Behavior of multilayer steel-bronze composites on frictional loading

Tribological aspects are examined for layered composites made by consolidation. Dry friction tests at sliding speeds of 1.6–4.3 m/sec show that this multilayer antifriction material is better by 1–2 orders of magnitude in wear resistance than the initial material. The multilayer composite can withstand a load increased by an order of magnitude without losing its viability under the conditions of surface-structure adaptation. Deceased. Translated from Poroshkovaya Metallurgiya, Nos, 1–2(411), pp. 38–44, January–February, 2000.     

Sintering behavior and strength properties of stomatological porcelain—Titanium nickelide composite materials

The sintering behavior and strength properties of stomatological porcelain—titanium nickelide composites were investigated. The dependence of porosity, linear and volumetric changes, phase composition and structure on sintering time and temperature, component concentrations, and initial porosity have been determined. It was shown that density changes are the result of a competition between shrinkage and volumetric growth. An optimal regime of sintering to ensure open porosity and high strength is recommended. Siberian Physico-Technical Institute, Tomsk. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 31–36, July–August, 1998.     

Correcting for container temperature inhomogeneity in sintering diamond-metal composites

A model is used for thermal conduction in a homogenized medium to calculate the temperature field in a container enclosing diamond-metal composites. The temperature pattern and porosity of the sintered materials have been determined for various values of the heat-transfer coefficient of the oven (0.01–0.1). The results obtained for β=0.03 are compared with experiment. The calculated porosity agrees well with experiment. Superhard Materials Institute, Ukraine National Academy of Sciences Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 86–92, January–February, 1999.     

Structure and high-temperature strength of composite materials based on boron nitride

The structure and physicomechanical properties of composite materials based on boron nitride within which new phases (mullite and sialon) form during hot compaction are studied. It is established that the microstructure of composites is specified by their texture formation caused by the crystal morphology of boron nitride particles and it is almost independent of composite phase composition. It is shown that the main factor that affects strength is porosity. The dependence of strength on porosity is exponential in character. The strength of boron nitride-mullite and boron nitride-sialon composites is 110–140 MPa and at 20–1200°C it is almost unchanged. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 33–39, May–June, 2006.     

Densification and structure formation in the sintering of composite materials based on nitrides of the IV–V group transition metals. III. Sintering of composite materials in the (VN, TaN)—Cr systems

An investigation was made of densification and structure formation in composite materials in the systems (VN, TaN)—Cr during sintering in argon. It was shown that the shrinkage of these materials during liquidphase sintering is insufficient to provide dense composites (residual porosity was 35–40%). This is attributed to the low thermodynamic stability of VN and TaN, and the rapid evolution from these of nitrogen which accumulates in closed pores. Processes of heterodiffusion and alloy formation also have a negative effect on densification. Exchange reactions between chromium and the nitride-forming metals lead to the formation of a large quantities of intermetallics which embrittle the composite materials. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 13–18, January–February, 1999.     

Thermal conductivity and thermal expansion of graphite fiber-reinforced copper matrix composites

The high specific conductivity of graphite fiber/copper matrix (Gr/Cu) composites offers great potential for high heat flux structures operating at elevated temperatures. To determine the feasibility of applying Gr/Cu composites to high heat flux structures, composite plates were fabricated using unidirectional and cross-plied pitch-based P-100 graphite fibers in a pure copper matrix. Thermal conductivity of the composites was measured from room temperature to 1073 K, and thermal expansion was measured from room temperature to 1050 K. The longitudinal thermal conductivity, parallel to the fiber direction, was comparable to pure copper. The transverse thermal conductivity, normal to the fiber direction, was less than that of pure copper and decreased with increasing fiber content. The longitudinal thermal expansion decreased with increasing fiber content. The transverse thermal expansion was greater than pure copper and nearly independent of fiber content. formerly with NASA Lewis Research Center, is retired David L. McDanels, This article is based on a presentation made in the symposium “High Performance Copper-Base Materials” as part of the 1991 TMS Annual Meeting, February 17–21, 1991, New Orleans, LA, under the auspices of the TMS Structural Materials Committee.     

Effects of preparation technique for MK-5 material on frictional and wear response

A study has been made on how the method of making a tribotechnical material affects the frictional and wear behavior. The materials have been made from identical initial powders, which corresponded in composition to standard MK-5 powder material, but different methods were used: traditional sintering under pressure and plasma spraying. The tribological properties of material made by plasma spraying are better than those of ones made by the traditional method, because of the presence of oxides formed during the spraying. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 44–47, January–February, 2000.     

A percolation approach to conductivity dependence on porosity

The percolation approach is used in an analytic relationship between the electrical conductivity and the porosity, which represents a combination of equations previously proposed by Skorokhod for determining the porosity dependence of the electrical conductivity and the relative linear size of the contacts. Equations proposed by the authors use the shaking porosity as the most stable characteristic. The dependence gives better agreement with experiment than do certain analytic relationships given by others. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 16–21, May–June, 2006.     

Preparing hard-alloy mixtures in a magnetic induction rotor

The parameters have been optimized in welding titanium carbide powder for the preparation of TiC-Ni-Mo and WC-Co hard-alloy mixtures. The equipment enables one to accelerate the processing of the TiC-Ni-Mo hard-alloy mixtures to give a processing time of 1 hour subject to a given composition and average particle size of 0.8 μm. The major properties of specimens made from the mixtures are no worse than those of industrial analogs made by standard methods and in certain cases are better than them. Fine-Chemical Technology Institute, Moscow. Translated from Poroshkovaya Metallurgiya, Nos. 5-6(395), pp. 81–84, May–June, 1997.     

Selective laser sintering. I. Principles, continual model

he main thermophysical and rheological processes accompanying selective laser sintering are considered. A mathematical model of laser sintering is proposed. The results of computer experiments with the model applied to multilayer composites containing titanium nitride, diboride and carbide, as well as molybdenum, nickel, and steel are discussed. It is shown that densification depends on the heating regime and initial porosity of the composites. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 16–26, July–August, 1998.     

Investigation of a wear-and corrosion-resistant coating of the TiCN−Ni-alloy system, obtained by high-speed gas-flame spraying

The structure and properties of high-speed gas-flame (HSGF) coating of the system TiC_0.14N_0.86−Ni(CrBSi)-alloy (70%) on high-strength cast iron have been studied. The HSGF coatings were deposited on the Struya installation at the Institute for Problems of Materials Science, operating on an oxygen-hydrogen fuel mixture in a nearly stoichiometric ratio. The pressure in the combustion chamber was 0.6 MPa, the gas consumption was 8.5 g/sec, the sprayed powder consumption was 2.2 g/sec, the transporting air consumption was 0.5 g/sec, and the spraying distance was 200 mm. The coating was about 1 mm thick with a porosity of less than 2% and had a typical layered structure. The alternating zones were enriched with a refractory phase or metal. In comparison with the alloy WC (8% Co) the coating had lower linear wear (<5 μm/km) and a lower friction coefficient (0.1), and its resistance to high-temperature corrosion was almost an order of magnitude higher. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 40–44, July–August, 1999.     

Developing and mastering a technology for making steel with a sulfur content no greater than 15 ppm

The converter shop at the Azovstal’ combine has developed and successfully introduced a technology for making steel that contains no more than 15 ppm sulfur. The combine has already produced commercial batches of tube steel with a maximum sulfur content of 6–15 ppm. Reducing carbon content from 0.10–0.12 to 0.07–0.08% and lowering sulfur content from 40–70 ppm to 6–15 ppm have improved the quality of the metal of the slabs and rolled products made by the combine. Among these improvements: a decrease in axial porosity and axial segregation in the slabs, an improvement in the ductility characteristics of the rolled metal, a reduction in the degree of contamination of plate metal by nonmetallic inclusions, and a decrease in the incidence of plate rejection in ultrasonic tests. __________ Translated from Metallurg, No. 3, pp. 46–49, March, 2006.     

Influence of the structure on the elastic modulus of highly porous copper-based materials

The effect of the structure on the elastic modulus of two groups of highly porous sintered copper-based materials (foam and fiber metal) with 40 to 90% porosity is investigated. The elastic modulus of the materials is described within the sphere-rod model developed for foam plastic with an open porosity; the model uses an equation containing a structure parameter. Translated from Poroshkovaya Metallurgiya, Nos. 3/4(412), pp. 79–83, March–April, 2000.     

Effect of fiber volume fraction on the fracture behavior of Nb-1 Wt pct Zr/218W composites at elevated temperatures

Nb-1 wt pct Zr/218W long-fiber composite monotapes, nominally containing 0 to 70 vol pct of 218 tungsten fibers, were fabricated by arc spraying the Nb-1 pct Zr matrix onto the tungsten fibers. The monotapes were consolidated by hot pressing and hot isostatic pressing techniques. Tensile tests conducted between 1400 and 1600 K, under engineering strain rates varying between 1.5×10⁻⁵ and 1.5×10⁻³ s⁻¹, demonstrated that composites containing 70 vol pct of fibers had the highest strength-to-density ratio. Microstructural observations of specimens tested at 1400 K revealed that composites containing less than 50 vol pct of fibers showed extensive matrix cavitation, fiber-matrix debonding, and necking of the fibers. Above 50 vol pct, the composite matrix was less prone to cavitation, with an increasing tendency toward shear deformation of the fibers as the fiber volume fraction increased. No fiber damage was observed at 1400 K away from the fractured end, but significant fiber damage was observed at higher temperatures. A phenomenological model is presented to rationalize these observations. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee.     

Degradation of residual strength in SCS-6/Ti-15-3 Due to fully reversed fatigue

Little attention has been given to residual strength degradation in titanium matrix composites (TMCs) after exposure to fatigue loading. To address this problem, fatigue tests on SCS-6/Ti-15-3 were performed to investigate the fatigue life and residual strength behavior of TMCs with different fiber volume fractions. Results indicate that fiber volume fraction seems to have an effect on both of these quantities. Lower fiber percentages result in a material where the characteristics of the matrix, such as hardening or cracking, play a much larger role in the composite response. Fatigue lives were not affected by fiber volume fraction at higher strain ranges, but lower fiber volume fractions resulted in shorter fatigue lives at lower strain values. Also, a slight increase in residual strength occurred up to 75 pct of fatigue life, for the lower-fiber volume fraction material. Despite these distinctions between specimens with different fiber contents, all specimens tested retained the majority of their strength prior to failure. This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee.     

Reduction Extraction Method for Determining the Enthalpies of Decomposition Reactions of Different Boron Nitride Modifications

Pulsed (7–10 sec) reduction extraction in a helium gas carrier stream has been used for the first time to determine the standard enthalpies and the internal energies of thermal dissociation reactions for various modifications of boron nitride (BN) with and without carbon. The temperature dependences of the weight content of nitrogen extracted from nanosized (4–10 nm) and microsized (<1; 4–5 μm) BN powders in the range 2100–4000 K with a step of ~200 ± 25 K have been established. Nitrogen extraction from layered BN modifications (graphene and graphite structures) begins at 2400–2500 K and reaches 100% at 3500 K. The thermal decomposition curve for nanoand micropowders of dense BN modifications (wurtzite and sphalerite structures) is similar to that for the layered modifications and is shifted toward the high-temperature region by 900 K. The standard enthalpies of decomposition reactions for different BN modifications have been determined: 231 kJ/mole for graphene-like, 249 kJ/mole for graphite-like, 296 kJ/mole forwurtzite-like, and 391 kJ/mole for sphalerite-like modifications.     

Effects of a solid lubricant and technological parameters on the friction, wear, and mechanical properties of a composite based on polytetrafluoroethylene powder

Mathematical experiment planning methods have been applied to the effects of solid molybdenum disulfide lubricant content and those of technological parameters (content of special carbon fiber, preliminary size reduction time, and composite mixing time) on the antifriction and other mechanical properties of composite materials based on polytetrafluoroethylene and carbon fiber. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 21–32, May–June, 2006.     

Combustion synthesis of Ni3Al and Ni3Al-matrix composites

The self-propagating mode of combustion synthesis (SHS) of Ni₃Al starting from compacts of stoichiometrically mixed Ni and Al powders readily forms fully reacted structures with about 3 to 5 pct porosity, if green density of the compacts is greater than about 75 pct of theoretical. SHS-produced Ni₃Al matrix composites with up to 2 wt pct A1₂O₃ whiskers also have relatively low porosity levels. Porosity increases rapidly with lower green densities, higher Al₂O₃, or SiC whisker contents, and the degree of reaction completeness diminishes. The SiC whiskers undergo reaction with the matrix, while Al₂O₃ whiskers are nonreactive. All of these observations correlate well with temperature measurements made during the course of the reaction. The SHS mode can be achieved with agglomerated particle size ratioD _Al/D _Ni ≥ 1, larger than the limit established from studies of the thermal explosion mode of combustion synthesisD _Al/D _Ni ≃ 0.3. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

Production of parts with lengthwise grooves by pressing the working elements of a tool into the body of a compact

The technology of heat forming of powder products with lengthwise grooves has been developed, which consists of pressing the working elements of a tool in the body of a preheated porous blank. The influence of porosity, shape, the degree of preliminary plastic deformation, and the geometric parameters of the porous blank on the area of the textured zone of product lugs has also been examined. The maximum values are attained when blanks with a porosity of 15% (without preliminary compression) and 20–25% (with compression) are used. Novocherkassk State Technical University. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 113–117, July–August, 1998.     

Effect of compressive stresses on deformation and contact phenomena in pressed fibrous materials during sintering

A study is made of the processes that control deformation and contact phenomena in porous fibrous metallic materials. It was established that sintering of fibrous materials which are subjected to small compressive stresses in the pressing direction makes it possible to completely suppress the volumetric growth of specimens, which is seen during pressing and sintering. Due to the reestablishment of interparticle contacts, the resulting specimens have a significantly higher level of mechanical properties. For example, the ultimate tensile strength of the specimens is increased by a factor of 1.5–2 compared to control specimens of the same porosity. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 29–34, January–February, 2000.