Powder Metallurgy and Metal Ceramics (v.52, #11-12)

Sintering of Titanium, Silicon, and Titanium Silicide Powder Mixtures by G. A. Pribytkov; M. I. Vagner; V. V. Korzhova; E. N. Korosteleva; A. V. Gurskikh; I. A. Firsina (613-619).
Metallography, X-ray diffraction, and electron microprobe analysis are used to study Ti–Si materials containing up to 25 at.% Si produced by vacuum sintering of titanium, silicon, and titanium silicide Ti5Si3 powder mixtures. The results of structural studies are interpreted to explain volumetric changes during sintering of samples with different original phase compositions. It is established that the replacement of silicon by titanium silicide in the powder mixtures with titanium results in a multiple decrease in the porosity of sintered composites.
Keywords: titanium; silicon; silicides; powder alloys; vacuum sintering; structurization; volumetric change

‘Fluoroplastic–Multi-Walled Carbon Nanotube’ Composites: Structural, Mechanical, and Tribotechnical Characteristics by Yu. M. Solonin; A. V. Nenakhov; A. G. Kostornov; N. I. Danilenko; V. F. Gorban’; M. V. Karpets (620-631).
The paper studies the production of ‘fluoroplastic–carbon nanotube’ composites, analyzes their structure, and determines their mechanical and tribotechnical characteristics. The properties of the composites depending on the reinforcement content are examined. It is established that addition of only 3% carbon nanotubes significantly increases the hardness and Young’s modulus while the wear becomes two orders of magnitude lower under friction without lubrication. The structure of ‘fluoroplastic–carbon nanotube’ composites is analyzed in detail. A mechanism whereby carbon nanotubes influence the mechanical characteristics and wear resistance is proposed.
Keywords: fluoroplastic; carbon nanotubes; composite; hardness; Young’s modulus; wear resistance

Literature overview and our own results are used to identify the most promising areas of research in the field of titanium porous powder materials (PPMs). The search for possible ways of further reduction in PPM cost is a relevant area. It includes not only the use of sponge titanium powder and titanium sponge as the feedstock but also titanium hydride powder and, in the long term, enriched rutile concentrate. The development of new methods to increase PPM mechanical strength, such as microalloying, use of bisized feedstock, etc., has a great resource-saving potential. Advantages of developing new processes to form and consolidate PPMs from titanium powders are described, including: formation of a gradient porous structure by spark plasma, electric-discharge, selective laser, and microwave sintering and microinjection molding; modification of physicochemical and biochemical properties of PPM pore surface to change functional characteristics; creation of composite PPMs containing isotropically distributed target components such as activators, sorbents, reinforcing additives, etc. It is important to develop PPMs with anisotropic structural properties across the thickness and (or) the area of the porous element distributing a flow of gas or liquid.
Keywords: titanium powder; porous powder material; consolidation; forming; anisotropy of porous structure

Interaction of Chromium Carbide with a Kh13M2 Steel Matrix by R. V. Yakovenko; V. A. Maslyuk; A. A. Mamonova; A. N. Gripachevskii; N. I. Denisenko (644-650).
The paper examines the influence of sintering temperature in the range 1150–1300°C on interaction of chromium carbide Cr3C2 and a Kh13M2 steel matrix. It is shown that molybdenum actively participates in the interaction process, which leads to the formation of M7C3, M23C6, and M3C carbides even at 1150°C.
Keywords: steel matrix; chromium carbide; sintering; phase transformations; X-ray diffraction

Sintering of Cu–Sn–P–MoS2 Powder Samples at 780°C by A. G. Kostornov; O. I. Fushchich; T. M. Chevychelova; O. D. Kostenko (651-655).
The influence of initial porosity and MoS2 content of pressed Cu + 9Sn + 1.5P + (5, 10, 15%) MoS2 powder samples on their growth during sintering in hydrogen at 780°C is studied. The growth of samples with the same MoS2 content decreases with higher initial porosity and the growth of samples of the same size and same porosity after pressing increases with greater MoS2 content. Water vapors generated during the hydrogen reduction of oxides present on the starting tin powder and phosphorous-copper alloy powder cause swelling of the samples. Moreover, phase transformations in the material during sintering can increase the samples as new phases are formed (copper sulfide Cu2S) with a larger crystal lattice that that of the matrix and molybdenum disulfide.
Keywords: powder composition; sintering; temperature; growth; porosity; decomposition; oxides

High-Energy Electrospark Surface Strengthening of Steels with Composite Ceramics by I. A. Podchernyaeva; A. D. Panasyuk; D. V. Yurechko; A. M. Paramonov (656-662).
The surface and cross-sectional structure, composition, and microhardness of composite coatings on ShKh15 and R6M5 steels have been studied under high-energy electrospark deposition with electrode materials based on zirconium boride and titanium (zirconium) nitride. It is shown that mass transfer of doping components into a metallic substrate is determined by wetting of the refractory component by iron. The strengthening/softening of the steel substrate is ascertained under high-energy electrospark deposition.
Keywords: electrospark deposition; composite material; wear-resistant coating; coating deposition mechanism

Multifunctional Erosion-Resistant Gas-Diffusion Coatings on Steels by V. I. Zmii; S. G. Ruden’kii; N. F. Kartsev; V. V. Kunchenko; Yu. V. Kunchenko; E. V. Timofeeva (663-668).
Multicomponent coatings on 20 and Kh18N10T steels formed by the method of vacuum activated diffusion saturation are studied. A mixture of B4C, Al, Ni, Si, Cr, and C powders is used as the saturating medium. A thermodynamic analysis of reactions that accompany the titanizing process. Metallographic, micro-hardness, and X-ray diffraction data are discussed. The cavitation–erosion resistance of multicomponent coatings on steels is studied. It is established that these coatings improve the resistance of steel 20; the destruction rate being the same for both 20 and Kh18N10T steels.
Keywords: vacuum activated diffusion saturation; multifunctional coating; erosion resistance

Elaboration of C/C Composites Based on the Infiltration of a Hydrocarbon Precursor in Supercritical State into the Preform by L. Maille; A. Guette; R. Pailler; Y. Le Petitcorps; P. Weisbecker (669-673).
This paper reports on the development of a new process for the fabrication of a C/C composite for aeronautic and aerospace industries, in order to reduce the infiltration time of the carbon perform. The infiltration of a carbon fibrous preform by means of a hydrocarbon in the supercritical fluid state is done at high temperature in order to obtain a carbon matrix. The microstructure of the pyrocarbon coating is characterized by SEM and TEM. The experimental parameters (temperature, hydrocarbon pressure, residence time) are tuned in order to elaborate the carbon matrix. The best conditions lead to in-depth rapid densification from the top of the preform. After several experiments, the densification has been improved.
Keywords: supercritical fluid; chemical vapor infiltration; C/C composites

Effect of the Cooling Rate During Melt Solidification on the Structure and Properties of WC–W2C by I. Yu. Trosnikova; P. I. Loboda; O. P. Karasevska; O. I. Bilyi (674-679).
The paper examines the effect of cooling rate on the structure, phase composition, size of coherent scattering domains, and stress–strain state of relit commercially used to strengthen machine parts and mechanisms that perform under abrasive wear and high contact loads. Optical and scanning electron microscopy, quantitative X-ray diffraction, and electron microprobe analysis have been employed to reveal that higher cooling rates during melt solidification decrease the sizes of phase components in the 20 wt.% WC–80 wt.% W2C alloy and increase compressive stresses in the W2C matrix phase and tensile stresses in WC inclusions, improving the hardness of relit (by 1.5 times).
Keywords: tungsten carbide; cooling rate; stresses; hardness; grain-boundary strengthening mechanism

Fabrication of an Alumina–Copper Composite Using a Ceramic Preform by K. Jach; K. Pietrzak; A. Wajler; A. Strojny-Nedza (680-685).
In this work alumina preforms with an open porosity of 85 and 90% were produced by the replication method. The obtained preforms were used for the fabrication of Cu–Al2O3 composites. We analyzed the effect of applying pressure during a hot-pressing process on the microstructure and mechanical and thermal properties of the obtained materials. It was found that application of higher pressure (10 MPa) during sintering led to the destruction of the ceramic preforms. It facilitated filling of the remaining pores with copper, which resulted in a more homogeneous material with better mechanical and thermal properties.
Keywords: Cu–Al2O3 composites; hot-pressing process; ceramic preforms; microstructure; mechanical properties

Phase Equilibria During Solidification in the Ti–TiAl–DyAl2–Dy Region of the Ti–Dy–Al System by M. V. Bulanova; Yu. V. Fartushna; K. A. Meleshevich; A. V. Samelyuk (686-708).
Phase equilibria during solidification in the Ti–TiAl–DyAl2–Dy region of the Ti–Dy–Al system are studied by differential thermal analysis, X-ray diffraction, metallography, and electron microprobe analysis. The liquidus and solidus surfaces, vertical sections, and reaction scheme in the solidification range are presented. No ternary compounds are found in the studied composition range. It is shown that DyAl2 undergoes polymorphic transformation at ~1200°C. The αl and α2 phases that coexist only with solid phases in the binary Ti–Al system participate in equilibria with the liquid phase in the ternary Ti–Dy–Al system. The liquidus surface is characterized by the primary solidification fields of the phases based on βTi (β), high-temperature αTi (αh), lowtemperature αTi (αl), Ti3Al (α2), TiAl (γ), Dy2Al, Dy3Al2, DyAl, βDyAl2, αDyAl2, βDy, and αDy. The solidus surface has elven three-phase fields: β + (βDyAl2) + αl, (βDyAl2) + αl + α2, β + αh + (βDyAl2), αh + γ + (βDyAl2), (βDyAl2) + α2 + (αDyAl2), (DyAl) + (Dy3Al2) + (αDyAl2), (αDy) + β + αl, (DyAl2) + α2 + (Dy3Al2), (Dy3Al2) + α2 + (Dy2Al), α2 + αl + (Dy2Al), and αl + (αDy) + (Dy2Al). The first two fields result from invariant four-phase peritectic reactions, LP1 + β + (DyAl2) ⇄ αl and LP2 + αl + (βDyAl2) ⇄ α2 proceeding at 1130 ± 5°C and 1180 ± 7°C, respectively. The next eight three-phase fields result from invariant four-phase transition reactions: LU1 + β ⇄ αh + (βDyAl2) at 1325 ± 8°C, LU2 + αh ⇄ γ + (βDyAl2) at 1260°C, LU3 + (βDyAl2) ⇄ α2 + (αDyAl2) at 1060 ± 4°C, LU4 + (DyAl) ⇄ (Dy3Al2) + (αDyAl2) at 1010 ± 9°C, LU5 + (αDy) ⇄ β + αl at 970 ± 4°C, LU6 + (αDyAl2) ⇄ α2 + (Dy3Al2) at 960 ± 8°C, LU7 + (Dy3Al2) ⇄ α2 + (Dy2Al) at 955 ± 16°C, and LU8 + α2 ⇄ αl + (Dy2Al) at ~930°C. The three-phase αl + (αDy) + (Dy2Al) field results from an invariant eutectic process, LE ⇄ αl + (αDy) + (Dy2Al), at 910 ± 15°C. The two-phase region in the solidus surface has a temperature maximum at 1343 ± 5°C, corresponding to the invariant three-phase le1 ⇄ β + (βDyAl2) reaction.
Keywords: phase diagram; liquidus surface; solidus surface

The paper explains the mechanisms whereby components in the diamond–(Fe–Cu–Ni–Sn–CrB2) system and products of their interaction influence the micro- and nanostructure as well as mechanical properties of the composites sintered in molds in a muffle furnace followed by hot recompaction. The p–t parameters of hot recompaction that provide decarburization in the diamond–matrix transition zone by forming Fe3C, Cr3C2, Cr7C3, and Cr1.65Fe0.35B0.96 layers are determined. The wear resistance of these composites is three times as high as that of the samples produced from feedstock without chromium diboride.
Keywords: diamond; iron; copper; nickel; tin; chromium diboride; interaction; layer; transition zone; phase; composite; decarburization; structure; properties; wear resistance

Effect of 3D-Braided Structure on Thermal Expansion of PIP–Cf/SiC Composites by Deke Zhang; Yingbin Cao; Rongjun Liu; Changrui Zhang; Yanan Jiao; Chunlei Yan (722-726).
3D3d, 3D4d, 3D5d-braided Cf/SiC composites were fabricated by precursor infiltration and pyrolysis (PIP) with polycarbosilane as the matrix precursor. The coefficient of thermal expansion (CTE) of Cf/SiC composites was measured in longitudinal and transversal directions in the temperature range from –150°C to 25°C. The longitudinal CTE varies in the range (0.09–0.68) × 10–6/°C, and the transversal CTE varies in the range (0.21–1.95) × 10–6/°C. Various CTEs of 3D-braided Cf/SiC composites were mainly determined by different braided structures of carbon fibers. The longitudinal CTE is lower than transversal CTE for the negative axial expansion of carbon fibers at cryogenic temperature. Microcracks were examined to understand the effect of structure on the thermal expansion of composites.
Keywords: Cf/SiC composites; coefficient of thermal expansion; braided structure; carbon fibers; SiC