Effect of shell on the change in shape of a porous billet during isostatic pressing. 2. Main results

Isostatic pressing of porous ceramic material in a container is considered. Simulation of the process is based on flow theory with smooth potential. It is aimed at studying the shape change phenomenon. The effect of various factors including initial density and dimensions as well as rheological characteristics is considered. When the ceramic material approaches a rigidly-plastic condition and container material flow is controlled by a linear viscous mechanism shape change is more marked. Institute for Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 41–46, May–June, 1997.     

Physical principles and technological aspects of the production of gradient composites based on an oxygen-free ceramics

This article examines the technological aspects of producing a new generation of ceramic composites— functionally gradient materials. It is shown how a percolation model of the electrical conductivity of resistive systems that was modified by the authors can be used to predict the electrical and mechanical properties of composites with a high degree of accuracy. Gradient composites in conversion systems designed to convert an electrical energy into heat are used as an example to demonstrate the promise of the proposed method as a means of optimizing the processing regimes for the production of ceramic composites having the required level of electrical and mechanical properties. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 3–16, March–April, 1999.     

Effect of Surface Treatment with Concentrated Energy Fluxes on the Properties of Composite Materials Based on Silicon Carbide and Coatings Made from Such Composites

Based on a study of the structure and composition of the composite ceramic SiC - Al₂O₃ - ZrO₂, its tribomechanical properties and behavior in high-temperature corrosion, we recommend the material for use as sealing elements and for deposition of wear-resistant and corrosion-resistant coatings. We have studied the formation of gradient layers when the ceramic surface is modified with refractory titanium compounds TiN - TiB₂ (1:1) with an Fe(Ni) - Cr - Al undercoat using concentrated solar radiation and when the steel surface is modified with laser irradiation of the SiC - Al₂O₃ - ZrO₂ coats. We have shown that laser modification of steel by the silicon carbide-based composite increases its corrosion resistance by a factor of 4–5 at 800–900 °C. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 91–99, July–August, 2005.     

Wear Resistance of Plasma-Sprayed Coatings in Intensive Abrasive Wear Conditions

The abrasive wear resistance of plasma-sprayed oxide ceramic (Al2O3 and Cr2O3) and clad cermet ((Ti–Cr–C)–30% Ni and (TiC)–30% Ni) coatings was studied. The wear characteristics of the coatings such as wear rates, friction forces, friction coefficients, and wear groove depth determined with two methods were compared. The wear test methods included simulation of the friction process using loose abrasive particles and reciprocal ball-on-disk friction using a diamond indenter. The plasma-sprayed TiC-based coatings showed the lowest wear rate and can be applied to protect equipment parts subjected to intensive abrasive wear. The wear loss of the (Ti–Cr–C)–30% Ni and (TiC)–30% Ni coatings determined by friction against loose abrasive particles was 10–17 μm, while the wear loss of the oxide ceramic coatings was 20–42 μm, being 2–2.5 times higher on average.     

Powder metallurgy industry and managerial economics

The phase composition and structure of two-layer thermal-barrier metal-ceramic coatings applied by electron-beam vapor deposition in one process cycle are investigated. It is shown that the outer ceramic layer has a two-phase (monoclinic-tetragonal) structure and is characterized by an axial growth texture of columnar crystallites with prevailing <001> orientation. High-temperature isothermal annealing in an oxidizing medium increases the amount of the tetragonal constituent in the outer ceramic layer of the thermal-barrier coating. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 7–8 (456), pp. 100–106, 2007.     

Synthesis and physicomechanical properties of B4C-VB2 composites

We have studied the properties of composites in the B₄C-VB₂-C system, obtained by reaction synthesis with hot pressing. We have established that the presence of free carbon and vanadium boride in the ceramic makes it possible to activate the sintering process and to obtain a dense, highly dispersed ceramic with good structural homogeneity parameters for lower isothermal holding temperatures. The composite ceramic has higher hardness and bending strength over a broad range of vanadium boride content than the monophase ceramic based on boron carbide. The strength properties of the composite ceramic containing up to 8 vol.% vanadium boride are improved by means of a mechanism involving propagating cracks bending around obstacles. When the VB₂ concentration increases further, the properties of the composite are determined by a microcracking mechanism. In this case, we observe relatively small changes in the elastic characteristics, which depend linearly on the composition of the ceramic. Introducing vanadium boride into the material is also accompanied by an increase in the contact and microstructural strengths. The results obtained indicate that the new composite material is promising for fabricating wear-resistant and shock-resistant components of various structures and machines. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 59–72, January–February, 2006.     

Physicochemical Processes of Fabricating Ceramic Materials Based on Nanopowders of Zirconium,Yttrium, Cerium,and Aluminum Oxides

When studying nanoceramics, it is necessary to constantly keep in mind the closest interrelation of their fabrication method, structure, and properties. Nanoceramic materials are used in various branches of technology as structural and functional materials. Nanoceramics are also widely used in medicine. They are harmless, stable, and have great affinity to living organisms. ZrO2-based nanoceramics have a lower elastic modulus than other oxide materials. The specificity of their application lies in their high rupture strength, thermal shock resistance, and chemical stability at high temperatures. However, it is necessary to solve the problem of increasing the fracture toughness of ZrO2-based ceramic materials. The complex alloying of ZrO2 with yttrium and cerium oxides and the use of the Al2O3 additive leads to an increase in the fracture toughness and lowering of the negative effect of materials in the biological medium. In this work, the physicochemical properties of ceramic powders and materials of the ZrO2–2Y2O3–4CeO2–Al2O3 system synthesized by the chemical deposition of inorganic precursors when applying the sol-gel technology are considered based on scientific data and experimental studies. Alloying pure zirconium oxide by stabilizing Y2O3 and CeO2 oxides and thermal hardening of Al2O3 ensure the conservation of the tetragonal structure at room temperature, which makes it possible to retard and control the crack resistance of the material under the load. Investigations into the influence of the sintering temperature and aluminum oxide content on the microstructure and grain size, as well as physicomechanical properties of ceramic materials of compositions ZrO2–2Y2O3–4CeO2 + 1 wt % Al2O3 and ZrO2–2Y2O3–4CeO2 + 3 wt % Al2O3, are carried out.     

Current state of development of new ceramic materials (review of foreign literature)

The current state of development of advanced ceramic materials abroad is reviewed. The volume of production of powders and parts from advanced ceramics in the world, North America, Japan, and Western Europe for 1989–1995, and the structure of their application are shown. Prospects for advanced ceramics development up to the year 2000 are discussed. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 101–113, January–February, 1999.     

Application of conducting Si3N4 composites in wide-range electric radiators. III. Load life of ceramic radiators

Data from the literature and our own results are used to analyze the load life of non-oxide ceramic electric radiators. Silicon nitride ceramic radiators operating in the thermal cycling mode are shown to have a load life of more than 2000 on-off cycles. The load life correlates with the magnitude and sign of the temperature resistance coefficient (TRC) of the resistive layer of the functional composite. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 50–54, July–August, 1998.     

Production of high-strength tubes made of steels of type 15GFB

A unit for making L-class high-strength pump-compressor tubing composed of low-carbon, low-alloy steels of type 15GFB is now being used on the 140 mill in the tube-rolling shop at the Rustavi Metallurgical Plant. The steel 15GFB pump-compressor tubing made by the technology that was developed has the following service properties: σ_y = 630–670 N/mm², σ_u = 730–780 N/mm², δ = 18–22%, ψ = 55–60%, KCU = 1.6–2.2 MJ/m². The percentage of ductile fracture at room temperature is 85–95%. __________ Translated from Metallurg, No. 1, pp. 79–80, January, 2006.     

Tribotechnical properties of a composite of a metal-ceramic system

The paper reports the results of tribotechnical tests of a metal matrix based on a copper-nickel alloy with a tin-lead solid lubricant additive which contained varying amounts of the ceramic binary alloy B₄C+ZrB₂. The tests showed that the presence of a refractory phase in the metal matrix greatly enhanced the Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 54–58, July–August, 1998.     

High-temperature oxidation of composite AlN-ZrB2-ZrSi2 ceramics

The high-temperature (to 1450°C) oxidation of AlN-ZrB₂-ZrSi₂ powders and compact ceramic materials with different contents of ZrB₂-ZrSi₂ solid solution in air is examined using scanning electron microscopy and differential thermal, thermogravimetric, x-ray phase, and x-ray spectrum microanalyses. It is established that the hot-pressed (practically porousless) ceramic materials have high corrosion resistance up to 1350–1400°C when scale components (individual oxides) interact with each other to form solid solutions based on aluminum oxide, zirconium oxide, and aluminum borate. These phases become sintered in the presence of the liquid B₂O₃ phase, self-reinforced scale being formed. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 196–203, 2008.     

X-ray spectral investigation of the electronic structure and chemical bonding in ultradispersed powders and the fine-grained materials obtained from them. I. Titanium nitride

The dependence of the electron energy spectrum of ultradispersed TiN powders on particle size was studied by the method of ultrasoft x-ray spectroscopy. A relative narrowing of the x-ray TiL_α and NK_α emission bands (which reflect the energy distribution of valence Np- and Tid-states) depended on the specific surface area of the powders and charge states of the Ti and N atoms. It was shown that narrowing of these bands is due to localization of the Np- and Tid-orbitals of surface atoms as a result of breaking Ti−N bonds. Broadening of the NK_α and TiL_α bands in certain energy ranges was observed after compacting ultradispersed powders. This is a result of Tid and Np orbital splitting caused by the formation of Ti−N bonds between the surface atoms of neighboring particles brought into contact at high pressure and temperature. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 75–85, July–August, 1999.     

Production of high-carbon steel in the open-hearth shop at the MMK

This article describes several variants for carbonizing steel. It is preferable to carbonize steel with a carbon-bearing material in lump form (5–20-mm fraction) as the steel is tapped from an arc steelmaking furnace. Comparative results are presented on the quality of continuous-cast semifinished products obtained with the use of different variants of the carbonization technology. N. N. Shakirov, A. N. Buzin, and O. A. Nikolaev also participated in this study. __________ Translated from Metallurg, No. 1, pp. 41–42, January, 2007.     

Improving the technology for making tubes of corrosion-resistant steels

A new energy-and metal-saving technology has been proposed for making commercial and conversion tubes of corrosion-resistant steel from centrifugally cast semifinished products. Technical solutions that were found allow the tubes to be extruded with a high degree of accuracy while minimizing the consumption of metal. Trial extrusion of tubes from a centrifugally cast semifinished product confirmed that ductility properties are increased by a factor of 3.5–4 (δ ≥ 40%, ψ ≥ 45%), which means that it is possible to cold-roll even tubes made of low-ductility corrosion-resistant foundry steel 20Kh25N20S. __________ Translated from Metallurg, No. 5, pp. 60–62, May, 2007.     

Crack resistance of modern ceramics and ceramic composites. II. EF method

The procedure and test results are for crack resistance are presented for various monolithic and composite oxide and nonoxide ceramics by chipping the rectangular edge of a polished specimen. The main difference of the test method suggested (EF method) with an arbitrary point of fracture for a specimen edge from the well-known similar method with a fixed point of fracture is demonstrated. Tests are performed with Rockwell, Vickers and Knoop indenters, and the Rockwell indenter is chosen as the optimum. On the basis of statistically reliable experimental data a direct relationship is established between edge toughness and critical fracture toughness determined in the same ceramic specimens based on scandium oxide, aluminum oxide, zirconium dioxide, silicon carbide and silicon nitride. The EF method, whose use does not require special equipment, may be used effectively in a normal metallurgy test laboratory, particularly when specimens for evaluating ceramic breaking resistance may only be prepared in smaller sizes than those required for standard crack resistance tests. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 39–49, July–August, 2006.     

A New Rhombic Approximant in the Al - Pd - Fe System

Scanning and transmission electron microscopy have been used along with x-ray diffraction in the Al - Pd - Fe system to establish a new type of B-centered rhombic N phase. The lattice constants of the N phase are as follows: a = 2.31 nm, b = 1.60 nm, and c = 4.70 nm. Electron-probe microanalysis establishes the composition: Al_76.6Pd_10.0Fe_13.4. Differential thermal analysis indicates that the N phase melts incongruently at a temperature close to 885°C. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 94–99, May–June, 2005.     

Effect of the reductions made during cold reduction on the structure and properties of steel 01YuT

Conclusions  

New functionally gradient materials in the Ti−Si−C system

A new ceramic functionally gradient material (FGM) with controlled hardness and fracture toughness is presented. Very hard SiC and soft, fracture resistant Ti₃SiC₂ ceramics were manufactured as one multilayered composite. This composite was prepared by hot-pressing from SHS-derived powders. Microstructure and indentation tests proved the FGM structure. Mining and Metallurgy University, Krakow, Poland. Published in Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 42–45, March–April, 1999.     

Composites with a functional gradient in the systems Si3N4−Al2O3−Y2O3−TiC

Composites with a functional gradient in the system Si₃N₄−Al₂O₃−Y₂O₃−TiC were made by laminating and sintering ceramic films obtained by tape casting. The films had high contents of TiC and Al₂O₃ and were of different thicknesses. Materials with a high density and high fracture toughness (K_1c≈9.3 MPa·m^1/2) were obtained. Warsaw Polytechnic Institute. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 1–7, July–August, 1999.