composition, and microhardness of the powders on the current and atomization conditions was established. In all studied operating modes of the plasma torch (180, 220, and 270 A), the atomized particles are predominantly spherical. The number of nonspherical particles increases with particle size. The powders atomized in an argon atmosphere exhibit a stable phase composition. The main component is iron aluminide Fe₃Al (or a mixture of Fe₃Al and AlFe). The α-Fe, Fe₃O₄, and Fe₂O₃ phases were also found. At currents of 220 and 270 A, the powder in –200+100 μm fraction contains the highest amount of aluminides, 83.88 and 86.30 wt.%, and the lowest content of oxides, 6.61–10.18 wt.%. In fine powders (–100+75 μm), the content of aluminides is 70.38– 28.3 wt.%), but the amount of oxides increases to 23.32–29.62 wt.%. The microhardness of oxide particles (5320–8150 MPa) is higher than that of metal particles (3070–4590 MPa). In atomization in air, the key components are Fe₂O₃, Fe₃O₄, FeO, and Al₃O₄. The total amount of oxides reaches 57.19–90.34%. The percentage of iron aluminides decreases significantly, and their maximum content (28.3 wt.%) is shown by the –315+200 μm powder at a plasma torch current of 270 A. In the finest powder fraction of –100+75 μm, the content of aluminides ranges from 6.2 to 15.36 wt.%. The average microhardness of metal particles is much lower (2750–4940 MPa) than that of oxide particles (4500–7460 MPa). It was found that the best material in terms of phase composition, structure, hardness, and shape factor was produced by atomization of a flux-cored wire in an argon atmosphere. In atomization in air, intense oxidation processes occur.

Pressed porous glass-ceramic carbon fiber biocomposites were produced from hydroxyapatite/glass and nanostructured carbon fibers. The specific features of the production process, as well as the composition, macrostructure, microstructure, and porosity of these biocomposites, were studied. The prospects for their medical applications, particularly in surgical osteoplasty, were identified. The starting materials included calcium phosphate glass ceramics derived from biogenic hydroxyapatite, featuring both bound and migrating glass phases, and activated nanostructured carbon fibers. The glass ceramics with a bound glass phase were produced by sintering powder mixtures of biogenic hydroxyapatite and sodium borosilicate glass, while those with a migrating glass phase were produced through mechanical mixing of biogenic hydroxyapatite and sodium borosilicate glass powders. The fine activated nanostructured carbon fibers used in the biocomposites were obtained by the mechanical grinding of a woven material from activated nanostructured carbon fibers. This material resulted from the controlled stepwise pyrolysis of hydrocellulose fabrics, followed by high-temperature vapor activation of the nanostructured fiber surface. To make cylindrical biocomposite samples, the fine activated nanostructured carbon fibers were blended with moistened mixtures of biogenic hydroxyapatite glass ceramics with bound and migrating glass phases and subjected to semidry pressing and incremental sintering with holding at 800°C. The selected process parameters enabled the production of pressed carbon fiber biocomposites with the desired composition and showed the ability to control their porous structure, achieving a relative density of 0.36–0.41, by regulating the behavior of the glass phases and the sintering of the reinforcing component. The biocomposite structures were examined by scanning electron microscopy. Energy-dispersive X-ray analysis was conducted to determine the chemical composition of the samples. The structures of the composites were analyzed and compared on the basis of their sorption capacities, determined from benzene adsorption–desoprtion isotherms using the gravimetric method. Analysis of the macrostructure, microstructure, and surface morphology of transverse and longitudinal sections of the biocomposites revealed a multiporous amorphous-crystalline microstructure, arising from the varying behavior of the glass phases, the presence of chaotically oriented short fine nanostructured carbon monofibers with diameters of several microns and a developed system of micro- and macropores on their surface, and spatial multidirectional hollow channels formed through the complete or partial combustion of the fibers.

Conglomerated (Ti, Cr)B₂–NiAlCrWCoMoTi composite powders for thermal spraying and deposition through sintering followed by milling were produced. The main processes stages in the production of powders, such as mixing, grinding, sintering, milling, and classification, were optimized. The effect of briquette sintering temperature on the milling efficiency and finished powder yield was determined. Solid-phase sintering was found to be feasible at temperatures 200–300ºC lower than the liquid-phase formation temperature. The influence exerted by the ratio of the refractory to metal components on the technological properties of the powders was studied. The flowability of the powders increased nonlinearly with a higher content of the metal component and greater particle sizes. The influence exerted by the ratio of the refractory to metal components on the morphology of powder particles was analyzed. The powder particles had a fragmentary elongated shape with a higher content of the refractory (Ti, Cr)B₂ component, while they acquired a more oval shape with a greater amount of the metal component. The composition and microstructure of individual powder particles were examined. They showed a heterophase microstructure. The uniform distribution of structural components in individual powder particles was found to depend on the mixing and grinding modes for powder mixtures. The uniform distribution of structural components in individual particles requires that particles of the starting powder components be significantly smaller (one-fifth or even less) than particles of the finished composite powder. The difference in the starting particle sizes for refractory and metal components should be no more than 2–3 times.

The thermal processes involved in the recrystallization within porous ultrapure iron compacts heated after cold pressing in a steel die were experimentally studied. The temperatures of recrystallization stages were shown to correspond to the heating behavior of metals and alloys. Depending on the heating rate of compacted powdered iron, various types of thermokinetic behavior were identified, indicating the nonlinear nature of interactions within the deformed powder body. Stages with both nonlinear and linear thermal behavior were present, as evidenced by the competition between several processes leading to the emergence of wave-like transfer of energy, accumulated while powdered iron deformed during cold pressing. The thermokinetic patterns observed in the heating of compacts, especially those made of pure iron, allowed all stages of relaxation in the deformed metal to be identified. The temperature profile in the heating process generally reflects the thermal state of the powdered metal, influenced by the additional release of energy accumulated in deformation. At some stages, heat release led to nonlinear processes, resulting in the occurrence of thermal waves. Both asynchronous and synchronous temperature changes were observed. In asynchronous behavior, nonlinear waves emerged. The superposition of relaxation processes in the generation of thermal waves is possible. At specific heating rates, the maximum amount of energy is simultaneously released in the relaxation and recrystallization processes, as testified by an increase in temperature to 550°C. The relaxation processes involve less energy compared to the recrystallization processes and the transition to the annealed state. In addition, after complete recrystallization, the onset of the sintering process was observed under temperature oscillations with damping.

The potential for amplifying tunnel magnetoresistance and magnetoimpedance in island nanofilms without energy consumption or the use of amplifying devices was studied. Such amplification was observed for the films deposited on a Gd₂O₃ layer instead of a glass substrate. The enhancement is due to the f–d exchange interaction established between atoms with unfilled f- and d-electron shells, present in both Fe and Gd₂O₃. The f–d exchange interaction enhances the ordering of the magnetic structure within the Fe ferromagnetic layer, increases its magnetization, and subsequently improves the properties that depend on this magnetization. Iron and Gd₂O₃ were selected because the magnetic moments of Fe in the iron group and Gd in the lanthanide series are among the highest effective ones: μ_Fe = 7.13 μ_B and μ_Gd = 7.95 μ_B. This, according to theory, determines the high energy of the f–d exchange interaction. The island morphology of Fe films deposited on a Gd₂O₃ layer enabled electron tunneling under the influence of the f–d exchange interaction. This allowed the study of tunnel magnetoresistance under direct current and magnetoimpedance under alternating current influenced by the f–d exchange interaction. The frequency dependence of the active component Z', the reactive component Z'', and the total impedance Z of Fe films on glass and Gd₂O₃ substrates, without and under a constant magnetic field of 7500 Oe, was analyzed. These characteristics are used to determine the frequency dependence of tunnel magnetoimpedance and estimate tunnel magnetoresistance for Fe island films on glass and Gd₂O₃ substrates. These characteristics were found to be 55 % higher, on average, for Fe deposited on Gd₂O₃ than for Fe on glass, both at a low frequency of 0.1 Hz for tunnel magnetoresistance and at higher frequencies of 1–10⁵ Hz for tunnel magnetoimpedance. This results from the influence of f–d exchange interaction on electron tunneling between the iron islands.

In this study, the creep behavior, mechanical properties, and microstructure evolution of AA 1050/SiC/Cu composite strips fabricated by accumulative roll bonding (ARB) process are experimentally investigated. All specimens were fabricated with different SiC wt.% with a maximum of eight cumulative cycles of ARB. The study of creep behavior and mechanical properties showed the formation of a 17 μm atomic diffusion layer at the interface during ARB under three creep loading conditions, namely 35 MPa at 225°C, 35 MPa at 275°C, and 30 MPa at 225°C. An intermetallic compound formed near Al, resulting in a 40% increase in interface thickness with increasing temperature at constant stress. However, the creep failure time decreased by 44% and the stress level decreased by 13% at a constant temperature without any significant effect on the interface thickness. In different conditions, it was observed that at a constant temperature with an increase in stress level, the second steady state creep rate of the creep curve reaches to 39%, while it decreases to 2% with a small increase in temperature. It can be concluded that the applied temperature and stress affect the creep properties and especially lead to an increase in the steady-state creep rate of the creep curves with higher stresses. This trend was the opposite for the creep temperature at higher temperature levels. Furthermore, dynamic recrystallization was observed through the crystalline structure of the samples.

The tribotechnical properties of the Cu–(4–6) wt.% Ni–(1–1.5) wt.% Ti–(7–10) wt.% Al–(0.5–0.8) wt.% Si‒(5–8) wt.% CaF₂ antifriction composite were studied. The effect of tribofilms that form and evolve in the friction process in air at loads of 2.0 MPa and rotational speeds from 5,000 to 15,000 rpm on the tribological properties was analyzed. The evolution of dissipative tribofilms and the counterface occurs through a bifurcation mechanism with a transition to one of two attractors, depending directly on the high-speed loading modes. At speeds of 5,000–13,000 rpm, a continuous homogeneous lubricating layer forms on the contacting surfaces. Electron microscopy and elemental mapping of the tribofilm confirmed that the distribution of elements was uniform, promoting high antifriction properties and a sustained self-lubrication mode. With increase in the rotational speed to 15,000 rpm, the system exhibits a self-organization effect in the formation of a coarse heterogeneous tribofilm. This tribofilm loses its continuity and is an accumulation of phases, leading to a sharp decline in antifriction properties. The dual formation of tribofilms is decisively influenced by operating conditions, particularly the intensity of external energy. Depending on this energy, tribofilms show different structures and manifest in two functionally opposite types, transforming from antifriction films to friction ones, resulting in significantly different tribotechnical properties. Copper-based antifriction composites can be recommended as an effective alternative to cast bronzes for operation at rotational speeds of 5,000–13,000 rpm and loads of 2.0 MPa in the friction units of forming, printing, and offset cylinders in high-speed printing equipment.

Experimental studies were conducted to refine the theoretical provisions concerning the mechanism and kinetics of penetration for a metal melt consisting of destructive reagents, such as gallium, indium, tin, and zinc (destructive composition), along the grain boundaries in unstressed metal samples. It was experimentally confirmed that the penetration rate of the destructive composition was limited by processes at the liquid phase front, including dissolution of intergranular boundary areas, recrystallization to form solid solution crystals, and opening of new crack areas under the pressure of growing crystals. The experimental findings indicated a significant decrease in the strength of aluminum alloys resulting from the effect of the destructive composition. Analytical dependences and corresponding empirical coefficients characterizing the effects of the destructive composition on structural aluminum alloy elements under tensile loads were derived. These empirical coefficients enable the determination of conditions under which aluminum alloy structures fail under the influence of destructive compounds, considering the tensile stresses. The effect of the destructive alloy on the onset of fatigue damage and the durability of aluminum alloy structures under asymmetric cyclic stresses was examined. Significant reduction in the fatigue strength of aluminum structures under the influence of the destructive composition was experimentally confirmed.