Powder Metallurgy and Metal Ceramics (v.48, #3-4)

Effect of biological media on the physical, chemical, and magnetic properties of carbonyl iron and nickel powders by O. A. Ivashchenko; N. V. Boshitska; A. O. Perekos; V. Z. Voinash; V. P. Zalutskii; I. V. Uvarova (125-132).
The paper examines changes in carbonyl iron and nickel powders subjected to model biological media: water media and media containing human blood plasma. It is established that carbonyl iron powder interacts with biomedia containing blood plasma six times as fast as with water media. No oxidation or corrosion is observed in the process. The magnetic properties of the powder after the interaction with plasma-containing media do not practically deteriorate. Iron powder is intensively absorbed by blood plasma, Fe3+ ions forming complex compounds with proteins. On the contrary, carbonyl nickel is not absorbed by blood plasma for five days, and the powder specific surface area and particle morphology remain practically unchanged after the interaction. Blood plasma seems to dissolve and transform metals according to the human body’s demands. In the case of carbonyl iron, this process proceeds faster than corrosion does. In the case of carbonyl nickel, the opposite is observed.
Keywords: carbonyl iron; carbonyl nickel; biological media; human blood plasma; powder specific surface area; magnetic properties

Strain hardening of a powder body in pressing by M. S. Koval’chenko (133-144).
The compaction of powders in a press mold is analyzed using the theory of plasticity for porous and powder bodies and a rheological model that includes elastic, viscous, and plastically hardenable elements of the matrix forming a porous deformable body. In cold-pressing conditions, plasticity is the main factor influencing the behavior of the porous body under external pressure. The shear yield stress of the matrix versus its mean-square-root strain is calculated. It is shown that the dependence of the mean relative density of a compactable body on the applied pressure is determined by the variation in the shear yield stress of the matrix due to strain hardening for metal bodies and due to the brittle fracture of particles along with strain hardening during compaction for non-metal powders. An analysis of data on powder compaction under continuous pressure increase by calculating the above dependences shows features of matrix strain hardening and their effect on powder compaction in a press mold.
Keywords: powder body; compaction; yield stress; strain; hardening

A new numerical approach is proposed to model powder pressing. It is called direct multiscale modeling. In direct multiscale modeling, each macroscopic finite element has a corresponding microstructure regarded as a powder representative cell. On the assumption that the strain rate of the macroscopic finite element and average strain rates of the representative cells are equal, the kinetics of macroscopic deformation and microscopic distortions of the representative cells is determined at every instant. The problem dealing with the effect of the initial spheroidization of intraagglomerate pores on the compaction of agglomerated powders is considered as an example. The new approach permits assessing the effect of the initial intraagglomerate pore shape on the closure kinetics of interagglomerate pores in pressing.
Keywords: modeling; powder pressing; multiscale approach

Asymmetric rolling of metal powders. I. Compactability of metal powders in asymmetric rolling by K. A. Gogaev; G. Ya. Kalutskii; V. S. Voropaev (152-156).
The compactability of iron powders and electrolytic titanium using driven rolls of different diameters at the same angular velocity is examined. The roll diameter ratio is 1.12 to 1.42. It is established that the rolling force can be decreased from 20 to 50% in asymmetric rolling depending on variation in the mismatch of circumferential velocities or diameters of the rolls as compared with conventional (symmetric) rolling at the same density of rolled product.
Keywords: density; rolling; powder; asymmetry; maximum normal contact stress

Epoxy composite materials (ECMs) and composite protective coatings are important for the improvement and further development of many engineering areas. Owing to the combination of components with different physical, chemical, thermal, and mechanical properties, ECMs have unique adhesive strength, wear resistance, heat resistance, and corrosion resistance. To obtain ECMs, ÉD-20 epoxy resin, polyethylene polyamine as a curing agent, modifiers, and multifunctional reinforcements are used. Methods to control the structure and properties of ECMs with different reinforcement contents are justified and structurization mechanisms depending on the nature and morphological features of the ingredients and their ratio in the system are established in comprehensive research. The rheological properties of epoxy composites depending on the reinforcement content are analyzed. The classification of epoxy composites into low-reinforced, medium-reinforced, and high-reinforced systems is shown to be reasonable. Predominant factors that influence the properties of relevant materials are identified.
Keywords: rheological properties; reinforcement content; composite; epoxy binder; system

Sintering of hybrid skeletal materials containing voids filled with powder by M. B. Shtern; A. V. Kuz’mov; V. V. Skorokhod (162-168).
The sintering behavior of a skeletal material whose cells contain powder is analyzed. The analysis is based on the simulation of this process using the continuum theory of sintering. The calculations are performed with the finite-element method. Special attention is paid to the distortion of cells and evolution of porosity distribution within the cells during sintering. If the powder and skeleton are bonded, combinations of cell and wall sizes and initial porosity are such that internal cavities can form between the powder and skeleton walls after sintering.
Keywords: sintering; skeletal material with powder reinforcement; continuum theory of sintering; shrinkage inhomogeneity in sintering

A plastic particle will adhere to a substrate after collision if the work of adhesion in the contact area exceeds the elastic rebound energy. The plastic deformation of the particle decreases the elastic strain energy and increases the probability of adhesion. A linear hardening plastic material with constant hardening modulus is used as a model. The particle is modeled by a disk with onedimensional stress distribution. Equations are derived to calculate the minimum speed of impact for the particle to stick to the substrate and the degree of “flattening” of the particle after collision. The model includes no empirical coefficients to be determined in spaying experiments. A new method to describe the effect of dynamic interaction on the activation energy for a topochemical reaction is proposed. It is demonstrated that the nature of plastic deformation changes after the contact stress becomes equal to the hardening modulus. In a high-speed impact, almost all of the kinetic energy is transformed into heat even if the plastic particle does not adhere to the substrate. The calculated results are in agreement with experiments on an aluminum powder deposited by cold spraying onto a copper substrate.
Keywords: powder spraying; high-speed collision; plastic deformation; hardening modulus; topochemical reaction

Influence of ZnO specific surface area on its sintering kinetics by N. Obradovic; S. Stevanovic; V. Zeljkovic; M. M. Ristic (182-185).
The aim of this work is an investigation of isothermal sintering kinetics by observing the reduction of the specific surface area of ZnO. Zinc oxide powder is sintered isothermally in air for 5 to 120 min at temperatures from 400 to 900°C. The decrease in the specific surface area is observed as a function of temperature and sintering time. Models of Ristic–Jovanovic and German are applied in order to define the appropriate parameters. Information on the activation energy of sintering is obtained by the Arrhenius equation. The least square estimation (LSE) method was applied for determining optimum parameter values.
Keywords: sintering; kinetics; specific surface area; zinc oxide powder

Effects of processing parameters on the temperature field of selective laser melting metal powder by Ruidi Li; Yusheng Shi; Jinhui Liu; Huashan Yao; Wenxian Zhang (186-195).
Based on temperature-dependent thermophysical parameters and nonlinear phase transformation from powder to liquid, a three-dimensional transient thermal finite model of selective laser melting process is developed. Commercial ANSYS software is used to simulate the distribution of the temperature field in selective laser melting. The simulation results show that a lower scan speed, higher laser power, and a lower scan interval enable much higher maximum temperature in the powder bed and wider scan track width. The scan modes also have great influence on the temperature field. Temperature in the powder bed experiences fluctuant variation with transverse scan mode in contrast with moderate variation with lengthwise scan mode. The simulated results are compared with the experimental results and good agreement is found in scan track width.
Keywords: selective laser melting; 316L stainless steel powder; temperature field; numerical simulation; processing parameters

Effect of metal-layer structure on the mechanical properties of multilayer metal–ceramic composites. II. Heat resistance by P. Ya. Radchenko; V. V. Panichkina; O. I. Get’man; M. G. Andreeva; V. V. Pasichnyi; S. A. Ostapenko (196-200).
The effect of the metal-layer structure and of the interface between the ceramic and metal components on the heat resistance of multilayer ceramic–metal composites is examined. The use of metal fabric layers substantially enhances the heat resistance of composites. The adverse effect of the residual porosity and, sometimes, poor adhesion between the ceramic and metal phases on heat resistance decreases owing to the skeleton structure of metal layers. The skeleton structure of metal layers promotes crack branching and retards the formation of the main crack.
Keywords: multilayer ceramic–metal composites; microstructure; heat resistance

The mechanical properties of porous titanium samples in vacuum sintering are analyzed. The effect of porosity and initial powder size on conductivity, static and dynamic elastic moduli, ultimate strength, and strain to failure is examined for sintering temperatures between 300 and 1200°C. The quality of contact in materials in different structural states is subjected to a comparative analysis.
Keywords: porosity; mechanical properties; powder titanium; resistivity; elastic modulus

Effect of deformation processing on the properties of Cu–50% Cr composite by E. V. Khomenko; G. A. Baglyuk; R. V. Minakova (211-215).
The paper examines the structure, density, resistivity, and mechanical properties of Cu–50 wt.% Cr powder composite after liquid-phase sintering at 1200°C in hydrogen and subsequent deformation processing: additional cold pressing under 550–600 MPa, sintering under 8.5 MPa at 1100°C, and hot forging beginning from 850°C. It is shown that the maximum compaction of the composite (up to 99% of the theoretical density), decrease in its resistivity, and increase in strength and plasticity are reached in hot forging in a closed die mold and subsequent annealing at 600°C to relieve internal stresses.
Keywords: composites; sintering under pressure; hot forging; structure; mechanical properties

The behavior of orthopedic implants in the human body, interaction of implant materials with biological fluids and tissues, and response to external stresses are examined. The modified biofunctionality criterion is suggested to incorporate porosity. The following criteria are proposed for the objective selection and correct assessment of implant materials: medical and biologic (biocompatibility), biomechanical (modified biofunctionality index BF), biopower (cosine of the wetting angle for biological fluid), biochemical (degree and kinetics of adhesion of cell cultures from solutions to implant materials), electrophysical (potential, electron work function and other surface characteristics), topographical (conformity of macro- and microrelief of the surface to tissues), and adaptive (transformability, adaptation to the body’s influence and stresses, ability to self-organization).
Keywords: implant; bioinactivity; biotolerance; bioactivity; biocompatibility; functionality assessment criteria

Al2O3–HfO2–Y2O3 phase diagram. I. Isothermal sections at 1250 and 1650°C by S. M. Lakiza; Ya. S. Tishchenko; V. P. Red’ko; L. M. Lopato (225-233).
Isothermal sections at 1250 and 1650°C in the Al2O3–HfO2–Y2O3 phase diagram are plotted for the first time. Phase equilibria are established at these temperatures. No ternary compounds and appreciable solid solution regions based on binary compounds are found in the ternary system.
Keywords: ceramics; hafnia; alumina; yttria; interaction; isothermal section; phase diagram; eutectic materials

Aurum and europium mixing enthalpies by M. I. Ivanov; V. V. Berezutskii; N. I. Usenko (234-237).
The mixing enthalpies of liquid Au–Eu alloys are measured by isoperibolic calorimetry at 1480 K within the entire concentration range for liquid components. Extremely large exothermal mixing effects are found (ΔH min = −47.3 ± 1.6 kJ/mole), which is evidence of very intensive interaction between the components.
Keywords: aurum; europium; melts; enthalpy; calorimetry

Hydrothermal decomposition, hydrothermal crystallization, hydrothermal homogeneous precipitation, microwave hydrothermal synthesis, ultrasonic-assisted hydrothermal synthesis, hydrothermal synthesis under supercritical conditions, which are used to produce ZrO2-based nanocrystalline powders, are considered. It is established that the nucleation and particle growth can be controlled in hydrothermal synthesis (through concentration change, increase or decrease in hydrolysis temperature, increase in hydrolysis time, introduction of surface active agents during dehydration, pH change during removal of admixtures, etc.) and thus high-pure homogenous powders with particles of different shapes can be produced in these conditions. They do not require additional grinding or thermal treatment at high temperatures, which usually involves the pollution of powders and decreases their activity in sintering. It is shown that the powders are used to produce transformation-hardened ceramics, catalyst supports, thick films, oxygen sensors, materials for solid oxide fuel cells (SOFC), electrochemical oxygen pumps, thermal-barrier coatings, and bioinert implants.
Keywords: hydrothermal decomposition; hydrothermal crystallization; hydrothermal homogeneous precipitation; microwave radiation; ultrasonic hydrothermal synthesis; synthesis under supercritical conditions; zirconia