Powder Metallurgy and Metal Ceramics (v.50, #9-10)

Corrosion resistance of phosphorus-clad iron powders in biological and inorganic media by N. V. Boshitska; O. V. Vlasova; L. M. Apininska; L. S. Protsenko; O. M. Budilina; I. V. Uvarova (573-578).
The production and use of clad iron-based powder materials is a promising area of powder metallurgy that allows variation in their process and magnetic properties in wide ranges. The corrosion properties of phosphorus-clad iron powders and their interaction with biological media of the living organisms are studied. The PZhRV 3.200.26 (Ukraine), AHC 100.29 (Sweden), and PZhV 200 (Russia) iron powders with different particle sizes are clad with phosphorous by the method of thermochemical decomposition of phosphorous compounds and by the method of thermochemical synthesis in a vibrating bed. Corrosion tests of the iron powders clad with phosphorous are performed in a 3% NaCl solution. Calculations of the corrosion depth index show that the clad powders are much more resistant to corrosion in aggressive media (3–4 points according to the ISO 11130:2010 standard) than the starting powders (1 point). The low values of the corrosion depth index of phosphorus-clad powders testify that surface corrosion proceeds on powder particles. It is shown that the interaction of the starting PZhRV 3.342.28 and AHC 100.29 iron powders with human blood plasma is 5.8 and 7.2 times more intensive, respectively, than that for PZhRV 3.342.28 and AHC 100.29 powders clad with phosphorous. On the surface of iron powders, phosphorus interacts with blood plasma proteins to form a protective colloidal biocomplex, which increases substantially the resistance of clad powders in blood plasma. Thus, the cladding of iron powders with phosphorus enhances significantly their chemical stability both in human blood plasma and in air.
Keywords: iron powders; biological media; corrosion

Warm compaction of the gearbox synchronizing ring of Belarus tractors: computer simulation by V. M. Gorokhov; O. V. Mikhailov; M. B. Shtern; A. F. Ilyushchenko (579-585).
Computer simulation has been used to study the warm compaction of complex powder parts. Relations of the plasticity theory for porous bodies and finite-element method are employed. The effect of the velocity ratio of different pressing elements on the density distribution is analyzed. The possible nonuniformity of density distribution is due to external friction and complex shape of parts. The optimal ratio is found. All other velocity ratios of pressing elements lead to unacceptable distribution of properties in powder parts.
Keywords: warm compaction; plasticity theory for porous bodies; computer simulation; finite-element method; pressing patterns; distribution of relative density

A comparative study is conducted by compaction experiments and finite element simulations on the compaction behavior of multiple alloy powders in the traditional single direction compaction and in the friction-assisted-compaction processes. The results suggest that, in the single direction compaction, stress, strain, and density of the green compacts along the vertical direction are not uniform due to the effects of the friction between the side die wall and powder particles; the density on the top of the green compacts is higher than that in the bottom. However, in the friction assisted compaction process, the density distribution along the vertical direction is more uniform and the density near the middle part of the green compacts is only slightly lower than that at the top and bottom parts of the green compact.
Keywords: multiple alloy; single direction compaction; friction assisted compaction; finite element simulation

The electrical aspects of spark-plasma sintering (SPS) of TiH2–BN and Ti + BN powder mixtures for the production of a TiN–TiB2 ceramic composite material are studied, and the dependence of its properties on direct-current density at the initial stage of sintering is established. To determine the direct-current density, a method for calculating the effective cross-sectional area S eff of the die–sample circuit is proposed. At the initial stage of sintering, the major portion of the current flows through the graphite die because of the resistance of the contacts and the presence of α-BN dielectric. At the final stage of sintering, the current flows mainly through the sintered sample because of the synthesis and densification of the TiN + TiB2 composite and, consequently, the abrupt increases in the conductivity of the sintered sample. Increasing the initial direct-current density during the sintering of TiH x hydride samples leads to an increase in relative density (conductivity), microhardness, fracture toughness, and abrasive wear resistance.
Keywords: electrical parameters; ceramic composite material; TiN + TiB2 ; spark-plasma sintering

The paper discusses the prospects of layer-by-layer synthesis of porous tissue scaffolds (matrices) of titanium and NiTi (nitinol) as a repository for stem cells. The experiments are performed on primary cultures of human dermal fibroblasts of 4–18 passages. The culture of dermal fibroblasts is obtained from the skin and muscle tissue of 6 to 10-week abortuses with the method of primary explants. The role of surface morphology of porous matrices of these materials in cell adhesion and proliferation is examined in comparison with cast dental titanium. The surface microstructure and roughness are analyzed with optical and scanning electron microscopy before and after experiments in vitro. The elemental analysis is used to determine the biochemical composition of post-experimental porous matrix structures. The results show high chemotaxis of cells to the samples and effect of the matrix composition on the development of cell culture.
Keywords: titanium; nitinol; tissue scaffold; selective laser sintering; osseointegration; multipotent mesenchymal stromal cells; differentiation; bone formation; porous matrix

A relatively simple process for coating of porous powder steel parts with a wear-resistant porousless layer of white cast iron has been developed. The wear resistance of the coating is comparable with that of high-chromium cast iron.
Keywords: powder steel; electrocontact thermochemical treatment; white cast iron; wear resistance

Composite WC–35% Ni produced from ultrafine WC + NiO powders. II. mechanical properties by A. I. Tolochin; A. V. Laptev; I. Yu. Okun; M. S. Kovalchenko (625-631).
The mechanical characteristics of ultrafine-grained WC–35 wt.% Ni composite produced by shortterm solid-phase pressing at different temperatures and at a pressure of ~1200 MPa are studied. The initial powder mixture consists of tungsten carbide and nickel oxide. One part of the mixture was reduced by hydrogen, while the other part was mixed with saccharose to reduce the oxide to nickel during heating of green briquettes. In the latter case, the synthesis of the metal phase and the consolidation of the WC–Ni mixture proceed in one stage. It is established that the powder mixture samples treated by hydrogen have lower bending strength if the composite is consolidated at temperatures below 1250°C. At this temperature, the samples acquire a bending strength of 2700–2800 MPa, irrespective of how the mixture was prepared. The liquid-phase consolidation of the composite leads to a decrease in the strength to 1800 MPa. It is shown that the fracture of the composite consolidated in the temperature range 950–1150°C occurs generally in the nickel matrix, which deforms severely before fracture in the composite pressed at 1150°C. The fracture toughness of the solid-phase compacted composite is ≥25 MPa ⋅ m1/2 and its hardness is higher than 6000 MPa.
Keywords: composite; hard alloy; mechanical properties; bending strength; tungsten carbide; hardness; fracture toughness; fracture

Production of laminated ceramic composites based on AlN and B4C and study of their properties by O. N. Grigorev; O. D. Shcherbina; V. N. Kirlas; A. K. Marchuk; I. L. Berezhinskii (632-640).
The properties of laminated ceramic systems, especially those with low-strength bonds, are discussed. It is shown that residual stresses, which depend on the physical and mechanical characteristics (such as strength, thermal expansion coefficient, thickness, intensity of interfacial interaction) and structure of the main layers and interlayers, affect the fracture behavior of composites. Laminated materials with low sensitivity to defects and strength as high as that of the main layer were produced using a number of oxygen-free refractory compounds.
Keywords: ceramics; laminated ceramic composites; hot pressing; stress

The data obtained by metallography, x-ray diffraction, electron microprobe and differential thermal analyses as well as by Pirani–Alterthum incipient melting technique are used to construct the solidus surface projection of the Ti–TiRh–AlRh–Al partial system onto the composition triangle for the first time. The participation of two ternary compounds (τ1, Al67Ti27Rh6, with AuCu3-type structure, and τ2, Al49.6Ti27.1Rh23.3, with Th6Mn23+1-type structure) in phase equilibria is confirmed. Thirteen single-phase surfaces corresponding to solid solutions based on components and to the phases based on binary and ternary compounds are found on the solidus surface. This surface also contains 25 ruled surfaces bounding two-phase volumes as well as 13 isothermal planes that are constituents of invariant four-phase equilibria.
Keywords: solidus surface; partial system; compound; isothermal plane

The paper studies the kinetics and mechanisms of anodic oxidation of aluminum alloys in the quasibinary section (α-Al–Mg2Si) of the Al–Mg–Si system in a 3% NaCl solution. According to the principle of independence of reactions, the electrochemical processes in two-phase alloys are shown to take place on each phase separately. On some areas of the surface, Al2O3 is formed as a reaction product, while α-SiO2 is formed on the other areas. It is established that the corrosion of the eutectic component occurs at the early oxidation stages, while α-Al dendrites are uniformly dissolved with a dominating transition of Mg2+ ions into the solution. The alloys that have the minimum amount of the eutectic component exhibit the highest corrosion resistance.
Keywords: aluminum alloys of Al–Mg–Si system; kinetics and mechanism of anodic oxidation; corrosion products; principle of independence of electrochemical reactions

Catalytic systems based on multicomponent oxides of 3d-metals and Si-containing carriers for CO oxidation reaction by O. V. Ishchenko; P. M. Silenko; T. M. Zakharova; A. V. Yatsimirskii; A. M. Shlapak; G. G. Tsapyuk (662-670).
The catalytic activity and surface properties of Cu–Co–Fe oxide catalysts formed on silica gel, powdery β-SiC, and β-SiC nanofibers for CO oxidation reaction are studied. A method, involving including initial acidic treatment of silicon carbide nanofibers with a mixture of hydrofluoric and nitric acids, has been developed for obtaining a highly defective surface layer for the formation of Cu2(OH)3NO3 active mass.
Keywords: CO oxidation; oxide catalysts; mass spectrometry; silicon carbide nanofibers; silica gel

Effect of magnetic field on residual stresses in NiAl–Re detonation coatings by E. N. Polyarus; V. E. Oliker; T. Ya. Gridasova; S. M. Chernega; E. F. Grechishkin (671-675).
The influence of a magnetic field on the internal stresses in NiAl–Re detonation coatings is experimentally confirmed. It is shown that the magnetic field has a substantial effect on the behavior and type of internal stresses. The changes are attributed to the residual stresses in the “substrate– coating” system, which are induced at all stages of preparation and subsequent treatment of the material in the magnetic field.
Keywords: magnetic field; internal stresses; detonation coating