Powder Metallurgy and Metal Ceramics (v.57, #3-4)

Ultrafine WC–Co composite powders are synthesized via spray conversion method. The effect of carbon source (organic carbon and carbon black) and atmosphere (H2 and N2) on the composite powders is investigated in terms of phase composition, particle size distribution, morphology, and carbon content, including the total carbon and free carbon using X-ray diffraction, particle size analyzer, scanning electron microscope, and infrared carbon and sulfur analyzer. The results show that using organic carbon or carbon black and H2 or N2 has its own advantages and disadvantages. Therefore, carbon source and the atmosphere can be chosen according to the application of the composite powders, i.e. cemented carbides and thermal spraying.
Keywords: WC–Co composite powders; spray conversion processing; reduction–carbonization; carbon source; atmosphere

Pressing of Long-Length Pellets From Titanium Hydride Powder by A. V. Minitsky; P. I. Loboda (138-143).
The paper examines pressing of the titanium hydride powder in a die lubricated with adipose to produce pellets with H/d ≈ 4/1 and additional compaction of these pellets with a combined lubricant separating them from the die. The pellet extrusion pressure in the additional compaction process is one order of magnitude lower than when the powder is pressed in a lubricated die. This is indicative of drastic decrease in the external contact friction during additional compaction. Compaction of the titanium hydride powder mixed with a water-soluble organic lubricant has been experimentally studied.
Keywords: long-length compacts; pressing; titanium hydride; porosity; additional compaction; lubricant

A multilayer Al5052–Cu composite is prepared by accumulative roll bonding (ARB) and the microstructure and mechanical properties are evaluated using optical microscopy, scanning electron microscopy (SEM), tensile tests, and micro-hardness measurements. The results show that the thickness (1000 μm) of copper layers of the initial sample is reduced to ~7 μm after the fifth ARB cycle, while the thickness of Al layer increases. With increasing number of ARB cycles, the microhardness of both aluminum and copper layers is significantly increased. The tensile strength of the sandwich is enhanced continiousely, and the maximum value of 566.5 MPa is achieved. The high strength of 566.5 MPa and ductility of 9.61% is achieved, which is ~47 and ~21% higher, than the maximum values found out in the publications. The investigation of the tensile fracture of surfaces during ARB indicates that the increase in ARB cycles changes the fracture mechanism to shear ductile.
Keywords: multilayer composite; Al–Cu; ARB; fractography; mechanical properties; microstructure

Effect of Spark Plasma Sintering on the Structure and Compressive Strength of Porous Nickel by Wei Feng; Qingyuan Wang; Qingquan Kong; Chenghua Sun; Xiaodong Zhu (154-160).
The effect of the temperature and time of spark plasma sintering (SPS) of a nickel powder on the structure of obtained samples of porous nickel was studied, and their mechanical strength under compression was evaluated. Based on the results of the experiments, it was found that spark plasma sintering the nickel powder at a temperature of 480°C with a holding time of 4 minutes enables to obtain samples with a porosity of 78.8%, having a structural performance and a compressive strength exceeding 1 MPa.
Keywords: spark plasma sintering; porous nickel material; structure; compressive strength

The state of the grain boundaries and the solid solution is analyzed for influence on the yield stress over a wide range of grain sizes for pure metals, low-doped alloys, and multicomponent solid solutions, including high-entropy alloys. A generalized equation is derived using the averaging integrals to describe the yield stress and hardness normalized to Young’s modulus versus the grain size. The potential to reach the maximum hardening for nanostructured materials through the use of grain-boundary engineering is considered. The concept of ‘useful’ impurities intended to bring the strength of such materials to the level comparable with the maximum (theoretically) possible one (E/2π–E/30) is proposed.
Keywords: yield stress; grain size; grain boundaries; solid solution; metals; low-doped alloys

Structure and Mechanical and Tribotechnical Properties of Iron–High-Carbon Ferrochrome Doped with Ni3B Additions by V. A. Maslyuk; E. S. Karaimchuk; M. I. Podoprygora; V. T. Varchenko; I. A. Sytnyk (175-181).
The production conditions and mechanical and tribotechnical properties of iron–high-carbon ferrochrome FKh800 materials doped with nickel boride have been studied. It is shown that Ni3B additions promote the formation of a multiphase microheterogeneous matrix-reinforced structure consisting of chromium steel and solid inclusions of complex chromium–iron carbides such as Me7C3 and Me23C6. When the doping content increases from 3.5 to 7.0 wt.%, complex Fe–Cr carbides and carboborides form, decreasing the hardness and bending strength and increasing the abrasive wear resistance of the base material from 5.0 to 12.2 km/mm. The Fe–35% FKh800 materials containing 5–7 wt.% Ni3B are found to be promising as they combine acceptable mechanical properties and improved abrasive wear resistance.
Keywords: powder materials; composite; wear resistance; iron; nickel boride; sintering; hardness

Interaction of Structural Components of Titanium Composite in Vacuum at 1150°C by A. G. Kostornov; O. I. Fushchych; T. M. Chevychelova (182-185).
The interaction of a Ti + 10 Mo titanium alloy, which serves as a matrix in a tribological material, with calcium fluoride CaF2 and boron nitride BN, which play the role of a solid lubricant, during their heating and sintering in a vacuum of 10–3 Pa at 1150°C for 15 and 120 min, respectively, has been studied. In the heating of a Ti + 10 Mo + CaF2 model sample for 15 min and sintering of Ti + 10 Mo + CaF2 CAM1 for 120 min, calcium fluoride does not interact with the Ti + 10 Mo matrix and does not change its composition and structure; a transition layer between the matrix and solid lubricant does not form. Thus, calcium fluoride preserves its initial lubricating properties. In the sintering of Ti + 10 Mo + 13 CaF2 CAM1 for 120 min, a composite antifriction material with a microheterogeneous structure is synthesized. Its structure is a mixture of solid solutions of molybdenum in α- and β-titanium, which has a body-centered cubic lattice and face-centered hexagonal lattice, in which calcium fluoride CaF2 is distributed in the form of inclusions. In the heating of a Ti + 10 Mo + BN model sample for 15 min and sintering of Ti + 10 Mo + BN CAM2 for 120 min, the interaction of the Ti+10Mo alloy with boron nitride BN occurs to form a transition layer with the phase composition α-TiMo + TiB + TiN + BN. In the sintering of Ti + 10 Mo + BN CAM2 for 120 min, a composite material with a microheterogeneous structure is synthesized. Its structure is a solid solution of Mo in α-Ti with a face-centered hexagonal lattice, strengthened by products of interaction of titanium with nitrogen and boron, TiN and TiB, in which boron nitride BN is distributed in the form of inclusions.
Keywords: composite material; chemical and phase compositions; structure; bearing structural component; solid lubricant; temperature; synthesis; interaction

Wear-Resistant High-Temperature Composite Slide Bearings Based on Titanium Aluminides by K. O. Gogaev; V. A. Barabash; A. N. Demidik; A. I. Bykov; V. T. Varchenko; V. L. Syrovatka (186-189).
The structure and properties of composite materials have been studied versus their composition. Comparative analysis of intermetallic titanium materials in dry friction with steel has been carried out. The intermetallic titanium material whose structure is represented by an intermetallic matrix with solid-phase inclusions has the highest tribotechnical properties.
Keywords: intermetallic titanium material; doping element; deformation; friction coefficient; wear

The microstructural and mechanical properties of a low alloy steel due to variations of temperatures were studied theoretically in this paper. In particular, the effects of microstructure, phase fractions, and local composition and area of single phases on the micromechanical behavior were considered. Based on these effects, a micro–macroscopic model was adopted to describe the hardening and fracture behaviors of this steel under some heat treatments. It was demonstrated that the flow curves under different intercritical temperatures could be well predicted by such model. Further simulation results showed that the high stress concentrated on the martensites, and the appearance of shear bands strongly depended on phase microstructures. In addition, it was found that the simulations on true stress–true strain curves at a macroscale were adequate for the prediction of damage behavior in different steels.
Keywords: heat treatment; steel; DP steel; macroscopic model

Effect of Molybdenum Additions on the Structure of TiB2–(Fe–Mo) Composite Materials by M. S. Storozhenko; O. P. Umanskyi; O. U. Stelmach; Ye. P. Pukhachevska; O. D. Kostenko; O. A. Bondarenko (200-208).
To examine the effect of molybdenum additions on the structurization of TiB2–(Fe–Mo) composite materials, differential thermal analysis of the samples with 8, 13, and 20 wt.% Mo in the metallic phase was carried out and their structure was examined after sintering. It is shown that molybdenum is an active component in the systems with 8 and 13 wt.% Mo and promotes the formation of complex Mo2FeB2 borides, which additionally strengthen the material. When the molybdenum content of the metallic phase increases to 20 wt.%, boride compounds intensively form in the system, making the composite material brittle.
Keywords: composite materials; structure; iron; molybdenum; titanium diboride

Production and Properties of B4C–TiB2 Composites with Isotropic Eutectic Microstructure by I. O. Husarova; O. M. Potapov; Ie. V. Solodkyi; Iu. I. Bogomol (209-214).
Directionally reinforced B4C–TiB2 eutectic alloys were produced from green powder compacts by floating zone melting. Their mechanical properties were studied over a wide range of temperatures (25–1600°C). The high-temperature strength of the reinforced B4C–TiB2 composites hardly changes with increasing temperature and reaches about 200 MPa at 1600°C. Mechanical grinding and subsequent spark plasma sintering were used to produce reinforced B4C–TiB2 composites with an isotropic eutectic microstructure. The microstructure of the bulk-reinforced ceramic samples was examined. The developed ceramics meet the requirements imposed on high-temperature creepresistant and oxidation-resistant materials for reusable hypersonic vehicles.
Keywords: eutectic alloys; composite; microstructure; ceramics; reusable hypersonic vehicles

Use of Binary Titanium–Chromium Diboride for Producing Protective Coatings on a Nickel Substrate by V. K. Mediukh; V. F. Labunets; R. M. Mediukh; G. N. Makarenko; E. V. Korbut; V. V. Zahrebelnyi; L. A. Krushinskaya; I. V. Uvarova (215-220).
The production of composite electrolytic coatings on a nickel substrate using binary titanium–chromium diboride obtained by mechanical synthesis was studied. The influence of heat treatment parameters on the phase composition and structure of the coatings was examined. It is shown that these coatings substantially increase the wear resistance of structural medium-carbon steel.
Keywords: composite electrolytic coatings; binary titanium–chromium diboride; heat treatment; structurization; wear resistance

Features of High-Temperature Oxidation of High-Entropy AlCrFe3CoNiCu Alloy by M. V. Karpets; V. F. Gorban; O. A. Rokitska; M. O. Krapivka; E. S. Makarenko; A. V. Samelyuk (221-228).
The paper examines how the scale forms on the AlCrFe3CoNiCu alloy when oxidized at 900°C for 50 h and how high-temperature annealing influences the structure and phase transformations and mechanical properties of the alloy matrix. It is found that long-term annealing at 900°C leads to the formation of a three-phase alloy consisting of a solid solution with a BCC lattice of B2 structural type and two solid solutions with FCC crystal lattices (one contains a higher amount of Ni and Co, and the other is a solid solution enriched with 66 wt.% Cu). A two-phase scale containing Al2O3 and CuO forms on the alloy in the oxidation process. Indentation method has shown that the mechanical properties of the AlCrFe3CoNiCu alloy remain stable after long-term high-temperature annealing.
Keywords: high-entropy alloy; oxidation resistance; scale; oxide; solid solution; σ-phase; hardness; microstructure

Interaction of (Ti, Cr)B2-Based Composites with a Nickel Alloy by O. N. Grigoriev; V. P. Konoval; A. D. Panasyuk; V. F. Chorunov (229-234).
The paper examines how the Ni–Zr–Cr alloy wets (Ti, Cr)B2, AlN, (Ti, Cr)B2–AlN, and AlN–(TiB2–TiSi2) refractory materials. The wetting of (Ti, Cr)B2 leads to near-zero contact angles. The introduction of AlN additions deteriorates wetting of the refractory materials by the nickel alloy, and the Ni–Zr–Cr alloy does not wet pure aluminum nitride. There is insignificant diffusion of Zr to (Ti, Cr)B2 in contact of the alloy with the refractory materials. There is no interaction in the AlN–(Ni–Zr–Cr) system. The composite materials are promising for use in contact with high-temperature corrosive alloys.
Keywords: nickel alloys; wetting; contact interaction; titanium–chromium diboride; aluminum nitride

The Particle Size Effect of Air-Exposed Zr–Mn–Cr–Ni–V Alloy on the Cyclic Resistance of Electrodes for Metal Hydride Batteries by Yu. M. Solonin; O. Z. Galiy; K. A. Grayvoronska; A. V. Sameljuk; I. A. Polishko (235-241).
The influence of the particle size and porosity of electrodes on their cyclic resistance was studied. It is found that the particle size influences the cyclic resistance of electrodes compacted from the air-exposed Zr–Mn–Cr–Ni–V alloy powder, while this effect is negligible for electrodes made of the unexposed powder. The maximum resistance is shown by electrodes with the smallest particle size. Treatment of the electrodes in a 30% KOH solution improves their activation and hardly affects their cyclic resistance. Decrease of the binder content from 5 to 3% increases the maximum discharge capacity of the electrodes and slightly improves the cyclic resistance. Increase in the binder content from 5 to 10% reduces the porosity of the electrodes, which leads to their faster failure. According to X-ray diffraction, the phase composition and crystallite size of the alloy powders with particles smaller than 100 μm and with 70–50 μm and 50–40 μm particles after exposure in air for 10 days at room temperature remained unchanged.
Keywords: zirconium alloy; hydrogenation; exposure in air

Assessment of the Protective Properties of Impact-Resistant Ceramic-Polymer Composites Using Acoustic Nondestructive Methods by Yu. G. Bezimyanniy; L. R. Vyshniakov; O. V. Mazna; A. M. Vysotskyy; K. A. Komarov; O. V. Neshpor (242-249).
The use of acoustic nondestructive methods was studied with the purpose of determining the composition and structure of protective ceramic-polymer composites according to the criteria of penetration resistance and protective barrier endurance. The methods of acoustic measurements were adapted to the characteristics possessed by groups of samples from the following materials: ceramics, polymer composites, honeycomb-structure materials, and ceramic-polymer composites. Stiffness, ρc2, was used as an informative parameter to define the elasticity of the materials in the direction of impact, and frequency drift was used as a measure of elastic wave dissipation. The measured acoustic characteristics of the samples were compared to the known criteria for penetration resistance of ceramics and the results of ballistic tests. The ceramic-polymer material with a gradient support demonstrated better ballistic endurance and lower after-penetration deformation. The material is recommended for the production of efficient impact-resistant composites possessing enhanced dissipative capabilities.
Keywords: acoustic nondestructive methods; ceramic-polymer protective materials; penetration resistance criteria; protective barrier endurance; stiffness