Powder Metallurgy and Metal Ceramics (v.56, #11-12)

Effect of Attrition Milling on Lithium-Ion Conductors by Xiaojuan Lu; Fengli Meng; Liyue Wang; Huaqing Zhu; Haihui Li (611-616).
Lithium lanthanum titanate Li0.33La0.56TiO3 with a perovskite structure and Li1.3Al0.3Ti1.7(PO4)3 with a NASICON structure are promising solid lithium-ion conductors. Attrition milling is carried out to alter the particle size and a solid-state reaction method is used to prepare the pellets. The mean volume of Li1.3Al0.3Ti1.7(PO4)3 and Li0.33La0.56TiO3 tends to increase and to decrease, respectively, with increasing attrition milling time, which is due to the different hardness of the starting materials used. When pressed into pellets, the powders with smaller variation in the particle size possess denser packing and, therefore, higher conductivity. The conductivities of lithium–conductors are in strong correlation with the size of the starting powders and the density of the pellets.
Keywords: lithium–ion conductor; attrition milling; morphology; particle size

The present study discusses the microstructure properties of Al–SiC composites. Certain deformation processes such as reciprocating extrusion (RE) were found to be applicable to strengthen the metal matrix composites (MMCs) and to refine the grains of the matrix. In line with this argument, reciprocating extrusions were implemented by applying up to five passes. The RE process was employed in fabricating a homogenous dispersion of SiCp and a fine-grain composite structure. The composites in question were studied in terms of their behaviors and microstructures on the basis of the RE process.
Keywords: extrusion; grain size; microstructure; metal matrix composites; reciprocating extrusion

Spark Plasma Sintering of TiN (Shell)–Si3N4 (Nanofiber) System by O. B. Zgalat-Lozynskyy; N. I. Tischenko; A. V. Ragulya (625-632).
The formation of nanocomposite powder mixtures in titanium nitride–silicon nitride system is investigated. Titanium nitride coating (<20 nm thick) is obtained on the surface of silicon nitride nanofibers by chemical synthesis. A comparative analysis of consolidation by spark plasma sintering of nanocomposite materials prepared by chemical synthesis and mechanical mixing is conducted. After spark plasma sintering, core–shell configurated composites demonstrate a homogeneous fine-grained structure with particles 50–150 nm in size and high mechanical properties (HV ≈ 22 GPa, K Ic ≈ 6.4 MPa · m1/2).
Keywords: nanofibers; nanocomposite; nanopowders; spark plasma sintering; Si3N4 ; TiN

The phase composition and structurization of three types of copper and molybdenum composite materials, 0.8 to 5 mm thick, which were condensed from the vapor phase at substrate temperatures 700 and 900°C, are considered: precipitation-strengthened composites, microlayered composites with alternating copper and molybdenum layers 1 to 10 μm thick, and bulk nanocrystalline composites with alternating layers thinner than 0.5 μm. Standard precipitation-strengthened Cu- and Mo-based materials condensed from the vapor phase at substrate temperatures 700–900°C can be produced over a relatively narrow composition range of the strengthening phase (0.1–3 wt.% Mo). When Mo content is 3–5 wt.%, the molybdenum particles change their shape from round to acicular and become discontinuous chains oriented perpendicularly to the vapor flow. If there is more than 5 wt.% of the second phase, the condensed composite materials (CCMs) show a layered structure. The layered structure can be observed in other CCM types (Cu–W, Cu–Cr, NiCrAlTi–Al2O3). Layered copper and molybdenum CCMs, 6 mm thick, produced on a rotating substrate heated to 700 ± 30°C have been experimentally confirmed to belong to bulk nanocrystalline materials.
Keywords: high-speed evaporation–condensation; copper; molybdenum; vacuum; precipitation-strengthened materials; layered materials; bulk materials

In this research, AlSi10Mg composites reinforced with graphene nanoplatelets (GNPs) were fabricated in order to study the effect of GNPs on microstructure and mechanical properties of the AlSi10Mg alloy. The composites were produced by a wet mixing method followed by two-step hot consolidation (hot compaction then hot extrusion) at 673 K (400°C). The weight percentages of GNPs were 0.5 and 1 wt.% with respect to the AlSi10Mg alloy. Tensile and Vickers hardness tests at room temperature were performed to evaluate the effect of GNPs on mechanical properties of asfabricated composite. The outcomes show that the high quantity of GNPs (>0.5 wt.%) deteriorates the mechanical properties of AlSi10Mg composite due to the agglomeration of GNPs and, as a consequence, introduction of internal porosity in the composite. However, it is found that relatively low fraction of GNPs can uniformly be dispersed in the Al alloy matrix through the wet mixing method. The hardness and tensile results demonstrated that the mechanical properties improve slightly through the addition of 0.5 wt.% of GNPs, while 1.0 wt.% GNPs addition did not lead to improved performance owing to overwhelming effects of porosity.
Keywords: metal matrix composite; hot consolidation; graphene; mechanical properties; microstructure

Structure, Mechanical and Tribotechnical Properties of Glass-to-Metal Composites Based on Iron–Carbon Alloys by G. A. Baglyuk; V. Ya. Kurovskii; O. D. Kostenko; G. A. Maksymova; G. M. Molchanovska (656-663).
Principle mechanical and tribotechnical properties of glass-to-metal iron–carbon alloys with 5% glass modified with boron carbide, copper, and boron nitride additives are investigated. It is shown that the introduction of 2% boron carbide in the starting powder mixture provides a significant increase in the wear resistance and friction coefficient (0.27–0.42), compared to B4C-free materials. The use of hot pressing promotes a sharp increase in the wear resistance, compared to sintered materials, and hardly affects the friction coefficient. The microstructure of glass-to-metal sintered materials has a distinct heterophase character and consists of metal matrix phase based on at least three types of grains (boron–cementite Fe3(B0,7C0,3), lamellar and granular pearlite) and a glass phase, which is distributed in the steel matrix in the form of either thin layer at intergranular boundaries or separate inclusions of irregular shape up to 30–50 μm in size.
Keywords: glass-to-metal composite; sintering; hot pressing; boron carbide; wear; friction coefficient

Properties of ZhS32-VI Powder Alloys with Titanium Carbide by G. P. Dmitrieva; T. S. Cherepova; A. I. Dukhota; V. I. Nichiporenko (664-669).
To design a wear-resistant material operated at high temperatures, the physical and mechanical properties of the new nickel alloy (whose components are heat-resistant alloy ZhS32-VI and 30–50% titanium carbide) obtained by powder metallurgy are investigated. It is shown that the temperature where the alloy starts melting is 1360 ± 10°C, the wear resistance at <1050°C doubles that of nickel-based powder alloys with titanium carbide, while the heat resistance at 1100°C satisfies the requirements of the intended alloys. It is shown that the obtained alloy can be plasma-sprayed onto the blade material and used for protecting the contacting surfaces of GTE blades against wear.
Keywords: powder alloys; ZhS32-VI; titanium carbide; wear resistance; heat resistance; melting temperature

Permeability is one of the key properties for understanding the fluid flow and pressure drop in porous metal. In this study, a novel 304 stainless steel fiber reinforced powder metallurgy (P/M) material is produced. Stainless steel powders and short fibers are alternately laid in layers according to mass fraction and then sintered to produce the porous material. Air and water permeability tests are conducted to characterize the permeability of the material. The powder mesh, porosity, and pore size are varied to investigate the effect of permeability. Porous molds made of the material are designed to perform paperboard molding and plastic-injection experiments. The results demonstrate that the relationship between pressure drop per unit length and flow velocity is a parabola, where air or water flows through the P/M material. The permeability coefficient decreases with increasing powder mesh. Compared to water going through the material, the permeability coefficient is higher and the inertial loss is more significant in case of air. The pore size has greater effect on the permeability, than porosity. The perfect appearance of the paperboard presents a good permeability of the P/M material, showing the promising application in molding.
Keywords: powder metallurgy material; permeability; inertial loss; pore size; porosity

Effect of Chromium Diboride Additives on Strength Properties of NiAl–CrB2 Composites in a Wide Temperature Range by O. P. Umanskyi; M. P. Brodnikovskyi; M. S. Ukrainets; O. M. Poliarus; O. U. Stelmakh; D. M. Brodnikovskyi (681-687).
The compressive yield stress and bending strength of NiAl–CrB2 composites are studied in the 20–800°C temperature range. The effect of the composite phase ratio and experimental temperature on the composite strength for different loading patterns is established. During tensile stresses, the introduction of 15 wt.% CrB2 into the intermetallic is optimal to ensure the maximum bending strength of the composite at 500°C. The bending strength of NiAl–15 wt.% CrB2 composite at the experimental temperature 500°C exceeds that of the starting NiAl, by a factor of 3.
Keywords: NiAl; CrB2 ; high-temperature strength; bending strength; yield point; composite material; dispersion strengthening

Quality Analysis of Aluminized Surface Layers Produced by Electrospark Deposition by G. V. Kirik; O. P. Gaponova; V. B. Tarelnyk; O. M. Myslyvchenko; B. Antoszewski (688-696).
The structurization of aluminum coatings on steel 20 and 40 substrates produced in different ESD modes is considered. The thickness and microhardness of ‘white’ and transition layers and the surface roughness increase and chemical and phase compositions change with higher discharge energy. The coating formed at low discharge energies mainly consists of α-Fe and aluminum oxides. Electron microprobe analysis shows that the coating produced at high discharge energies consists of iron and aluminum intermetallics and free aluminum. Compared to steel 20, the electrospark-deposited coating on steel 40 has a deeper layer with increased hardness and has greater microhardness. The surface roughness remains virtually the same. To decease roughness and increase integrity of the coatings, we recommend electrospark deposition with the same electrode (aluminum), but at lower discharge energies (W d = 0.52 J).
Keywords: electrospark alloying; aluminizing; microstructure; coating; surface; X-ray diffraction; electron microprobe analysis; microhardness; surface roughness

High-Temperature Enthalpy of La2Hf2O7 in the Temperature Range 490–2120 K by A. R. Kopan; N. P. Gorbachuk; S. M. Lakiza; Ya. S. Tishchenko (697-706).
Lanthanum hafnate La2Hf2O7 was produced chemically by inverse precipitation from ammonia solution and a mixture of La and Hf nitrates, followed by hydroxide decomposition at 1250°C in air and melting of the oxide mixture in a solar furnace. The formation of La2Hf2O7 was ascertained by X-ray diffraction. The La2Hf2O7 enthalpy increment was measured in the range 490–2120 K (for the first time in the temperature ranges 490–988 K and 1740–2120 K) by drop calorimetry using a Setaram HT-1500 high-temperature differential calorimeter and a high-temperature calorimetric device. A fitted equation for the enthalpy increment was used to calculate the main thermodynamic functions (heat capacity, entropy, and Gibbs energy) in the temperature range 298–2120 K. The experimental results are compared with the published data and those assessed using the Neumann–Kopp rule.
Keywords: calorimetry; enthalpy; heat capacity; entropy; reduced Gibbs energy; lanthanum hafnate

Electrochemical Corrosion Behavior of Air-Exposed Zr–Mn–Cr–Ni–V Alloy by Yu. M. Solonin; O. Z. Galiy; A. V. Samelyuk; L. O. Romanova; K. A. Graivoronskaya (707-717).
Scanning electron microscopy and electron microprobe analysis show that the ZrMnCrNiV alloy has a dendritic structure and is chemically inhomogeneous. The corrosion mechanism for the unexposed alloy and the alloy exposed in air for 7 and 15 days, followed by aging in a 30% KOH solution, is the same: corrosion originates at the interphase boundary and propagates along it, which is typical of pitting corrosion. If the alloy is preliminary exposed in air, its surface has a greater number of pittings, but all of them are smaller in area and depth, making the corrosion process more uniform. In hydrogenation–dehydrogenation of this alloy, even more uniform distribution of smaller corrosion areas is observed. Studies of the corrosion resistance of this alloy in a KOH solution carried out by atomic adsorption spectrometry show that the alloy powder exposed in air has higher corrosion resistance compared to the unexposed powder. Electrochemical corrosion studies of the alloy conducted in the anodic region using the method of polarization curves indicate that the corrosion rate for the unexposed and exposed alloys is controlled by the rate at which passivating films form. The most extensive passivation region is observed in the alloy exposed in air for 15 days. It shows adequate corrosion resistance in a 30% KOH solution. The cyclic resistance studies for the electrodes produced from the alloy powder exposed for 10 days, at a discharge to potential difference E = –1.0 V and E = –0.8 V, demonstrate that oxidation in the hydrogenation-dehydrogenation process affects the cyclic resistance. It is found that there is liming time for exposing the alloy in air (as an ingot and/or powder) after which the cyclic resistance deteriorates.
Keywords: Zr alloy; hydrogenation; air exposure

Effect of Shock Compression Conditions on the Production of Cubic Si3N4 by A. V. Kurdyumov; V. F. Britun; A. I. Danilenko; V. V. Yarosh (718-725).
The yield of cubic γ-Si3N4 phase depending on the shock compression pressure and temperature and on the type of starting modification (α or β) is studied. Pressure and temperature depend on the explosive power, shock-wave loading pattern, KCl content of the charge, and charge density. The yield of the γ-phase was determined by quantitative X-ray diffraction using calculated intensities of lines for each phase. The optimum conditions of shock compression to reach the maximum yield of the cubic phase were found (for specific explosives). It is concluded that the cubic phase forms from hexagonal modifications by the diffusion-controlled mechanism and that the α-phase is metastable.
Keywords: silicon nitride; shock compression; cylindrical recovery capsules; KCl addition; cubic Si3N4 ; phase transformation mechanism

Application of Domestic Heat-Resistant Powders in Additive Techniques by O. A. Glotka; O. V. Ovchinnikov; V. I. Degtyaryov; S. A. Kameneva (726-732).
The products produced using additive techniques (with no use of conventional production techniques) are of high priority for aerospace and aircraft engine building. The possibility of using domestic heat-resistant powders in additive processes is investigated. It is shown that domestic heat-resistant materials are promising for additive techniques. It is found out that domestic powders have a wide size range and the defects, such as satellites and chips, are detected on the powder granule surface. It is revealed that the surface morphology and microstructure of particles are typical for heat-resistant nickel alloys. It is established that heat-resistant nickel-based EP741p alloy (SE USSI) can be used in additive techniques.
Keywords: additive techniques; heat-resistant nickel-based material; flow rate of powder; morphology; microstructure