Fatigue and Compression Characteristics of Al 6061–B 4 c Composite Materials

Aluminum matrix composites reinforced with boron carbide are a kind of materials that are widely used because of high strength, low density, and improved tribological properties. In this study, mechanical properties of Al 6061–B4C composites reinforced with B4C of three different particle sizes were investigated. In the Al 6061–B4C composite materials, produced by the powder metallurgy methods (extrusion of billets obtained by sintering at temperature of 550°C under pressure of 450 MPa), the change of mechanical properties such as hardness, compressive strength, and fatigue life, related to B4C particle size and the applied heat treatment mode (aging at 180°C for 5 h), were investigated. The hardness of the materials is increased with B4C grain size and the heat treatment. After the heat treatment, the fatigue life of Al 6061–B4C (3 μm) material increases slightly, while that of the composite materials decreases with larger size of B4C reinforcement. The fatigue life of the composite materials reinforced with a larger grain size B4C is reduced by heat treatment. While the compression test data of untreated composite materials were similar to each other, the heat treatment increased these values in all samples. The highest increase in the compression strength was observed in the composite reinforced with 17 μm sized B4C. The addition of graphite reduces the deformation ability of the composites.     

Properties of plasma-deposited composite metal-boron nitride coatings

Conclusions By altering the processing parameters of plasma spray-deposition of composite metal-boron nitride materials, it is possible to vary within wide ranges the physicomechanical properties of soft sealing deposits of these materials. The strength, porosity, hardness, and solid lubricant content of metal-boron nitride sealing coatings are determined primarily by the physicomechanical properties of the metal and the amount of boron nitride in the composite being deposited and also by the particle size analysis of the charge. The effect of jet parameters on the properties of coatings varies depending on the nature of the composite material, which is mainly due to differences in the energetic levels and degrees of spheroidization of charge particles.Translated from Poroshkovaya Metallurgiya, No. 8(224), pp. 91–96, August, 1981.     

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.     

Tribological Properties of Composite Materials Based on Refractory Titanium Compounds

The tribological properties have been examined for composite materials based on binary titanium-chromium boride and titanium nitride under conditions of dry friction over a wide speed range (1–25 m/sec). The materials have good tribological properties, which exceed by almost an order of magnitude those of known materials. Specifications are formulated for materials promising for high-speed friction units. A necessary condition for viability in high-speed friction units is high strength of the adhesion between the films of oxidation products, and another is low tendency for adhesion with the counterbody. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 58–64, July–August, 2005.     

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.     

Corrosion behavior of zirconium diboride-based ceramics and electrospark coatings in 3% NaCl solution

The paper examines the corrosion behavior of AlN-ZrB₂, AlN-TiN, and ZrB₂-LaB₆ composite materials and associated electrospark coatings based on aluminum alloy AL9 in 3% NaCl solution. It is shown that the electrochemical corrosion resistance of composites is close to that of titanium nitride. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 54–57, 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.     

六方氮化硼(hBN)表面镀镍对Ni-Cr/hBN固体自润滑材料性能的影响

为了改善六方氮化硼(hBN)固体润滑剂和Ni-Cr合金基体之间的润湿性,采用硝酸镍分解-氢还原法制备Ni包覆hBN粉末(即Ni/hBN粉末).分别用Ni/hBN粉末和未包覆的hBN粉末作为固体润滑剂制备(Ni-Cr)/hBN自润滑复合材料,研究hBN粉末表面包覆Ni对该复合材料组织和性能的影响.结果表明:与hBN相比,...     

Conditions for preparing large blanks of hexanite-R and their properties

Sintering of pure wurzitic boron nitride [99% (wt.) BN_w] was performed under high static pressure at high temperature (P=8–9 GPa, T=1700–2000 K). The “double toroid” equipment is used at high pressure. Compact single- and two-layer plates 14–15 mm in diameter are fabricated. It is shown that sintering of BN_w is accompanied by the phase transformation BN_w→BN_sp (cubic boron nitride). The phase composition, microstructure, density, Young’s modulus, and wear resistance during cutting are also studied. It is found that sintered materials have the same physical and chemical properties as the well-known superhard material Hexanite-R but due to the larger blank dimensions there are greater cutting possibilities. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1-2, pp. 55–63, January–February, 1998.     

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.     

Optimizing Wear Resistance via Brazing Temperature Adaption: Application into CBN/Cu-Sn-Ti Composites

Metallurgical and Materials Transactions B - Cubic boron nitride (CBN)/Cu-Sn-Ti composites as potential superabrasive products are prepared. It is found that as the temperature increases, porosity...     

Dependence of the Structure of Sintered Boron Carbonitride on the Defect Level in the Starting BN Powder

We have carried out a comparative x-ray analysis of boron nitride powders with different degrees of ordering and sintered specimens of boron carbonitride based on such powders. We have established that an indicator of sintering activity for the boron carbonitride specimens is the rate of formation of the r-BN phase, the content of which depends on the degree of ordering of the starting BN powder. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 100–107, May–June, 2005.     

High-temperature friction of refractory compounds

The paper overviews long-term studies into the behavior of metallic (carbides, borides, and nitrides of transition metals), and nonmetallic (boron and silicon carbides, aluminum nitride) refractory compounds as well as composite materials based on them in high-temperature friction in vacuum and air. The friction characteristics (wear rate and friction coefficient) are indicated as a function of temperature in the range from room temperature up to 1000–1400 °C. Data of x-ray examination and electron microscopy of friction surfaces are cited. The fracture mechanism for contacting surfaces of materials in friction is considered. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 167–178, 2008.     

Application of SHS for the production of porous powder permeable composite materials of titanium—Titanium nitride

The fabrication of a porous powder permeable composite material (PPPM) of titanim—titanium nitride by the method of self-propagating high-temperature synthesis (SHS) was investigated. The effect of particle size, porosity, and nitrogen pressure on the properties of the material were determined experimentally. Theoretical calculations of the optimal process parameters (adiabatic combustion temperature and effective depth of nitrogen penetration) were carried out. The SHS method produces a PPPM consisting of a framework of titanium particles coated with titanium nitride, which possesses a high melting point, thermal and electrical conductivity, and chemical stability. Scientific Research Institute for Powder Metallurgy, Minsk. Translated from Poroshkovaya Metallurgiya, Nos. 5/6(395), pp. 75–80, May–June, 1997     

Development of a Method for High-Temperature Shock Compression of Powder Mixtures to Obtain Cubic Boron Nitride

We used shock compression of a mixture of boron nitride powder with an alkali halide salt as an additive to realize the phase transformation of turbostratic BN to the cubic modification. We have experimentally studied the effect of the type and amount of the additive and also the initial density of the mixture on the yield of the cubic phase of BN. We have roughly calculated the pressure and temperature arising upon shock compression of powder mixtures in an annular cylindrical storage ampul. We have shown that melting of the additive has a substantial effect on development of the phase transformation in boron nitride under shock loading conditions. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 107–118, July–August, 2005.     

Production by various methods of composite materials based on a hard metal with cubic boron nitride

Conclusions During the production of the composite materials under consideration by orthodox sintering the cubic boron nitride and hard metal react with each other, with the formation of borides and appearance of porosity as a result of the evolution of gaseous reaction products, and the strength of the materials is therefore low. During hot pressing the reaction between the components of the CBN-containing materials is less intense because the sintering temperature is lower and the holding time shorter, but the strength of the resultant materials remains comparatively low. The most promising method of obtaining composite CBN-containing materials exhibiting high abrasive ability in the grinding of hard and brittle materials is shock sintering.Translated from Poroshkovaya Metallurgiya, No. 3(243), pp. 43–45, March, 1983.     

Adsorption-chemical activity and interaction in the boron nitride-titanium hydride system

The paper examines the effect of physicochemical properties of starting boron nitride and titanium hydride on their reactive activity in the synthesis of the TiN-TiB_x composite. There are kinetic data on thermal desorption of the active adsorbate from the BN surface, which precipitated from the gas mixture (20 vol.% O₂-80 vol.% N₂ under the relative humidity of 80%). Kinetics of hydrogen release from titanium hydride in isothermal conditions and controlled rate of temperature increase in the reactive system is researched. A possible mechanism of chemical transformations of starting compounds and synthesis of the TiN-TiB_x composite is considered. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 102–110, 2007.     

Stainless-steel porous-layered and framework fiber-powder composites

Porous layered and framework composites have been made from stainless-steel fibers and powders in the form of sheets. Measurements have been made on the electrical conductivity, elastic modulus, and ultrasound speed as dependent on the porosity, fiber and powder dispersions, and the structural features of the composites. Framework composites are better than layered ones throughout the porosity range, while purely fiber materials are better with porosity less than 60%. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 45–50, January–February, 2006.     

Deformation behavior of skeletal composites under mechanical loading

The deformation behavior of ceramic-metal composites with a bulk-linked metal skeleton made of highly porous cellular nickel and a stainless wire mesh is examined. It is established that samples of skeletal ceramics remain intact after all types of destructive tests and show high plasticity and strain and fracture energies. A technique is developed for producing ceramics with a bulk-linked metal skeleton by filling a highly porous framework with a ceramic powder and subsequent pressing and sintering of the composite. The technique is tested for two types of skeletal ceramics: structural ceramics such as pyroceramics-highly porous cellular nickel and bioceramics such as hydroxyapatite-highly porous stainless wire skeleton. The hydroxyapatite-based composite has lower bending strength and shock bending energy but higher plasticity and nondestructability than the pyroceramics-based composite. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 7–8 (456), pp. 82–90, 2007.     

Aluminum matrix composites: Fabrication and properties

Aluminum alloy matrix composites containing 1 to 30 wt pct of fibrous and particulate nonmetals varying in size from 0.06 μm to 840 μm were fabricated. The composites were cast into cylindrical molds for friction and wear tests, hot extrusion and tensile tests. The distribution of the nonmetals in the cast ingots was homogeneous. Friction and wear tests were done on a pin (52100 bearing steel) and dish type machine without lubrication. It was found that composites containing ∼10 wt pct or more of SiC, TiC, Si₃N₄, Al₂O₃, glass, solid waste slag, and silica sand wear less than the pure matrix alloy, but have slightly higher average coefficients of friction. Wear in composites containing soft particles, especially MgO and boron nitride was higher than the pure matrix alloy. The average coefficient of friction of all the composites was in the range of 0.35 to 0.58. Increasing the sliding velocity reduced this range to ∼ 0.4 to 0.45. The longitudinal tensile properties of the extruded composites (with the exception of loss of ductility in some cases) are comparable to that of the matrix alloys. Improvements in strength or ductility were noted. For example, addition of 15 wt pct of 3 μm size Al₂O₃ particles raised the yield and ultimate strength of the Al-4 pct Cu-0.75 pct Mg alloy matrix from 227 to 302 MPa, and 356 to 403 MPa, respectively. The corresponding percent elongation decreased from 25.8 to 12.5. The fact that the various composites can be readily cast and hot formed suggests a variety of engineering applications. AKIRA SATO, formerly Visiting Scientist at Massachusetts Institute of Technology, Cambridge.