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.     

Physicomechanical properties of galvanic chromium coatings on steel parts

The physicomechanical properties of galvanic chromium coatings on steel parts are studied. Mechanical treatment of a base and a coating by various finishing methods is shown to change the physicomechanical properties of the coatings.     

Effect of pulse duration and size of interelectrode interval on electric-spark spraying. I. Effect of pulse duration and size of interelectrode interval on rate of electric-spark transfer

The influence exerted by electric-spark spraying on the kinetics of mass transfer and the physicomechanical properties of coatings is investigated. It is shown that electric-spark spraying is determined by the dynamic properties of the cathode jets, which depend on the electrical parameters of the spark discharge, the size of the interelectrode interval, and the physical properties of the coatings, which vary during spraying.     

NiCrAl/ 膨润土阻燃封严复合涂层的 制备对钛合金基体性能的影响

NiCrAl/膨润土是一种可用于航空发动机的中高温封严涂层材料,同时具有一定的阻燃作用,广泛应用于钛合金部件阻燃涂层。本文采用等离子喷涂和火焰喷涂在Ti40钛合金基体材料上制备了NiCrAl+YSZ+NiCrAl/膨润土复合涂层,厚度为2mm,并研究了复合涂层的热喷涂制备过程对钛合金基材组织和基本力学性能的影响。结果表明,NiCrAl/膨润土复合涂层体系对Ti40钛合金基体的组织和力学性能基本无影响,可采用大气等离子喷涂和火焰喷涂制备复合功能涂层的方法对Ti40合金进行防护。     

Morphological and technological characteristics of silicon nitride powder prepared by self-propagating high-temperature synthesis

Silicon nitride produced by self-propagating high-temperature synthesis is ground in planetary and ball mills successively in both devices. The size distribution of particles, specific surface, shape factor, structure, and bulk density are evaluated. The behavior of powder pelletized with synthetic rubber under compaction and sintering in a nitrogen atmosphere in a charge containing magnesium oxide is studied. Powder after ball milling appears to be the most technologically efficient. Empirical equations are obtained which connect bulk density and shrinkage during sintering of powders with their morphological characteristics. The increase in density during compaction governed by the physicomechanical properties of silicon nitride powder and the plastifier is similar for all of the powders tested.Translated from Poroshkovaya Metallurgiya, No. 11(359), pp. 16–21, November, 1992.     

Theoretical consideration on composite oxide scales and coatings

The present paper discussed some fundamental aspects on composite oxide scales and coatings for protection of alloys from high temperature oxidation, the related thermodynamic conditions, special mechanical characteristics and a sealing mechanism. It was proposed that the oxide scales and coatings with a composite structure should possess superior mechanical properties than that with a single phase oxide. It also showed that the Al2O3 scales or coatings doped with Y2O3 and ZrO2 (or YSZ)-Al2O3 composite coatings possessed superior properties at high temperatures. In such composite oxide scales and coatings, the fracture resistance of the scales was increased by the toughening effect, the thermal stress was decreased owing to the increase of thermal-expansion coefficients, and Al2O3 phase could seal the alloy substrate well. In addition, the kinetic equation of thermal growth oxide on alloy covered with composite oxide coatings was derived.     

Formation and properties of laser coatings based on oxynitride ceramic

The structure and properties of powder composite material coatings based on TiN-Al₂O₃ produced by plasma deposition and subsequent laser fusion, have been examined. X-ray spectral microanalysis, electron microscopy and metallographic analysis were used to establish that the coating structure with a high level of physicomechanical properties, is reinforced with Al₂O₃ fibers, and is formed under substrate irradiation conditions that are close to those for sintering and hot compaction.Translated from Poroshkovaya Metallurgiya, No. 12 (360), pp. 29–33, December, 1992.     

Laser treatment of plasma-deposited coatings on powder steel

Results are presented for a study of the structure, phase and chemical composition of plasma coatings deposited on powder steel and treated with a powerful CO₂-laser. Conditions for coating homogenization are analyzed and surface cracking is studied. The effect of the energy contribution on a set of physicomechanical properties and the tribological characteristics of materials is demonstrated.Translated from Poroshkovaya Metallurgiya, No. 10, pp. 25–28, October, 1992.     

Anodic behavior of nitride-coated titanium alloys in the sulfate acid solution

The corrosion behavior of nitride-coated titanium alloys VT1-0, OT-4, and VT-14 in 80% aqueous solution of sulfate acid is studied. The coatings were formed with graphite baking and without it in commercially pure nitrogen under atmospheric pressure and in the rarefied medium (1 Pa) at 750–1000°C for 5–20 h. It was found that the coatings have high protective properties. Anodic behavior of nitride layers depends on a nitride phase ratio in the coating, their stoichiometry, and surface profile and imperfection, which are determined by formation conditions of coatings (temperature, exposure, nitrogen pressure, and other parameters of the technological medium). It is shown that saturation in a two-component medium (molecular nitrogen and graphite cahrging) improves the electrochemical characteristics of nitride coatings not affecting their structural and phase state.     

New self-lubricating antifriction materials based on titanium nitride

Tribological properties of powder composite materials of the skeletal and matrix types are studie under conditions of dry friction with rates up to 10 m/sec in air in pair with steels. Titanium nitride is used in order to obtain skeletons, and the matrix is polytetrafluoroethylene (PTFE). It is established that the tribological properties depend on the type of structure. In level of wear resistance materials of the skeletal type surpass by a factor of 1.5 the original compact materials, and filled PTFE by a factor of eight to nine. Use of PTFE makes it possible to improve markedly the tribological properties of composite materials based on titanium nitride and to reduce significantly (up to 40%) the weight of friction assemblies.     

Physicomechanical properties of the hydrogen-accumulating intermetallics LaNi5 and TiFe and a LaNi5-Al composite

Some physicomechanical properties of the hydrogen-accumulating intermetallics LaNi₅ and TiFe and a LaNi₅-20 wt % Al composite are determined by kinetic microindentation. Indentation diagrams are obtained in the load P-indentation depth h-time t coordinates. The following main dependences and properties of the materials are calculated using these indentation diagrams: the dependence of the hardness on the indentation depth, the influence of the strain rate on the hardness, the activation volume, Young’s modulus, and the hysteresis losses during cyclic loading. The parameters characterizing the resistance of the material to disintegration during cycling under hydrogen sorption-desorption conditions are determined.     

Effect of impurities on the properties of silicon nitride materials

Conclusions The presence of oxides in silicon nitride leads to the formation of an intergranular vitreous phase which has an adverse effect on the high-temperature physicomechanical characteristics of constructional silicon nitride ceramics. This phenomenon is particularly pronounced with silicon nitride contaminated with calcium, silicon, and alkaline metal oxides. Future development work on oxidation-resistant constructional materials based on silicon nitride should go in the directions of removal of impurities and use of additions forming solid solutions or refractory compounds with Si₃N₄ and SiO₂. Additions which can be employed for this purpose include oxides of AI, Mg, Y, and some rare-earth elements.Translated from Poroshkovaya Metallurgiya, No. 1(193), pp. 75–80, January, 1979.     

Fabrication and Characterization of Ni-SiC Nanocomposite Coatings on Al Substrates by Ball Impact Deposition Method

Micron-size Ni and SiC powder mixtures were used to prepare Ni-SiC nanocomposite coatings on an Al substrate by employing a high-energy ball milling technique. Ni:SiC weight ratio was varied over a wide range to explore the effect of the charge composition on the microstructure, composition, microhardness, and wear properties of the depositions. It was observed that the composition of the produced coating was correlated to the charge composition in a complex manner, which suggests that deposition rates for Ni and SiC particles significantly vary depending on the charge composition; SiC deposition rate was higher than that of Ni when Ni:SiC weight ratio was greater than 3:1. Diffusion of Al from the substrate into the Ni matrix provided evidence for the metallurgical bonding at the interface. Both microstructural and mechanical properties of the produced coatings were found to be crucially dependent on the charge composition. By increasing the SiC content in the charge from about 5 to 33 wt pct, the mechanical properties enhanced due to the dispersion strengthening effect of the incorporated SiC particles in the coatings and the crystallite size of the Ni matrix decreasing to the nanometer range. However, a further increase resulted in the formation of a coating with a poor degree of compaction. It was found that the composite coating with about 15 vol pct SiC, produced from the charge with Ni:SiC weight ratio of 2:1, showed a microhardness as high as 830 HV_0.05 along with excellent wear resistance. Despite the current sample size limitations for applying high-energy ball milling, the present findings demonstrate that the adopted technique holds good prospect for the synthesis of nanostructured metal matrix composite coatings with enhanced and tunable properties.

     

Thermomechanical Strengthening of Powder Stainless Steel of the Austenitic Class and Wear-Resistant Composites Based upon It

The effect of thermomechanical strengthening of powder materials of several compositions (steel Kh18N15 without additives, with added carbon, and also with additions of Cr₂C₃, MoS₂ and carbon) during hot forming is established by experiment. This effect is detected by comparing the physicomechanical properties of specimens, prepared by high-temperature thermomechanical treatment, with specimens of a similar composition subjected to complete annealing and hardening after separate heating. The different nature in the dependence of strength properties for steel Kh18N15 without additions and a composite based upon it on shear strain intensity during forming is established. Thermomechanical strengthening of hot-formed single-phase stainless steel is traditional in nature: with an increase in the intensity of shear strain steel strength properties increase, but conversely for a composite they decrease and this is explained by the specific nature of its structure formation during forming.     

Composite electrolytic nickel-phosphorus-boron coatings

Conclusions The feasibility is demonstrated of obtaining Ni-P-B coatings with a uniform distribution of boron particles in their Ni-P matrices. The presence of boron particles has a marked effect on the phosphorus content of such coatings and on the rate of deposition of nickel. Diffusion annealing of Ni-P-B coatings leads to the formation of a new phase and to an improvement in their physicomechanical properties, in particular hardness and wear resistance.Translated from Poroshkovaya Metallurgiya, No. 10(226), pp. 71–74, October, 1981.     

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.     

高温可磨耗复合梯度涂层喷涂工艺研究

按照常压等离子喷涂工艺路线,选择合理的喷涂工艺参数和复合喷涂材料的配比,使用常压等离子喷涂设备在发动机结构件上制备出了高温可磨耗复合梯度封严涂层。对该涂层显微组织、EDS微区成分、涂层组织抗氧化性和涂层氧化增重曲线的测试分析表明,涂层的结构和性能符合相关标准,制备的涂层达到了高温可磨耗封严涂层的使用要求,并已得到实际应...     

Physicomechanical properties of detonation coatings made from stainless-steel powders

A method has been developed for determining the strength and plasticity characteristics of detonation coatings; the structure and phase factors have been used along with the physicomechanical characteristics and the adhesion to optimize the production conditions. Phase transformations occur during the formation of the coatings that govern the strength, ductility, and tribotechnical properties. In spite of the structural and phase changes that accompany coating formation, layers up to 0.25 mm thick have the properties of the compact materials.Institute of Problems of Materials Science, National Academy of Sciences of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 59–66, July–August, 1994.     

Structure and Properties of Composite Electrospark,Laser, and Magnetron Deposited AlN ― TiB2 Coatings

A comparative investigation of the coatings produced by electrospark alloying, laser gas-powder deposition, and magnetron sputtering using composite AlN ― TiB₂ material was carried out. It is shown that the presence of oxygen in the working atmosphere is responsible for the oxidation of aluminum nitride, and also the appearance of refractory compounds of the Ti ― Al ― O system in the coatings. During electrospark and laser alloying globular regions form on the surface by a mechanism of liquid-phase sintering, due to the mass transport of a metallic component from the substrate. The composite layer of a magnetron coating sinters by a mechanism of solid-phase interaction. The dispersion-strengthened structure of electrospark coatings is highly wear resistant, while the continuity, high dispersion, and heterogeneity of the structure of magnetron coatings permits their recommendation for corrosion protection.     

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The tribological properties of materials were studied under conditions which model the collective and individual effects of outer space factors (vacuum, cryogenic temperatures, solar electromagnetic radiation). The behavior of aerospace materials (structural materials, self-lubricating composite materials, antifrictional solid lubricant coatings, wear-resistant coatings, etc.) were investigated. An approach to the design of materials for friction units is proposed, based on the concept that the materials of a friction pair are a complex self-organizing system. This made it possible to substantially expand the range of application of materials and coatings, and aided in the creation of new antifriction materials with pre-determined properties.