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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. [ABSTRACT FROM AUTHOR] more...

The influence of heat treatment temperature of the starting powders, ranging from 400 to 1450°C, on the consolidation of zirconia-toughened alumina (ZTA) composites was studied. In these composites, particles of a ZrO2 (Y2O3, CeO2) solid solution with high fracture toughness are dispersed in an Al2O3 matrix. The powders for developing the ZTA composites (wt.%)—90 Al2O3–10 (ZrO2 (Y2O3,CeO2) (90 AZK) and 70 Al2O3–30 (ZrO2 (Y2O3,CeO2) (70 AZK)—were produced using a combination of hydrothermal synthesis and mechanical mixing. Cold uniaxial pressing and sintering in air at 1600°C for 1.5 h were employed for the consolidation. The sintered materials were examined by X-ray diffraction and scanning electron microscopy. The compaction of the composites was associated with the brittle fracture of hard sintered agglomerates (for 90 AZK) and with the plastic deformation effect (for 70 AZK). The sintering of the 90 AZK and 70 AZK composites was accompanied with ZrO2 phase transformations, abnormal growth of the Al2O3 grains, and zonal segregation effect. The Zener pinning effect in the 70 AZK composites inhibited the abnormal growth of Al2O3 grains. The increased porosity of the 90 AZK composites was due to the bimodal distribution of the starting powder agglomerates in accordance with the shape factor. The Vickers hardness of the 90 AZK samples varied from 6.4 to 4.4 GPa and that of the 70 AZK samples from 10.3 to 7.2 GPa. The decreased hardness of the 90 AZK composites was attributed to the formation of a two-scale porous microstructure. The topological memory of the ceramics was demonstrated to determine the conditions for microstructural design of advanced ZTA composites for tool, structural, and functional purposes with the required properties. [ABSTRACT FROM AUTHOR] more...

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. [ABSTRACT FROM AUTHOR] more...

The paper examines how cold isostatic pressing (CIP) of powder samples preformed by uniaxial pressing at up to 0.4 GPa influenced the density, coercive force, structure, hardness, and phase composition of the WC–8 wt.% Co (VK8) hardmetal after sintering in vacuum. A multiplication installation was employed for cold isostatic pressing. Transformer oil served as the pressure transmission medium. The density of the CIP samples increased linearly with pressure prior to sintering and reached its maximum at 0.2 GPa for the sintered CIP samples. The coercive force increased nonmonotonically with pressure. The WC grains refined when CIP pressure increased to 0.2 GPa but slightly coarsened after CIP at 0.3 and 0.4 GPa. The Co layer became thinner with pressure being increased to 0.3 GPa and slightly thicker at a pressure of 0.4 GPa. An intermetallic Co0.8W0.2 phase emerged in the samples subjected to preliminary CIP at 0.4 GPa. Hardness measurements at different loads up to 300 N showed that hardness increased at CIP pressures up to 0.3 GPa and slightly decreased in CIP at 0.4 GPa. Scanning electron microscopy photographs of the indenter imprints showed massive cracking of the WC grains. The results were analyzed using experimental data published previously on the effect of high isostatic pressure on the multiplication of dislocations and the fracture of single crystals. Those papers found that the deformation and fracture of single crystals under high isostatic pressures were accompanied by a sharp increase in the dislocation density. Each WC particle was compressed from all sides by the neighboring WC and Co particles, resulting in quasi-isostatic compression. However, the compressive forces are not equal in quasi-isostatic compression conditions, and there is always one force that is greater than the others. This force causes deformation or fracture leading to the mechanical activation of the powder because the imperfection of its particles increases and in turn influences the properties acquired by the hardmetal. [ABSTRACT FROM AUTHOR] more...

The efficiency and durability of a diamond tool fabricated using powder metallurgy methods depend on several factors. These are the quality of diamond materials, composition of a bond and its physicomechanical and physicochemical properties, as well as the nature and structure of the initial metal powders for sintering of a diamond-composite material, i.e., a functional element of a diamond tool. This paper examines the dispersion influence of the initial metal powders on the hot-pressing sintering process in two metal systems, Fe–Cu–Sn–Ni and Cu–Ti–Sn–Ni. In the first case, the initial charge was a mixture of independent Fe, Cu, Sn, and Ni metal powders. In the second case, we used the powder of the Cu–Ti–Sn–Ni alloy, previously melted and dispersed in ball mills. The effect of dispersion, size distribution, morphology, average mass diameter on the density, and hardness of sintered metal samples was then studied. It was revealed that the sintering capacity and features of the sinters are directly dependent on the dispersion of the initial powders for the Fe–Cu–Sn–Ni system. In contrast, the initial charge is a classical mixture of individual metallic powders. When using powders of Cu–Ti–Sn–Ni alloys, the revealed dependence of the dispersion of the initial powder in the alloy on sinterability and properties of the sinters is no longer observed. During the experiment, reverse phenomena were established. Thus, the best results were achieved when using a coarse grain size of the alloy powder. In this work, we showed the possibility of producing pre-melted alloy powder of a planned composition based on copper (Cu ≥ 77%) Cu–Ti–Sn–Ni with a Ti content >10% by mechanical activation for the further successful implementation as a binder of diamond tools. [ABSTRACT FROM AUTHOR] more...

Valerii Skorokhod's published papers focusing on experimental and theoretical studies of fine powder sintering are analyzed. The application of Skorokhod's rheological theory of sintering to analyze the sintering kinetics of fine tungsten powders is described. The history of discovering and explaining a fundamentally new phenomenon of locally nonuniform densification in the sintering of actual powder bodies and the effect of this phenomenon on the subsequent sintering process are outlined. The reasons for which the physical theories of sintering could not be fully consistent with the experimental sintering of actual powder bodies are addressed. The structurization processes are found to have a predominant effect on the kinetic and thermodynamic densification factors in sintering. [ABSTRACT FROM AUTHOR] more...

The paper examines the effect of high-energy grinding and post-treatment conditions on the structure and physical and mechanical properties of iron aluminide Fe–15 wt.% Al obtained by sintering and impulse hot pressing. It was shown that the grinding of a mixture of iron and aluminum powders in a planetary mill results in the formation of lamellar particles whose morphology is preserved in the alloy structure after sintering and impulse hot pressing. After grinding, sintered intermetallic compounds obtained from powder mixtures demonstrate low physical and mechanical properties due to the low quality of grain boundaries. The use of impulse hot pressing for compaction of samples from milled powders at temperatures of 850–1150°C significantly increases the density of intermetallic compounds compared to sintered materials of a similar composition—from 5 to 6.5 g/cm3. The increase in the temperature of impulse hot pressing contributes to an increase in mechanical characteristics, where the maximum values of bending strength and fracture toughness are 880 MPa and 21 MPa · m0.5, respectively. Subsequent hightemperature annealing (1350–1450°C) leads to an improvement of the quality of grain boundaries with the formation of a predominantly discontinuous grid, coagulation of impurity segregation, and, as a result, to a sharp increase in bending strength and fracture toughness, which are 1400 MPa and 27 MPa · m0.5, respectively. It was shown that the interparticle rupture observed in the samples after impulse hot pressing at relatively low temperatures changes to transcrystalline after hightemperature annealing. [ABSTRACT FROM AUTHOR] more...

The paper examines the impact of heating temperature and isothermal holding time during sintering in a vacuum on the phase composition, structure, and mechanical properties of Fe3ipt>Al iron aluminide synthesized from a mixture of iron and aluminum powders. Dilatometric studies have shown the complexity of occurring changes in the density of the billets during sintering. First, the porosity increases from 15% in the initial billet to 45% during sintering at 950°C, and after decreases to 5% at a sintering temperature of 1450°C. The synthesis of intermetallic compounds at powder mixture heating was examined by the X-ray diffraction method. It was shown that up to 30% of intermetallic compound Fe2Al5 is formed during an hour-long isothermal holding at 600°C. Increasing the holding time to 3 hours or temperature to 950°C results in the formation and gradual growth of FeAl (B2) aluminide content. With a further increase of sintering temperature up to 1450°C, the amount of A2 phase becomes bigger, and concentration of iron and aluminum in it approaches to stoichiometric ratio Fe3Al. The mechanical properties of iron aluminide intensify with increasing sintering temperature, especially rapidly after sintering at 1450°C, when planar pores close and perfect interparticle contacts form. [ABSTRACT FROM AUTHOR] more...

The densification of a powder mixture containing titanium diboride and 20 wt.% molybdenum disilicide during nonisothermal spark plasma sintering was experimentally studied. The sintering process was assisted with an external pressure of 50.93 MPa in vacuum at a controlled constant heating rate of 1.67 and 2.72 K per second. It was established that sintering occurred when the thermodynamic temperature reached 1155 K, which should be taken as the critical brittle–ductile transition temperature for molybdenum disilicide, a less refractory material. The densification kinetics was analyzed using the continuum theory for bulk viscous flow of a porous body, considering the effect of powder particle shape on the rheological properties of the sintered body. In general, the sintering process was characterized by a decrease in the root-mean-square stress within the porous body matrix to the limiting zero value as it approached the nonporous state and by an increase in the root-mean-square strain rate along the curve with a maximum. Computational modeling of the densification kinetics for the powder composite, involving determination of the activation energy for viscous flow of the composite matrix as a function of temperature and root-mean-square stress, allowed the initial, low-temperature, and medium-temperature stages of spark plasma sintering to be identified. At the initial stage up to 1220 K, the activation energy increased nonlinearly and sharply, which can be caused by active spark flashes with the formation of plasma within the loose random packing of the powder particles, as a similar stage is not observed in conventional pressure assisted sintering. At the next low-temperature temperature stage, the activation energy increased as the root-mean square stress decreased. In the temperature range from 1300 to 1389 K, the activation energy for viscous linear flow of the composite matrix was 223 kJ/mol. In the medium-temperature range from 1414 to 1485 K, the activation energy increased to 255 kJ/mol. [ABSTRACT FROM AUTHOR] more...

The paper overviews experimental and theoretical studies focusing on the sintering of cermet and ceramic bodies conducted and published from 1922 to 1967. Special attention is paid to the generation and evolution of new ideas, elements of the physical theory of sintering, and attempts to use the entire wealth of knowledge in solid-state physics and physical mechanics available in a given time period. Analysis of the accumulated knowledge on sintering phenomena and the actual contribution of individual researchers to this process may promote further improvement of the physical theory of sintering and its advance to applied problems of powder materials. The key role of theoretical physicists, Frenkel, Herring, and Lifshits, in resolving the most complex problems of sintering science is emphasized. [ABSTRACT FROM AUTHOR] more...

The papers focusing on experimental and theoretical studies on sintering kinetics of real powder systems that were published in the 1940s-1950s are analyzed. Two major concepts explaining the nature of the so-called activity shown by metallic powders and some inorganic powders during sintering are addressed in detail. One concept deals with the key role of plastic flow mechanism and the other gives preference to the role of crystal lattice defects formed in powder particles when produced in nonequilibrium conditions. The reasons why neither of the concepts can underlie the physical theory of active sintering, being in full agreement with the experiment, are ascertained. [ABSTRACT FROM AUTHOR] more...

The use of the hydrogenation and disproportionation (HD) and desorption and recombination (DR) route (HDDR) for sintering Nd2Fe14B-based ferromagnetic alloys, such as Nd11.7Fe81.1Zr1.2B6 and Nd16Fe73.9Zr2.1B8, was studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The dependence between the production conditions—grinding of the alloys into powders, compaction pressure of the powders, hydrogen pressure and temperature at the first stage of sintering in hydrogen (HD), and temperature at the second stage of sintering in vacuum (DR)—and the porosity and microstructural particle size of the sintered materials was evaluated. The powders were ground in hydrogen in a planetary-ball mill at 200 rpm for 1 h and compacted at 2, 5, and 6 t/cm2. The first sintering stage was carried out at a hydrogen pressure of 0.05 MPa and a temperature of 760°C, and the second stage at 850 and 950°C. The powders were found to sinter at the first stage. The porosity of the sintered materials decreased with increasing compaction pressure. The grain size of the ferromagnetic Nd11.7Fe81.1Zr1.2B6 phase in the sintered materials ranged from 100 to 300 nm. The physical mechanism behind the reduction in the sintering temperature was attributed to an increase in the diffusion rate of alloy components resulting from hydrogen-induced phase transformations, such as disproportionation and recombination, and to the presence of a hydrogen solid solution at both stages of the process, HD and DR. A very important aspect of this research is that the powders were sintered under low hydrogen pressure required to produce magnetically anisotropic materials. Problematic aspects of the properties shown by the sintered materials, particularly microstructural heterogeneity, were analyzed, and approaches to their solution, through homogenizing the particle size of the powders and optimizing the HDDR parameters (hydrogen pressure, temperature, reaction time), were proposed. The process advantages of the new sintering method compared to similar techniques included the temperature lower by more than 100°C, the potential for producing nanostructured anisotropic materials, and the use of technically simpler and cheaper sintering furnaces. [ABSTRACT FROM AUTHOR] more...

The densification of a fine-grained tungsten carbide cermet containing 36 wt.% copper binder during impact assisted sintering in a vacuum at thermodynamic temperatures of 1023, 1123, and 1223 K with an initial impact velocity of 6.4 m/s was studied. Based on the experimental data and calculated elastic properties of the samples and the impact machine, computational modeling of the densification dynamics with a trial and error method was carried out using a third-order dynamic system in combination with the rheological model of Maxwell's viscoelastic body, and as a result previously unknown values of shear viscosity for material cermet matrices were obtained. The time dependences of force, compression, velocity, and acceleration of the system, as well as shrinkage, root-mean-square stress, and strain rate, of the cermet samples during impact assisted sintering were determined. The calculated phase trajectory of the dynamic system movement showed that the initial kinetic energy of the impact was not completely exhausted for the irreversible densification of the cermet samples. Part of the energy dissipated in the environment after the rebound of the machine's impact parts. At the initial stage, the system exhibited nonperiodic (atemporal) damping during its movement at high ratios between the system's stiffness and the cermet samples' viscous resistance. As the ratio decreased, the movement transformed into damping oscillations. The work of densification and the thermomechanical effect, which significantly increased the temperature of porous samples, were evaluated. The estimated activation energy of the viscous flow for the porous cermet matrix was 0.34 eV or 33 kJ/mol that indicated the dislocation mechanism of sintering. The samples produced by impact assisted sintering showed significantly higher strength values compared to pressureless sintered samples at a higher temperature. [ABSTRACT FROM AUTHOR] more...

Scanning electron microscopy and X-ray energy-dispersive spectroscopy were employed to study the sintering of powders from the induction-melted industrial ferromagnetic Sm2(Co,Fe,Zr,Cu)17 alloy by the hydrogenation, disproportionation (HD), desorption, recombination (DR) (HDDR) route. The HD stage proceeded at 700°C and DR at 950°C. The experimental results showed that sintering of the powders occurred at the HD stage to produce a mechanically integral highly porous material. The porosity of the sintered materials was found to decrease as the compaction pressure and powder particle refinement increased. The powder compaction pressure was estimated to range from 2 to 5 t/cm2. The decrease in sintering temperature was attributed to the higher diffusion rate of the alloy components resulting from the decrease in particle size, hydrogen-initiated phase transformations, and the hydrogen solid solution present in the alloy. Phase transformations occurred when the pressure changed at high temperatures. If the hydrogen pressure was high, the intermetallic was not thermodynamically stable and disintegrated (disproportionated) into several phases. If the hydrogen pressure was low (vacuum), the rare earth metal hydride was thermodynamically unstable and disintegrated, while the rare earth metal interacted with other phases to form the starting intermetallic. These phenomena are due to chemical reactions within a solid body, proceeding through the diffusion of components. The new sintering method for ferromagnetic materials has process advantages over existing methods: it does not require holding at the highest heating temperatures or usage of complex dies or complex equipment and results in the production of anisotropic nanostructured materials. Ways to improve the properties of sintered materials at low temperatures (in particular, increasing the homogeneity of their microstructure and decreasing the porosity) are proposed, such as optimization of sintering parameters and homogenization of the powders by particle size. [ABSTRACT FROM AUTHOR] more...

The paper examines how the shock sintering temperature and carbon content of the VK25 hardmetal and the process time and discharge energy in the electrospark deposition of the hardmetal onto steel 45 samples influence the mass transfer, thickness, and microhardness of the resultant surface layers. The experiments were performed employing an Elitron-24 unit providing a discharge energy of 0.34–1.1 J. The VK25 hardmetal was produced by shock sintering in the range 1150–1300°C using WC with different carbon contents. For the maximum mass transfer, the hardmetal sintering temperature should be 100–150°C lower than the temperature at which samples with the highest strength were produced. The maximum mass transfer was observed when the hardmetal was depleted of carbon (3.9 instead of estimated 4.59 wt.%). A protective layer 100–200 μm thick, with a hardness of 8.0–13.7 GPa, was produced on the steel samples. [ABSTRACT FROM AUTHOR] more...

The paper examines how the titanium diboride content of the starting TiH2–TiB2 powder mixture influences basic mechanical properties of the resultant sintered composites in tension and compression tests. The porosity of the compacts sintered at 1250°C increases with greater titanium diboride content of the starting mixture, which is associated with the Frenkel effect that occurs in the sintering process. Although the porosity somewhat increases, the strength, hardness, and elastic modulus in tension become higher when 5% TiB2 powder is introduced into the charge. These characteristics however decrease when the high-modulus component increases to 10% in the charge. The ductility of the sintered alloys monotonically reduces with higher boride content. The yield point and compressive strength monotonically increase with higher TiB2 content of the charge, despite greater porosity. This occurs because porosity has a significantly weaker effect on the strain resistance of the sintered Ti–TiB composites in compression than in tension. [ABSTRACT FROM AUTHOR] more...

The paper examines how the preliminary grinding of titanium hydride and the sintering temperature influence the mechanical characteristics of resultant titanium. The powder refinement is the dominant factor that defines the properties of titanium. The strength of titanium increases to 2470 MPa at the highest grinding energy, but its ductility is only 1–2%. The effect of sintering temperature is not so simple: there are two temperature ranges in which temperature dependence of the mechanical properties differs. At low sintering temperatures (780–800°C), the fine and active titanium particles resulting from the dissociation of titanium hydride lead to the rapid formation and growth of interparticle contacts. At high sintering temperatures, the densification of material increases by several times and, hence, impedes the removal of impurities from porous space. Rapid grain growth and dissolution of impurity oxygen in the titanium lattice occur in parallel, sharply increasing the strength and decreasing the ductility of titanium. The ratio of the grain growth and oxygen dissolution rates determines the resultant mechanical properties. [ABSTRACT FROM AUTHOR] more...

The effect of TiB2 additions on the structure, phase composition, and mechanical and tribological properties of materials in the Fe–FKh800 system was studied. The introduction of titanium boride additions activated compaction of the iron-based composites through sintering with participation of the liquid phase that emerged with the formation of low-melting Fe–C–B (Tm ~ 1050°C) and γ-Fe–Fe2B–TiB2 (Tm ~ 1162) eutectics and led to a 50–70°C decrease in the sintering temperature of the compacts. Titanium boride additions between 0.38 to 0.74 wt.% provided 20–25% higher bending strength of the 65 wt.% Fe–35 wt.% FKh800 composite with a slight increase in hardness. Metallographic studies, X-ray diffraction, and electron microprobe analysis of the Fe–35 wt.% FKh800–TiB2 materials showed that titanium boride additions promoted a multiphase, microheterogeneous matrix-reinforced composite, consisting of Kh17 chromium steel, double M7C3 and M3C iron–chromium carbides, and complex Me3(CB) carboborides. The influence of TiB2 additions on the wear resistance of the composites subjected to dry friction against fixed diamond wheel particles and ShKh15 steel was studied. The study showed that the abrasive mass wear (Im) of carbide steels decreased from 36.94 to 14.8 mg/km and their linear wear (Il) decreased from 0.197 to 0.079 mm/km with TiB2 additions increasing from 0.38 to 1.48 wt.%. Titanium boride additions ranging from 0.38 to 2.2 wt.% reduced the mass wear rate from 4.9 to 1.9 mg/km in dry friction of the composite against a ShKh15 steel counterface with 50–55 HRC hardness and decreased the friction coefficient from 0.49 to 0.38. [ABSTRACT FROM AUTHOR] more...

Spark plasma sintering (SPS) has been an attractive technique for many researchers seeking to consolidate metals and ceramics. This technique's high heating rates with the support of simultaneous applied pressure result in highly densified materials. One of the most important effects of a high heating rate is the limitation of grain growth, which results in enhanced mechanical properties. Recently, a relatively new form of SPS with its own unique advantages was developed and is most commonly referred to as pressureless spark plasma sintering (PSPS). There has been an increase in the usage of this method in several applications such as porous material production, sintering of materials with a finer grain structure, and consolidation of green bodies in a short time. Although there have been many studies on PSPS, there is currently no review of the pressureless applications of SPS. This paper provides a link from SPS to PSPS and discusses the different applications in some detail. [ABSTRACT FROM AUTHOR] more...

In this work, SiC ceramics were prepared by spark plasma sintering (SPS) using alumina and rare earth oxides (RE2O3, RE = Gd, Y, Sc) as liquid phase sintering additives. Displacement shrinkage curve with the temperature, as well as with temperature and time, has been drawn by recording the displacement, time, and temperature of the device's indenter Then, the shrinkage displacement curves were employed to investigate the sintering process. The microstructure and the phase composition of the sintered samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrate that the sintering process involves physical shrinkage, gas expansion, displacement stagnation, and liquid phase formation. The maximum linear shrinkage occurred at the stage of liquid phase formation. A similar trend for shrinkage displacement curve formation was observed at the first three stages for all samples. At the same time, different shrinkage temperatures and shrinkage rates were noticed on the fourth stage. After sintering, equiaxed grains with a grain size of about 1–2 μm were observed for all samples. The extremely high heating rate and short holding time of the SPS process prevent grain growth. Secondary phase Y3Al5O12/Gd4Al2O9 formed with Al2O3 + Y2O3 and Al2O3 + Gd2O3 additives, respectively, was used as liquid phases. Sintered samples exhibited superior mechanical properties, high electrical resistance, and lower thermal conductivity due to the low conductive secondary phase and small grain size. [ABSTRACT FROM AUTHOR] more...

Copper–iron alloys are used as structural, electrical contact, and elastic materials and those for the protection against electromagnetic waves. They have wide prospects for applications in electronics and in the manufacture of semiconductors, automotive parts, and medical equipment. Conventional methods for producing Cu–Fe alloys by melting and for processing Cu–Fe alloy ingots have some restrictions caused by the segregation of components when the ingots are solidified. The potential use of powder metallurgy methods to produce copper–iron materials is shown. Powder materials with uniform distribution of iron inclusions in a copper matrix are prepared by rolling. The influence of conditions used to form powder ribbons by rolling of the Cu–Fe powder mixture on the distribution of alloy components in the rolled structure was studied. The conditions of sintering and heat treatment of compact copper–iron powder materials and their effect on the mechanical properties of the rolled material with 15% Fe were analyzed. To impart the maximum possible conductivity to the Cu–Fe material, the influence of cold hardening should be minimized and the formation of Cu–Fe solid solutions should be excluded. The influence of the composition (if the formation of solid solutions is excluded) will be practically determined by only the iron content. The effect of cold hardening is reduced by heat treatment of the Cu–Fe ribbons after rolling. Shear deformation in the rolling process and temperatures of sintering and annealing in the range lower than the melting points of components in the Cu–Fe system exclude the active formation of solid solutions and impart the required mechanical properties to the sheet materials. [ABSTRACT FROM AUTHOR] more...

Abstract  The paper examines the geometrical evolution and particulate interaction in WC-Co alloys produced by solid-phase sintering. It is shown that solid-phase sintering actively modifies the geometric structure: carbide particles grow, become facetted and grow together, and the cobalt phase is redistributed. The WC particles grow irregularly over different temperature ranges. The low rate of growth is characteristic of temperature ranges between 1050 and 1200°C. When alloys are sintered at 1200°C and higher temperatures, the growth of tungsten carbide particles intensifies substantially (by four times). Hence, the temperature 1200°C separates two structurization areas in solid-phase sintering. At this temperature, there is a bend on the specific resistivity curve, which is evidence of higher-quality grain and phase boundaries. [ABSTRACT FROM AUTHOR] more...

The effect of Y2O3 and Y2O3–SiO2 additions on the spark plasma sintering (SPS) of α-Si3N4 was studied. The interaction of oxides with silicon nitride and their influence on the α → β phase transformation in silicon nitride in the sintering process were analyzed. The Y2O3–SiO2 sintering activator was shown to significantly intensify the consolidation at 1800°C through the formation of 18–25 vol.% liquid Y2Si2O7 and Si2N2O. This significant amount of the liquid phase was responsible for the rearrangement of nanosized Si3N4 grains under pressure. In contrast, the consolidation of Si3N4–Y2O3 was much slower, and prolonged exposure to high temperatures led to significant grain growth. Optimization of the spark plasma sintering (SPS) parameters (variation in compaction pressure, heating rate, and holding time relative to temperatures of active shrinkage) allowed the total time of high-temperature treatment to be decreased and dense ceramic samples (≥ 98%) to be produced. The phase composition of virtually porousless ceramic samples produced in the optimized SPS conditions (1800°C, 5 min) with a complex Y2O3–SiO2 activator was as follows: 72.4 vol.% β-Si3N4, 11.0 vol.% α-Si3N4, 14.2 vol.% Si2N2O, and 2.4 vol.% γ-Y2Si2O7. The ceramic samples had isotropic 300 nm grains and anisotropic ~2 μm long grains. When only yttria was added to silicon nitride, dense ceramic samples were produced at 1800°C with 20 min holding and consisted of 85 vol.% β-Si3N4 and 15 vol.% α-Si3N4. The isotropic Si3N4 grains were 750 nm in size on average and anisotropic grains were ~3–4 μm in length. The same dense ceramics could be produced by SPS at 1950°C for 5 min but contained only β-Si3N4: i.e., the α → β phase transformation was complete. The dense β-Si3N4 ceramics activated with only Y2O3 and Y2O3–SiO2 demonstrate high room-temperature bending strength (~950 MPa), HV10 hardness (~15.3 GPa), and fracture toughness (5.7 MPa · m1/2). [ABSTRACT FROM AUTHOR] more...

The production of ZrN–Si3N4 and ZrN–Si3N4–TiN composites by spark plasma sintering and the mechanical and tribological properties of the consolidated materials were studied. The densification of the ZrN–Si3N4–TiN composites was found to proceed more intensively in the range 1100–1300°C, and nanocrystalline titanium nitride was the main factor that promoted the densification of these composites. Ceramic 57 wt.% ZrN–43 wt.% Si3N4 and 84 wt.% ZrN–16 wt.% Si3N4 samples with a relative density of 0.95 and 0.93 and (84 wt.% ZrN–16 wt.% Si3N4)–15 wt.% TiN and (57 wt.% ZrN– 43 wt.% Si3N4)–30 wt.% TiN composites with a relative density of ~0.98 were produced. Microstructural studies showed that components of the consolidated ZrN–Si3N4 composites were uniformly distributed over the material with an average grain size of 200–300 nm. The ZrN–Si3N4– TiN composites had a finer structure, TiN grains being smaller than 100 nm. The mechanical properties of the titanium nitride composites were higher than those of the ZrN–Si3N4 materials. Thus, the Vickers hardness and indentation-determined fracture toughness of the composites containing 15 and 30 wt.% TiN were 18.7 ± 1.1 GPa and 5.2 MPa ∙ m1/2 and 19.1 ± 1.9 GPa and 5.8 MPa ∙ m1/2, respectively. The hardness of the ZrN–Si3N4 composites was ~17 GPa. The tribological properties of the composites were tested with the VK6 hardmetal and silicon nitride. The wear resistance of the ceramic samples directly depended on the contents of zirconium nitride and counterface, i.e., on their physicochemical interaction. When the ZrN content increased to 84%, the tribological properties of the composites improved substantially through the lubricating capability of zirconium nitride. The (84 wt.% ZrN–16 wt.% Si3N4)–15 wt.% TiN composite showed the best tribological properties and can be recommended for use in friction units under dynamic loads. [ABSTRACT FROM AUTHOR] more...

The interaction in the Ni–Ti–B and Ni–Ti–B–Cr systems along the Ni–TiB2 and (Ni–20% Cr)–TiB2 sections was studied. Solid-phase interaction was not found to occur for Ni–TiB2 up to 1200°C. In the case of (Ni–20% Cr)–TiB2, a new phase was formed, Cr2B, with a thickness of ~5 μm at a temperature of 1200°C. The contact melting began above 1200°C in the Ni–TiB2 system and above 1180°C in the (Ni–20% Cr)–TiB2 system. In the (Ni–20% Cr)–TiB2 system, the emerged liquid wetted titanium diboride with an angle of 50°; when temperature increased to 1450°C, the liquid spread completely on the TiB2 surface. In the contact melting process, several areas formed: titanium diboride area, Ni3B and TiB area, Ni and TiB area, and pure nickel. The systems were eutectic and their quasibinary phase diagrams had a eutectic at ~9% TiB2 with a melting point of ~1200°C at the Ni–TiB2 section and a melting point of ~1180°C at the (Ni–20% Cr)–TiB2 section. The alloys in the hypoeutectic part of the phase diagram consisted of the Ni, Ni3B, and TiB phases and additionally of the Cr2B phase in the (Ni–20% Cr)–TiB2 system. In the hypereutectic part of the phase diagram, the metal component disappeared and unreacted TiB2 additionally appeared in the (Ni–20% Cr)–TiB2 system. Zero solid-phase interaction and contact melting observed at temperatures of 1200 and 1180°C, which were significantly lower than the melting points of the interacting components (Ni, Ni–Cr), promoted favorable conditions for the use of nickel as a metal component in wear-resistant composites produced from granular titanium diboride, capable of operating under dynamic and shock loads at elevated temperatures (~900°C) and in corrosive environments. [ABSTRACT FROM AUTHOR] more...

Spark plasma sintering (SPS) is a type of pulsed electric current-assisted sintering technique. This method allows for rapid consolidation of powder materials into dense bulk when simultaneously applying uniaxial pressure and pulsed electrical current in a vacuum or protective atmosphere. Many scholars and researchers have realized the importance of the SPS due to its significant advantages in controlling the powder surface condition, atomic diffusion, phase stability, and crystal growth behavior. All these features inevitably influence the densification behavior and resulting physical and mechanical properties of the sintered materials. This review represents an extensive introduction of recent developments and fundamental principles in SPS techniques after a general description of the method and its outstanding advantages. A possible design for the SPS technique is proposed as well. Subsequently, the effects of each operating parameter, including current, voltage, and uniaxial pressure, on the densification behavior of advanced metals and alloys under various sintering conditions are reviewed. Finally, the successful applications of the SPS in preparing novel metal structural materials, such as high-quality special steels, new lightweight alloy materials with high performance, high entropy alloys, and other metal alloys, are described in detail. [ABSTRACT FROM AUTHOR] more...

The time dependence of densification for a zirconium diboride powder during the isothermal sintering in vacuum assisted with applied pressure varying from 12 to 60 MPa in the range 2110– 2300°C and the nonisothermal pressure sintering with temperature being constantly increased by 20 and 40°C/min was studied experimentally. The densification kinetics was analyzed within the framework of continuum theory for bulk viscous flow taking the powder particle shape influenced the rheological properties of porous bodies into account. The densification kinetics was represented by equations describing nonlinear steady-state creep of the matrix forming a porous body. In isothermal sintering conditions, the root-mean-square strain rate is proportional to the fourth exponent of the root-mean-square stress. The creep is controlled by the dislocation climb mechanism with an estimated activation energy that is equal to 626 kJ/mol and is consistent with the activation energy for self-diffusion of atoms in the metal sublattice of borides. The estimated Laplace pressure is virtually comparable with the average applied pressure. The root-mean-square shear stress induced by additive pressure decreases with increase in the relative density and approaches zero at neartheoretical density of the material. The root-mean-square strain rate sharply decreases in the isothermal sintering process and increases reaching the maximum on the nonisothermal sintering curve. Two temperature ranges with different activation energies were found for nonisothermal pressure sintering. The higher temperature range is characterized by energies that are significantly greater than those for isothermal sintering and is indicative of endothermic process. The estimated critical cold brittleness temperature for zirconium diboride to transform to plastic condition is 1345°C. [ABSTRACT FROM AUTHOR] more...

The effect of preliminary mechanical activation on the structural and physical state of the starting reagents, phase formation, and structure of sintered 80 vol.% ZrB2–15 vol.% SiC–5 vol.% B4C ceramics was studied. The starting powders were mechanically activated in steel drums of an AIR water-cooled high-energy ball mill at a rotation speed of 1440 rpm in an argon atmosphere. The mechanical activation lasted 15, 30, 60, and 120 min. The samples were produced by hot pressing using an SPD-120 pilot plant with induction heating in graphite dies in a CO–CO2 atmosphere. The particle-size distribution was determined by laser diffraction. Metallographic studies were conducted using a Superprobe 733 electron microscope (Japan). The mechanical activation of ultrahigh-temperature ceramics was found to influence the compaction kinetics of the samples. When mechanical activation time increased from 15 to 120 min, the sample density increased by 10% in the hot pressing process at 2150°C (15 min). The samples had 5–10 μm particles. During hot pressing, the ZrB2 matrix phase acquired a skeletal structure: the SiC phase in an amount of 15 vol.% acted as reinforcement in partial dissociation and B4C in an amount of 5 vol.% acted as a boron and carbon donor. Preliminary mechanical activation of the 80 vol.% ZrB2–15 vol.% SiC–5 vol.% B4C powder mixture intensified sintering in the temperature range 2100–2150°C, featuring the formation of secondary phases and recrystallization (at 2150°C), and promoted high density and low porosity of the hot-pressed ceramics. The studies showed that the densest samples were sintered from the powder mixture mechanically activated for 120 min. The density of the samples hot-pressed at 2100°C (5 min) and 2150°C (15 min) increased. [ABSTRACT FROM AUTHOR] more...

Powder metallurgy confers the specific properties to the materials by selecting appropriate components with proper compositions. An attempt was made to produce the dense aluminum-based metal matrix composite for the brake lining through powder metallurgy. In this work, two different sintering approaches of microwave sintering and spark plasma sintering were used to obtain the dense material. Based on the properties required for performing the intended functions, the powders of aluminum (80%), boron carbide (8%), silicon dioxide (7%), nickel (3%), and graphite (2%) were used to produce a metal matrix composite (MMC). The particle size, bulk/apparent density, and tap density of each powder were determined using the corresponding tests. The powders were mixed and blended with the help of a high-energy ball mill. The portion of the blended mixture was processed through the microwave sintering, where it was first compacted with the hydraulic press and then sintered at an appropriate sintering cycle. Other samples of the same chemical composition have been prepared using spark plasma sintering, where compaction and sintering occur simultaneously at a particular temperature and pressure. The density and microhardness values from each sample were determined using the Archimedes principle and the Vickers microhardness test, respectively. The SEM analysis was performed to analyze the morphology of the sample material after it has been processed by microwave sintering and spark plasma sintering. From the assessment of the obtained results, it was observed that the spark plasma sintering approach is an appropriate method to produce dense materials. [ABSTRACT FROM AUTHOR] more...

The paper describes developments of the Powder Metallurgy Institute (National Academy of Sciences of Belarus) in the field of producing two-layer permeable structures with a filtering layer 0.3-0.4 mm in thickness. The presented processes include: copressing of coarse powder and fine powder applied onto one of the shape elements with the help of binder; activation of sintering of fine metal fibers by fine powder particles; use of removable agents in plasma-assisted ion sputtering of coatings onto a porous powder substrate; self-propagating high-temperature synthesis in two-layer porous structures formed by different metals; and granulation of metal particles by pore agents. Examples of products made of the developed materials are provided. [ABSTRACT FROM AUTHOR] more...

The paper examines the structural and phase transformations in Fe-Al powders after mechanochemical sintering followed by heat treatment. The intermetallics are sintered through a series of successive stages, each resulting in a nanosized product. The amount of energy required for the formation of a single-phase intermetallic compound increases with aluminum content of the intermetallic phase (from FeAl to FeAl and then to FeAl). [ABSTRACT FROM AUTHOR] more...

The paper analyzes the sintering of three types of calcium phosphate powders and S-B-Na glass powder under the same conditions. It is concluded that a liquid phase, represented by the glass melt, shows up when the glass is sintered with biogenic or synthetic hydroxyapatite or a mixture of synthetic phosphates. The substantial pore formation in the sintering process is mainly due to the removal of carbon oxides and water vapors resulting from glass charge decomposition and glass boiling. Parameters of grain and porous microstructures of the ceramics are shown before and after the primary and secondary sintering. The mechanical strength and biosolubility of the ceramic samples are reported as well. [ABSTRACT FROM AUTHOR] more...

The paper summarizes and analyzes the known literature and data obtained by the authors on the development, use, and evolution of methods for nonoxidation sintering and chemical/thermal treatment of powders without protective gas environments. The efficiency of the method, including that for sintering of materials with high affinity to oxygen, is shown. [ABSTRACT FROM AUTHOR] more...

The paper examines the potential for increasing the corrosion resistance of composite electrolytic and galvanophoretic coatings under thermal treatment. The corrosion behavior of the coatings in a 3% NaCl solution is analyzed under various conditions of thermal treatment. It is established that thermal treatment of composite electrolytic Ni-B and Ni-Ti coatings has no effect on the corrosion resistance of the electrolytic coating itself or that placed on a substrate. At the same time, the galvanophoretic Ni-B-MoC coating shows high corrosion resistance after thermal treatment at 1100°C owing to the obliteration of porosity during liquid-phase sintering. [ABSTRACT FROM AUTHOR] more...

In the manufacture of sintered steels by metal injection molding (MIM), typical microstructural defects, such as pores and pore agglomerates, phase structure heterogeneities, and boundaries between different phases, are hard to avoid. Such heterogeneities cause crack origination, growth, and propagation when sintered materials are subjected to mechanical loads. The crack propagation path and fracture resistance are associated with the complex heterogeneous structure including ferrites, cementites, martensites, pores, and weak interfaces. With increasing sintering times, metal grains grow rapidly, leading to brittle fracture of the samples. Subsequent heat treatment substantially decreases the grain size and changes brittle fracture to ductile one. Multicycle sintering of the Catamold 8740 low-alloy steel greatly increases the impact strength of V-notched samples (from 7.55 to 13.95 J/cm2). Greater density of the samples and fewer stress concentrators favorably influence the material's capability to withstand impact loads. Thus when density of the billets following six sintering cycles increases by 2.5%, their impact strength becomes 1.8 times higher. With a greater number of sintering cycles, the ductile dimples become significantly larger, while the increase in shock impact and density of the sintered material gradually slows down. The grain size substantially increases (in turn, suppressing pore healing) and density of the samples becomes greater over the total sintering time. X-ray diffraction and spectral analysis revealed additional phases after sintering and heat treatment. Additional fine-crystalline carbide and oxide phases become more distinguished with further increase in the sintering temperature and heat treatment. Brittle inclusions, along with residual porosity, present in sintered steel decrease the dynamic properties of the material. [ABSTRACT FROM AUTHOR] more...

The article aimed to obtain a structural material with increased plasticity and density of 98.5–99.5% based on (Mo–25% W)–20 vol.% Cu pseudoalloys with a homogeneous refractory skeleton obtained by a single-time pressing and sintering of the dispersed mixture at temperatures 1400–1500°C. The production of a dispersed granulated Mo–25% W alloy with a powder particle size of 0.1–0.3 μm through the decomposition of complex ammonium paramolybdate and paratungstate salts into oxide compounds xWO3 · yMoO3 with their subsequent reduction by hydrogen in a rotary chamber was studied. Considering the temperature and decomposition time of complex salts in the moving layers, the physical and technological properties (such as phase composition, oxygen content, specific surface, bulk density, and tap density) of complex oxide powders xWO3 · yMoO3 and metal Mo– 25% W powders after reduction by hydrogen were compared with the corresponding properties of powders obtained in a stationary tube furnace in fixed layers. Temperature dependencies of porosity in (Mo–25% W)–20 vol.% Cu pseudoalloys after sintering at the temperature between 900 and 1500°C has been examined. It has been established that compaction of dispersed powder mixtures of (Mo–25% W)–20 vol.% Cu and homogenization of Mo–25% W alloy after sintering begin at the temperature 300°C lower than when sintering mechanical mixtures of commercial metal powders. It has been shown that (Mo–25% W)–20 vol.% Cu pseudoalloys obtained by liquid-phase sintering at 1500°C for 1 hour have the following characteristics: at 20°C, the ultimate tensile strength σt == 490 MPa, relative elongation δ = 1.1, Brinell hardness HB = 3.3 GPa, and at 500°C— σt == 370 MPa, δ = 4.4, and HB = 2.7 GPa. [ABSTRACT FROM AUTHOR] more...

The hand forging of cylindrical powder pellets of small weight (8.0–8.5 g), pressed at 700 MPa from mixtures of iron and graphite powders, was studied. The pre-sintered pellets were heated in charcoal at 1100°C and subjected to double-ended face forging on a heated flat anvil with a hammer with a flat striker and naturally cooled on a steel plate. The vertical setting of the forged pellets was 70-80%. The pellets were cut into samples for analysis. The influence of the graphite content on the compaction process and the mechanical properties of powder materials during hot free face forging have been established. The improvement in the properties of materials with a high graphite content (4 and 12%) was shown to be due to an increase in the number of sections for hot welding of iron grains. It is associated with shear deformation of the pellet material during free forging, contributing to the emergence of new iron–iron contacts. The high characteristics of materials containing 1.7% graphite are due to the action of several mechanisms in parallel: the dissolution of carbon in iron, decrease in total porosity, elimination of interparticle gaps, and grain refinement under shear deformation. The use of a steel shell makes it possible to significantly expand the range of powders and powder composites without rupture of the pellets in hot forging. The combination of experimental results and analytical data allowed us to conclude that hand forging was promising for a quick and cheap screening of formulations for dense powder materials. [ABSTRACT FROM AUTHOR] more...

The properties of sintered and heat-treated steels produced from the Catamold 8740 material by powder injection molding were examined. Parts made of the Catamold 8740 low-alloy mild carbon steel are used in the military, automotive, and other industries where high reliability and resistance to dynamic loads are required. The Catamold 8740 chemical homogeneity was studied as a function of powder injection molding parameters: heating rate, sintering temperature, holding time, and subsequent heat treatment. Microscopic analysis showed that Catamold 8740 was a mechanical mixture of powders in various sizes (carbonyl iron, nickel, Fe–Mo, Fe–Cr, Fe–Si-Mo, Fe–Si). When the heating rate of the Catamold 8740 powder mixture increased from 2 to 5 °C/min, the microstructural heterogeneity caused by uneven compaction decreased and the alloy formation process activated at 900–1340°C. The impact strength of Charpy V-notch test samples changed from 10.39 to 11.52 J/cm2 with higher sintering temperature and heating rate increasing from 2 °C/min (1270°C) to 5 °C/min (1340°C). When holding time increased from 30 to 90 min at a sintering temperature of 1340°C, the material became denser, the pores rounded, and the ferrite matrix homogeneous. However, the impact strength decreased by a factor of 1.4 because of coarser grain sizes and brittle fracture. Heat treatment processes reduced the impact strength after sintering. The results obtained were used to optimize the powder injection molding parameters. The influence of chemical and dimensional inhomogeneity of the starting Catamold 8740 powders and sintering kinetics on the structure and mechanical properties of parts operating under impact loads was established. [ABSTRACT FROM AUTHOR] more...

Abstract  The paper examines the densification kinetics in liquid-phase sintering of Mo-Ni-Sn samples containing 90 wt.% of molybdenum and 10 wt.% of liquid phase in which the content of nickel varies from 5 to 67.5 wt.%. The samples continuously densify with increasing nickel content. It is examined how the amount of the 28 wt.% Ni-72 wt.% Sn liquid phase influences the densification kinetics of samples with varying content of molybdenum. The densification parameter increases with the amount of the liquid phase. [ABSTRACT FROM AUTHOR] more...

Abstract  The paper examines how the amount of the liquid phase influences the densification of loose W-Cu and Mo-Cu powder mixtures in liquid-phase sintering at 1200°C, with the content of the low-melting component ranging from 20 to 90 wt.%. It is observed that the density grows continuously with increasing amount of the liquid phase in both W-Cu and Mo-Cu systems. It is shown that samples sintered with a great amount of the liquid phase in the W-Cu and Mo-Cu systems retain their shape. [ABSTRACT FROM AUTHOR] more...

In this paper, the results of numerical and experimental studies concerning the effect of mediumfrequency induction sintering of Fe-3 wt.% Cu powder metal (PM) compacts are discussed. Several sintering durations from 30 to 180 sec are studied. The mixed powders are compacted at 600 MPa and sintered by medium-frequency induction system (30-50 kHz frequency and 12 kW power). Magnetic and thermal analysis, mechanical properties, and densities of copper-iron PM compacts are presented. [ABSTRACT FROM AUTHOR] more...

The paper examines the influence of sintering temperature in the range 1150-1300°C on interaction of chromium carbide CrC and a Kh13M2 steel matrix. It is shown that molybdenum actively participates in the interaction process, which leads to the formation of MC, MC, and MC carbides even at 1150°C. [ABSTRACT FROM AUTHOR] more...

The paper describes a new process of producing structural steel parts by molding mixtures of iron and iron oxide powders with a binder, reducing the oxides in vacuum with nanosized products from pyrolysis of the binder, and sintering. It is shown that this process has advantages over conventional pressing and sintering as well as the MIM process: it allows parts of complex shape to be produced and the cost of products to be decreased. [ABSTRACT FROM AUTHOR] more...

The paper studies the density and porosity of 44NKhTYu elinvar alloy blanks produced by powder technology, jet molding, and electron-beam remelting. It is shown that jet molding and solid-phase sintering of powders over a narrow remelting temperature range are the most promising. They can be used to make blanks and products whose density and porosity are close to those of cast alloy, the metallic yield being increased. [ABSTRACT FROM AUTHOR] more...

The paper examines the effect of temperature and volume fraction of refractory particles on the kinetics of their growth during liquid-phase sintering of Cr-Cu composites in the temperature range 1150-1350°C under a vacuum of (2-4)∙10 Pa. It is established that the growth kinetics of average-size particles is described by a near-cubic law and the decrease in their number is determined by a near-inverse dependence: the apparent activation energy (Q = 113 ± 10 kJ/mol) is of the order of magnitude comparable to that of diffusion in liquid metals. According to the Lifshitz-Slyozov-Wagner theory (LSW theory), diffusion coalescence is indicative of diffusion-controlled particle growth. Experimental growth constants are one order of magnitude higher than those calculated within the classical LSW theory. The increase in the growth rate constant with volume fraction of refractory particles varying from 0.4 to 0.7 and the change in the particle size distribution function after sintering for 90 min at 1200°C agree with the Ardell model, which modifies the LSW theory considering the effect of volume fraction of particles on their growth kinetics. [ABSTRACT FROM AUTHOR] more...

The paper presents an analytical review of published data and the authors' data on the use of incompletely sealed steel containers for the sintering of iron-powder products in air. Consideration is given to additional techniques for removing oxidation products during sintering such as introduction of protective gas microgenerators into containers or use of a fill. It is concluded that it is reasonable and possible to sinter small and medium batches of powder products and to remelt powder waste at existing thermal stations. [ABSTRACT FROM AUTHOR] more...

The interaction of hafnium boride and chromium in the HfB2–Cr system is studied. Solid-phase interaction occurs at temperatures up to 1650 ± 30°C to form chromium boride (Crubscript>2B) on the chromium side of the HfB2–Cr system. The diffusion of boron from hafnium diboride to chromium is the control link of this interaction process. At 1650 ± 30°C, a liquid phase of eutectic composition with a contact angle on hafnium diboride of 20° shows up in the reaction area. The interaction proceeds with the dissolution of each contacting element in the eutectic, equalizing their concentrations through liquid-phase diffusion. The eutectic nature of the quasibinary HfB2–Cr phase diagram, a small contact angle formed by the eutectic on hafnium diboride, decreasing with higher temperature, and high chromium vapor pressure, promoting uniform chromium distribution over the entire charge through the vapor phase allow chromium to be considered a promising addition that activates the sintering of hafnium diboride. [ABSTRACT FROM AUTHOR] more...

The paper presents a brief literature review on microstructure development in composites during liquid-phase sintering. Two mechanisms of microstructure coarsening in liquid-phase sintered systems are considered: dissolution-reprecipitation and coalescence. The data are systematized in the context of the Lifshitz-Slyozov-Wagner theory and the theory of coalescence at the final stages of liquid-phase sintering. The effect of various physicochemical factors, such as temperature, volume fraction, and time on microstructure development is explained in terms of quasichemical kinetics. [ABSTRACT FROM AUTHOR] more...

The paper examines the micrononuniform distribution of temperature and its influence on the rheological behavior of a copper powder with oxidized spherical particles as an effective dispersion-porous medium through which an electric current is passed. The micrononuniform distribution of temperature needs to be considered to describe the temperature dependence of the rheological behavior of effective dispersion-porous medium during resistance heating. [ABSTRACT FROM AUTHOR] more...

The paper examines the dependence of the secondary microstructure and electromagnetic parameters on the heat-treatment conditions of ferrite elements in the Mg-Mn-Zn-Ca-Fe-O system used in switching and logic elements. An optical microscope revealed dotted and netted secondary microstructures. The dotted structure is found in the samples sintered at 1603 K, quenched at 1273 K, and additionally annealed at 823 K. It is shown that annealing for up to 3 h increases the coercivity H, without degradation of the other parameters. This made it possible to increase the cyield of elements by a factor of 1.5 by increasing the H of rejected (because of low coercivity) elements. We developed a technique that provides equal temperature-time conditions for all annealed samples in a lot and allows controlling the yield of elements by periodically adjusting the annealing duration based on inspection of samples from inspection lots. [ABSTRACT FROM AUTHOR] more...