Powder Metallurgy and Metal Ceramics (v.46, #11-12)

The mechanical properties of hard WC-Co alloys produced by solid-phase sintering at various temperatures are discussed. It is shown that the bending strength and hardness of these alloys may be the same as those achieved in liquid-phase sintering. The difference between solid-phase and liquid-phase sintering is only in the time it takes to achieve the dense state. Excellent mechanical properties at rather low temperatures (1150–1200 °C) can be obtained by sintering under pressure. High hardness can be achieved at 1000–1100 °C by hot isostatic pressing of nanoscale powders. The excellent mechanical properties of solid-phase-sintered hard WC-Co alloys indicate that strong interphase and intercarbide boundaries occur earlier than the liquid phase.
Keywords: hard metal; solid-phase sintering; mechanical properties

Reactive electric-discharge sintering of TiN-TiB2 by A. S. Petukhov; I. V. Khobta; A. V. Ragulya; A. V. Derevyanko; A. I. Raichenko; L. P. Isaeva; A. M. Koval’chenko (525-532).
Powder mixtures based on titanium and its dihydrides are sintered by electric discharge in a certain current mode to produce TiN + TiB2 composites. It is established that the use of tetragonal titanium hydride as the starting material results in the complete synthesis leading to a TiN + TiB2 composite. The higher shrinkage rate results from the higher purity of titanium dihydride, which, in its turn, increases the partial pressure of hydrogen in the reaction area and the reaction rate. Tetragonal titanium hydride is more preferable than cubic hydride and metal titanium. The microstructure of alloys resulting from the sintering of hydride-based mixtures is more homogenous: it includes equiaxial grains with the mean size of about 1 µm.
Keywords: titanium hydride; titanium nitride; titanium diboride; ceramic composite material; reactive electric-discharge sintering

The effect of Fe addition on the densification of B4C powder by spark plasma sintering by N. Frage; S. Hayun; S. Kalabukhov; M. P. Dariel (533-538).
Boron carbide is a low-density ceramic with high hardness and stiffness values that make it a valuable candidate for light armor applications. Fully dense boron carbide is fabricated by hot pressing of fine (<2 µm) powder at a relatively high temperature (2150–2200°C). Fully dense boron carbide can be processed from an initial mixture of 5.5 vol.% Fe and low-cost B4C powder by spark plasma sintering (SPS) at 2000°C. At this temperature, Fe-free boron carbide can be consolidated only to 96% of the theoretical density. The effect of the Fe addition on the densities is even more pronounced at lower processing temperatures and is related to the presence of a liquid phase in the Fe-containing material. The resulting microstructure and mechanical properties of the Fe-containing boron carbide are presented and discussed.
Keywords: powder; boron carbide; iron; sintering; spark plasma; mechanical properties; structure

Effect of electrospark alloying on the wear resistance of cutting inserts made of VK8 alloy by O. V. Stepanova; I. A. Podchernyaeva; A. D. Panasyuk; I. V. Uvarova; I. I. Timofeeva; A. A. Rogozinskaya (539-542).
The paper presents the results from x-ray phase analysis and wear-resistance tests (discontinuous cutting) of cutting inserts made of VK8 (WC-8% Co) hard alloy. The inserts have an electrosparkdeposited coating based on the AlN-Ti/ZrB2 system with Ti/ZrSi2 additions and the TiN-AlN system. These results allow one to infer the possible causes of different wear resistance of cutting inserts with electrospark-deposited coatings. Among such causes are intensive oxidation of titanium (unlike zirconium) during electrospark alloying followed by the formation of brittle oxide phases and the shielding effect of ZrO2 (it prevents globules from destruction during both alloying and service).
Keywords: hard alloy; electrospark alloying; x-ray phase analysis; wear resistance; cutting face

Hard plasma chemical coatings based on silicon carbon nitride by L. A. Ivashchenko; V. I. Ivashchenko; O. K. Porada; S. M. Dub; P. L. Skrinskii; M. V. Ushakov; M. V. Karpets; A. I. Stegnii; L. A. Grishnova (543-549).
Silicon carbon nitride (SiCN) coatings deposited on a silicon substrate are produced by plasma-enhanced chemical vapor deposition (PECVD) using methyltrichlorosilane (MTCS), nitrogen, and hydrogen as starting materials. The coatings are characterized with AFM, XRD, and FTIR. Their mechanical properties are determined with nanoindentation. The abrasion wear resistance is examined using a ball-on-plane (calowear) test and adhesion to the base using a scratch test. The x-ray diffraction indicates that the coatings produced at moderate FN are nanostructured and represent β-C3N4 crystallites embedded into the amorphous a-SiCN matrix. The coatings deposited at a higher nitrogen flow rate are amorphous. The nanostructure is supposed to result from an increase in hardness (25 GPa) and Young’s modulus (above 200 GPa). The tribological tests have revealed that the friction coefficients of the coatings containing nitrogen are two to three times smaller than those based on SiC and deposited on a silicon substrate. The ball-on-plane tests show that the nanostructured coatings also exhibit the highest abrasive wear resistance. These findings demonstrate that the SiCN films deposited using MTCS show good mechanical and tribological properties and can be used as wear-resistant coatings.
Keywords: nanocrystalline coating; silicon carbon nitride; plasma-enhanced chemical vapor deposition (PECVD); methyltrichlorosilane (MTCS); nanoindentation; adhesion; friction; microabrasive wear

Alloys and phase equilibria in the Al-Ti-Rh system. II. Melting diagram of the TiRh-Rh-AlRh partial system by K. E. Kornienko; V. G. Khoruzha; P. S. Martsenyuk; A. V. Samlyuk (550-555).
Data on the solidus surface of the partial TiRh-Rh-AlRh system and results of metallography, x-ray diffraction, and differential thermal and electron microprobe analyses of its as-cast alloys are used to project the liquidus surface of this system onto the concentration triangle and examine the processes occurring in the crystallization of its alloys for the first time. This makes it possible to plot the melting diagram of the partial TiRh-Rh-AlRh system. Its liquidus surface is completed with four surfaces of primary crystallization of solid solutions based on rhodium and phases based on binary compounds formed in the bounding binary Al-Rh and Ti-Rh systems. In the partial TiRh-Rh-AlRh system, there are two invariant four-phase equilibria involving liquid; one of them is peritectic (at 1714°C) and the other is eutectic (at 1675°C). These four-phase equilibria also include five monovariant three-phase equilibria involving a liquid phase.
Keywords: liquidus surface; crystallization; phase; melting diagram

Ti-TiNi-HfNi-Hf Liquidus surface by O. L. Semenova; L. O. Tret’yachenko; V. M. Petyukh (556-564).
Physical and chemical analysis methods are used for the first time to examine the Ti-TiNi-HfNi-Hf alloys in the melting-crystallization region. The liquidus surface is shown to consist of six fields of primary phase crystallization: λ1, η, δ, θ, β, and α. The largest fields are of δ-and β-phases. The λ1 ternary phase is formed by peritectic reaction l + δ → λ1. There are five invariant equilibria involving liquid on the Ti-TiNi-HfNi-Hf solidus surface. The liquidus surface, vertical sections, and alloy crystallization scheme are constructed.
Keywords: liquidus; invariant equilibrium; metatectic reaction; peritectic reaction; comparative differential thermal analysis

The CALPHAD method is used for thermodynamic description of binary copper systems with transition metals based on data on the thermodynamic properties of phases and phase transformations. The parameters of models describing the temperature-concentration dependence of thermodynamic functions of mixing are obtained, and the phase diagrams of the systems are calculated. An analysis of the models makes it possible to establish the behavior of the temperature-concentration dependence of the excess thermodynamic functions of mixing for liquid alloys with different types of interaction of the components and to calculate the excess heat capacity. A correlation between the excess heat capacity of liquid alloys and the mixing enthalpy is established.
Keywords: thermodynamics; thermodynamic modeling; excess thermodynamic functions of mixing; temperature-concentration dependence; excess heat capacity of liquid alloys; copper-based alloys

Oxidation of TiAl intermetallic by V. G. Chuprina; I. M. Shalya (582-588).
The oxidation kinetics of TiAl intermetallic at 500–900 °C in air is studied using a gravimetric method, and the phase composition of the scale is studied using an x-ray phase analysis. At t > 600 °C, the kinetics of oxidation is described by a parabolic equation. The oxides TiO2 (rutile), γ-Al2O3, α-Al2O3, Ti2O3 are found in the scale. It is shown that at the first stage the γ-Al2O3 and low-titanium oxides form on the sample surface at t < 70 °C. At t ≥ 850 °C, the Ti2O3 forms on the external surface of the scale, TiAl3 is found in the sublayer at the alloy/scale interface. It is shown that at t ≤ 800 °C the process is controlled by oxygen diffusion. At t > 800 °C, the oxidation mechanism changes: counterdiffusion of titanium ions through interstitial sites in TiO2 lattice occurs.
Keywords: intermetallic compounds; oxidation; kinetics; phase analysis; diffusion

Structurization in sintering of antifriction powder materials based on iron-copper alloys by A. G. Kostornov; O. I. Fushchich; T. M. Chevichelova (589-594).
The paper studies the contact interaction of the components in powders Fe-(Cu + Sn), Fe-(Cu + Sn + P + Pb), and Fe + B-(Cu + Sn + P + Pb) during sintering in hydrogen at 920 °C. It is shown that this interaction is responsible for the formation of both the interphase boundary and the general structure that defines the performance characteristics of an antifriction material. The interface and the phase and chemical composition of the products of interaction are examined. It is established that the powder composition Fe + Cu + Sn + P + B + Pb sintered in hydrogen at 920 °C is a microheterogeneous material whose matrix, which takes up the major load during friction, includes two phases: one based on iron alloyed with boron (Fe2B), copper, tin, and phosphorus and the other based on copper including tin in the form of α-solid solution, phosphorus in the form of Cu3P, and iron. Lead uniformly distributed over the matrix volume is the antifriction component of the material.
Keywords: powder composition; microheterogeneous structure; matrix; antifriction component; sintering; interaction; interface; phase; volume diffusion; boundary diffusion

This paper reviews works on the use of transition-metal carbides and presents results of the author’s own research on the abrasive machining of mechanical engineering materials. It is established that the properties of abrasive grains are primarily controlled by the abrasive nature and production process. It is shown that carbides of transition metals are efficient for use in abrasive tools (grinding disks, pastes for processing mechanical engineering parts from various materials).
Keywords: material; abrasive; carbide; machining; abrasive tool

Developmental trends in European Powder Metallurgy by V. M. Kryachek; D. A. Levina; L. I. Chernyshev (608-612).
The state of the art and development trends in European powder metallurgy are analyzed. The main ways to improve the production technology and quality of parts are discussed. It is pointed out that the injection-molding production of powder-metallurgy parts is rising. The areas of their application are analyzed. It is informed that European research centers and development programs on powder metallurgy grow in number. The role of the European Powder Metallurgy Association is indicated.
Keywords: powder metallurgy; powder; parts; technology; injection molding; slip; production; press; furnace; data bank