Powder Metallurgy and Metal Ceramics最新文献

The research was carried out to increase the added value of the basalt rock from East Lampung, Indonesia, by using it as a raw material for producing a glaze for earthenware ceramics. Basalt of scoria and basalt smelted at a temperature of 1,400°C mixed with local kaolin and feldspar from Lampung, Indonesia, with variations in the composition of basalt to kaolin and feldspar at 70 : 15 : 15, 50 : 25 : 25, and 30 : 35 : 35, respectively, was applied. The glazing process using the dip coating method was applied, followed by burning all samples at a temperature of 1,000°C. All samples were held for 8 hours at the specified temperature and cooled to room temperature. According to the results of determining the color properties of each sample it is determined that they depend on the iron content. It was established that the more of basalt in composition is used, the brighter the red color of the glaze becomes when crystallization grows due to the devitrification process during cooling. XRF analysis was conducted to determine the chemical composition of each composition to evaluate its effect on crystallization formed based on the XRD test. Furthermore, an SEM analysis was carried out to determine the topography and morphology of the glaze samples obtained. According to the analysis results, the natural basalt samples provide a topography of a bright and well-adhesive layer. In contrast, molten basalt gives a rough and opaque surface. It has significantly different results as the starting phase of each material has various structure forms, which are influenced by the forming glaze surface at 1,000°C. At the 2000 SEM magnification, samples with basalt scoria as based material tend to fuse with the main body of earthenware. It gives the glazed coating strong adhesion to stick to the earthenware surface. At the same time, molten basalt provides cavities and pores in the area of interaction between the main body and the glazed surface. The growing use of raw and melted basalt in the glaze layer provides a brighter red gradation, and the majority of the phase that happened was from the pyroxenic group and some wollastonites.

The reactive synthesis of heterophase refractory ultrahard B₄C-based composites by spark plasma sintering (SPS) was examined. To produce heterophase B₄C + TiB₂ + CrB₂ ceramics, the chemical reaction between boron carbide and chromium oxide and between boron carbide and titanium carbide resulting in boron carbide–chromium diboride and boron carbide–titanium diboride composites was previously studied. The reactive sintering of B₄C + Cr₂O₃ + C and B₄C + TiC mixtures using boron carbide powders obtained from the Zaporizhzhya Abrasive Plant and Donetsk Chemical Reagent Plant (Ukraine) was compared. The boron carbide powders differed in the ratio of B₁₃C₂ and B₄C phases and particle sizes. The reactively synthesized TiB₂, CrB₂, and CrTiB₂ boride phases positively influenced the SPS consolidation and properties of the boron carbide composites. The B₄C–CrB₂ and B₄C–TiB₂ ceramics subjected to Vickers hardness testing under a load of 98 N showed HV levels of 23–29 GPa and 26–28 GPa. The ceramics demonstrated brittle fracture according to the Half-penny model, with a fracture toughness of 3 MPa∙m^1/2 for B₄C–CrB₂ and 4.4 MPa∙m^1/2 for B₄C–TiB₂. The 90 vol.% B₄C–5.5 vol.% TiCrB₂–4.5 vol.% C ceramics with ~33 GPa hardness and ~ 4 MPa∙m^1/2 fracture toughness were produced by reactive SPS from a mixture of B₄C (Zaporizhzhya Abrasive Plant), 6.6 wt.% TiC, and 11 wt.% Cr₂O₃. The high strength of TiCrB₂ ceramics was attributed to the stress–strain state, where the matrix phase of boron carbide was subjected to compressive stresses. The high hardness and fracture toughness allow the B₄C–TiCrB₂ composite to be classified as an ultrahard ceramic material.

Phase equilibria involving the stable high-temperature quaternary χ_Fe,Cr,Mo,C phase were established in the Fe–Mo–Cr–C phase diagram. The arc-melted alloys were annealed at subsolidus temperatures for 52 h and then quenched in liquid gallium. The solidus temperature of the alloys was determined with the Pirani–Alterthum method. High-temperature X-ray diffractometry was employed to monitor the sequence of changes in the alloy phase composition from room temperature to the solidus temperature. The χ + η + α, χ + η, and χ + σ phase equilibria were directly observed at 973 K < T < 1373 K, 1273 K < T < 1530 K, and 1523 K < T < 1530 K, respectively, in the Fe_52.5Mo_23.5Cr_18.7C_5.3 (at.%) alloy. The χ + M₂₃C₆ + α and χ + σ phase equilibria were directly observed at 973 K ≤ T < 1523 K and 1473 K < T < 1525 K in the Fe_55.5Mo_11.8Cr_28.2C_4.5 (at.%) alloy. It was shown that the two-phase χ + σ equilibrium could be preceded by three-phase χ + η + σ equilibria or a single-phase χ _Fe,Cr,Mo,C equilibrium region (for the Fe_52.5Mo_23.5Cr_18.7C_5.3 alloy in the 1523 K < T < 1530 K temperature range). The quaternary χ _Fe,Cr,Mo,C phase was found in the (51.9–64.9) Fe, (5.4–23.5) Mo, (14.5–35.4) Cr, and (1–10.7) C at.% composition ranges. Primary crystallization regions of the σ _Fe,Cr,Mo,C and α_Fe,Cr,Mo,C phases with solidus temperatures of approximately 1530 K (for the Fe_52.5Mo_23.5Cr_18.7C_5.3 alloy) and 1525 K (for the Fe_55.5Mo_11.8Cr_28.2C_4.5 alloy) were revealed. The linear thermal expansion coefficients for the χ _Fe,Cr,Mo,C, η _Fe,Cr,Mo,C, and α_Fe,Cr,Mo,C phases of different composition observed for different temperature ranges were determined.

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.

Changes in the porous structure of compacts produced from carbonyl iron and a mixture of iron with doping additions (4 wt.%) with increasing holding time at 900°C were analyzed. The compacts were sintered in a hydrogen atmosphere for 5, 10, 15, and 30 min. Powders of carbonyl iron, nickel, and ferroalloys (Fe–Si, Fe–Cr, Fe–Mo) were the starting materials. The structural parameters (characteristic pore size and radius of conditional particles) were evaluated from computer processing of electron microscopy images. The experimental studies found that the average characteristic pore size in the samples of carbonyl iron and those with doping additions changed differently during sintering, especially in the first minutes. The carbonyl iron samples had 2% higher porosity than that of the doped ones after 5 min of sintering but became 9.5% lower after 15 min. This can be explained by a significant change in the interaction between pores in the homogenization process in the samples with doping additions at the beginning of sintering. A stage with uneven pore filling resulting from local chemical inhomogeneity was revealed. To describe the metal component of the porous structure, the radius of conditional particles was chosen. This parameter increased 4.7 times faster for pure carbonyl iron than for doped carbonyl iron during sintering. The experimental studies showed that the relationship between the radius of conditional particles and the porosity of the samples was hyperbolic and determined by the size of the starting powders. The coefficients of this relationship, experimentally found for a material of specific chemical composition, can be used to describe the sintering of materials with similar chemical compositions.

Cu matrix composites have received increased attention in a wide industrial area because of their excellent mechanical properties and good electrical and thermal conductivity. However, the addition of general ceramic reinforcements often leads to a marked reduction in electrical conductivity for Cu matrix composites. In this study, the ZrB₂-reinforced Cu composites have been developed to overcome this drawback since these metal borides possess relatively high electrical conductivity. The 5 wt.% ZrB₂/Cu composites were prepared using hot-pressed sintering techniques at varying temperatures from 760 to 920°C. The influence of sintering temperature on the microstructure, relative density, and mechanical and electrical properties was examined. The results of the SEM observation show that ZrB₂ particles are seamlessly integrated into the Cu matrix for all ZrB₂/Cu composites. The average grain size of the Cu matrix increases from 360 to 980 nm with the increase of the sintering temperature. The increase in sintering temperature also leads to the surface porosity decrease from 1.4 to 0.4%. The relative density and electric conductivity of the composites increase at the same time as the sintering temperature increases. However, microhardness increases and decreases, with a maximum value of 92 HV0.2 achieved at 840°C. The elastic modulus and nanohardness maps determined from the nanoindentation indicate that the reinforced ZrB₂ particles demonstrate the highest values for elastic modulus (340–500 GPa) and nanohardness (30–48 GPa). At the same time, the Cu matrix possesses a modulus of 100–200 GPa and nanohardness of about 10 GPa. TEM observation confirmed that the sintering temperature exhibits little influence on the interface reaction between ZrB₂ and Cu. Both sharp interface and interface with amorphous transition layer are observed. The variation of microhardness is mainly due to the strengthening of grain refinement and to the mismatch of the thermal expansion coefficients. The above results can provide further insights into the deeper understanding of the role of sintering temperature during hot-pressed sintering.

Near-infrared long afterglow materials have the characteristics of non-obscuring bio autofluorescence and good photo/chemical stability. They can play an essential role in bioimaging, whereas LiGa₅O₈:Cr³⁺ has long afterglow and optical photoexcitation properties. In this paper, LiGa₅O₈:Cr³⁺ nanophosphors were successfully synthesized by hydrothermal method. X-ray diffraction (XRD) patterns were recorded using an X-ray diffractometer. Luminescence spectra and decay curves were obtained via a fluorescence spectrophotometer. The microstructural properties of the samples were analyzed using scanning electron microscopy (SEM). Transmission electron microscopy (TEM) images were recorded on a TEM instrument. Thermoluminescence spectrometer was employed to obtain a thermoluminescence curve. Using Tween 20 as the experimental chelating agent, it was found that the ratio of total metal ions to Tween 20 significantly affected the luminescence properties of LiGa₅O₈:Cr³⁺. When the ratio of total metal ions to Tween 20 was 7 : 1, the sample had less impurity phase, high crystallinity, regular grain shape, and a size of about 100 nm. The fluorescence spectra showed that the main excitation peaks were 410 nm and 608 nm, and the main emission peaks were 720 nm. The sample with a ratio of 7 : 1 had a higher relative intensity than all other samples, with more effective traps and greater stored energy to produce more luminescent carriers. The kinetic order at this point was 2. It provides a solid basis for bioimaging.

The influence of particulate reinforcements produced from an 85 wt.% Ti + 15 wt.% Al powder mixture, processed through high-voltage electric discharges (HVED) in kerosene, on the key mechanical properties of a polymer composite with an ED-20 epoxy oligomer matrix was studied. Following HVED processing, the powder showed the following phase composition: 74 wt.% Ti, 15 wt.% Al, and 11 wt.% TiC, with an average particle size of 10–12 μm. The reinforcement content of the composite varied from 0.25 to 2.0 wt.%. The optimal reinforcement content that substantially improved the strength and impact toughness of the composite (by 1.7–1.8 times compared to the starting matrix) was found to be 0.5 wt.%. When the particulate reinforcement content in the composite was raised to 1.25–2.0%, the fracture strength reduced significantly, nearly reaching the level of the starting epoxy matrix. A model was proposed to account for the extremum observed in the dependences of the mechanical properties on the reinforcement content of the composite. The model relied on the hypothesis that mechanical and structural factors independently influenced the properties of the composite. The mechanical effect was determined by the redistribution of strain-induced stresses between the matrix and reinforcement and by the adhesion between the composite components. The structural effect resulted from changes in the properties of the polymer matrix induced by surface interactions with the reinforcement particles.

The effect of niobium on the structure, phase composition, and mechanical properties of γ -TiAl alloys were studied. The γ-TiAl alloys were doped with niobium within a solid solution; the amount of niobium in the alloys ranged from 2 to 10 at.%. Niobium was introduced as an Al3Nb intermetallic, allowing a superfine powder mixture to be produced by high-energy grinding. A TiH₂ + Al₃Ti + Al₃Nb powder mixture was used to prepare the γ -TiAl alloys. This route minimized the Kirkendall–Frenkel effect in the Ti–Al system and prevented increase in additional porosity during sintering. Only TiAl and Ti₃Al phases were revealed in the sintered materials, indicating that niobium had dissolved in the existing phases. To achieve the desired phase composition in the alloy, the content of aluminum had to be increased to compensate for its partial loss through evaporation during sintering. The alloys with a lower aluminum content showed higher strength but lower ductility, both at room and elevated temperatures, because of a greater amount of the α₂ phase. Niobium doping reduced sintering shrinkage by 2–4% and inhibited the grain growth. The material with a low niobium content had greater strength and ductility at a sintering temperature of 1200°C, when the grain size hardly changed. The grain growth was inhibited by niobium doping at a high sintering temperature of 1400°C. The yield stress increased with the niobium content. The studied alloys exhibited satisfactory low-temperature strength and ductility, as well as high creep resistance at 700°C. They showed a little tendency to weakening and are therefore promising for hightemperature applications above 700°C.

The mechanical behavior of Al₆₃Cu₂₅Fe₁₂ quasicrystalline coatings in the temperature range of 77–1073 K was studied by the microindentation method. Coatings with a thickness of 350 μm were obtained on the substrate of steel 45 by high-speed air-fuel spraying of water-atomized powders with a size fraction of 40–80 μm. The content of the icosahedral quasicrystalline phase in the coatings after production was 75 wt.%. Annealing at 998 K for 20 min made it possible to obtain 100% of the quasicrystalline phase in the coating. The microhardness of the studied coatings at a temperature of 77 K and room temperature (293 K) is ~7 GPa and slightly decreases to a level of ~4.5 GPa at a temperature of 725 K, followed by a sharp decrease to 1.5–1 GPa at 923–973 K. Analysis of the temperature dependence of the plasticity characteristic δ_H, determined by the indentation method, showed that up to a temperature of 873 K, the quasicrystalline coatings of the Al–Cu–Fe system have the brittleness during compression/tension tests, and above 873 K they start to possess a macroplasticity. Calculation of the value of δ_H in a wide temperature range makes it possible to predict the mechanical properties of brittle, at standard test methods, quasicrystalline coatings of the Al–Cu–Fe system.