Structure and Properties of Ceramics Based on Tungsten and Titanium Borides and Boron Carbide

The W₂B TiB₂ B₄C ceramics studied were hot-pressed from composite powders synthesized by thermal reduction of boron carbide. The resulting materials have a skeleton structure with a boron carbide binder when the B₄C content is high and an inclusion-matrix structure when the B₄C content is low. The grain size varies from 5 to 20 m, depending on the preparation conditions. The composite has a hardness of 17.5-20 GPa with a strength in the range 500-1000 MPa.     

Structure and Properties of Detonation Coatings Based on γ-TiAl

Investigations of a coating ― substrate composite before and after oxidation in air at 900°C revealed that the main structural features were: formation of an Al₂O₃ scale on the surface of the TiAlCrSc(γ) coating (as a result of oxidation) and of inner layer at its interface with a 90% titanium substrate (as a result of diffusion in the composite). The observed phenomenon was caused by a Kirkendall effect resulting in the formation of titanium-enriched phases, apparently Ti₃Al and α-Ti, which have a broad homogeneity range. The formation of a diffusion zone in the system with displacement of the Kirkendall plane in the direction of the substrate has a positive effect on the adherence of the coating. Furthermore, the filling of vacancies and pores in the coating with additional material supplied by the diffusion of titanium should have a favorable effect on the strength and durability of the coating, particularly its fatigue resistance.

     

氧化锆基金属陶瓷放电等离子烧结制备与性能研究

氧化锆陶瓷材料的脆性限制了其在某些领域的应用。文章首创在氧化锆粉末中加入316L不锈钢粉,通过放电等离子烧结制备氧化锆基金属陶瓷。试验通过不同的成分配比和不同的烧结温度进行对比研究,采用金相分析、XRD、SEM/EDS等测试方法,对材料的微观结构和宏观性能等进行了表征与分析。并通过断口分析,讨论了Zr O2·316L金属陶瓷的增韧机理。结果表明:采用放电等离子烧结制备出的材料随相组成的成分所占比例的改变,其致密度、弯曲强度、横向断裂强度、断裂韧性都随之呈现出相应的变化规律;316L相以片状均匀分布在氧化锆基体中,在材料断裂时起到了颗粒/纤维增韧的作用。同时氧化锆部分以亚稳相t-Zr O2的形态存在,也起到了相变增韧的作用。     

Structure and Properties of Ferrites Based on CuFe2O4

We have studied the magnetic and structural properties of the solid solutions M _x ²⁺ Cu _1?x ²⁺ Fe ₂ ³⁺ O₄, where M = Mg, Ni, Co, Zn, Mn, Me _0.5x ⁺ Cu _1?x ²⁺ Fe _2+0.5x ³⁺ O₄, were Me = Li, Cu, and (Mn₃O₄)_x(CuFe₂O₄)_1?x. We have developed a new method for detecting a tetragonal phase and have used this method to determine the range of existence for solutions with a tetragonal structure. We explain the dependence of these ranges on the nature of M and Me.     

Structure and Properties of Wear-Resistant Detonation Coatings Based on Titanium Carbonitride

An investigation was made of the composition, structure and wear rate of detonation coatings on steel 30KhGSNA deposited from composite powders based on TiC_0.5N_0.5 with refractory additions of SiC, AlN, and a Ni – Cr metallic binder. It was shown that at a load of 10 MPa coatings based on titanium carbonitride exhibit substantially less wear and a larger range of sliding velocities with a stable value of wear than coatings of the hard alloy VK15 (WC – 15% Co). The physico-chemical reactions in the process of tribo-oxidation were analyzed.     

Studies on the Properties of PT-MN Ceramics

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O''''-Sialon基陶瓷的性能及应用

系统地评述了目前研究较多的O－Sialon基陶瓷如O－Sialon基陶瓷O′－β′-Sialon、O′－Sialon-ZrO2、O′－Sialon-TiN等的机械性能、热物理性能和化学稳定性，介绍了展望了O′－Sialon基陶瓷的具体应用及发展前景。     

Effect of Lithium Carbonate on the Structure Formation of Ceramics Based on Si3N4

Structure formation in the system Li₂CO₃ Si₃N₄ both during heating in the powder state (500-1450°C) and also during specimen sintering (1450-1750°C) is studied. The most active formation of binary Li Si nitrides (LiSi₂N₃, Li₂SiN₄, Li₈SiN₄) is observed at 1450-1550°C. With a controlled sintering temperature and the amount of added Li₂CO₃ it is possible to prepare materials based on silicon nitride with a prescribed phase composition and corresponding properties.     

熔石英基复合材料性能的研究

用热压烧结方法制得碳纤维与氮化硅颗粒复合补强增韧熔石英基复合材料,其熔石英基体保持非晶态,只有少量鳞石英析出。材料的抗弯强度达到１１３．７ＭＰａ,断裂韧性为１．５３ＭＰａ．ｍ＾１／２,补强增韧效果明显。     

BaTi0.9Zr0.1O3:xTb4O7介电陶瓷的研制及其结构与介电特性的研究

采用溶胶．凝胶法制备了一系列的BaTiO3：xTb4O7,BaTi0.09Zr0.1O3;：xTb4O7粉体。测试表明所获得陶瓷在室温具有高介电常数。通过XRD衍射和SEM扫描电镜分别对粉体的结构和陶瓷的形貌进行了表征。此外，采用溶胶．凝胶法合成BaTi0．09Zr0.1O3后，再用固相法掺杂了Tb4O7介-温测试表明固相掺杂Tb4O7使陶瓷的居里温度向低温方向移动，陶瓷的室温介电常数显著提高。     

Study on Synthesis,Structure and Properties of Ba0.9 Sr0.1 TiO3: x Eu2 O3 Ceramics

A series of BaTiO₃ solid solutions were synthesized by sol-gel method during different aging time. The effect of aging time on the dielectric properties of BaTiO₃ ceramics was discussed. A series of BaTiO₃: x Eu₂O₃ and Ba_0.9Sr_0.1TiO₃: xEu₂O₃ solid solutions were synthesized by sol-gel method and their properties were investigated. The ceramics obtained were of high dielectric constants at room temperature. The results indicated that the dielectric properties of BaTiO₃ ceramics were improved by doping with Eu₂O₃. The doping of Sr²⁺ resulted in the decrease in T_c and the increase of dielectric constant. The dopant Eu³⁺ not only caused the decrease in T_c, but also caused the broadening of Curie peak.     

Studies and Properties of Ceramics with High Thermal Conductivity

The sintering technology of the AlN ceramics power were discussed. It is discussed that the compound sintering aids is consistent with the enhancement of the the thermal conductivity of AlN ceramics, and sintering technics is helped to the improvement of density. It is analyzed how to sinter machinable AlN ceramics with high thermal conductivity. And the microstructure of compound ceramics based on AlN was studied.     

单相Sm掺杂BaTiO3陶瓷的结构研究

采用高温固相反应法,在1 400℃/12h烧结条件下制备了具有Ti空位补偿的Ba1-xSmxTi1-x/4O3(BST;x=0.02~0.07)陶瓷。利用XRD对BST陶瓷的晶体结构进行表征,并在532和638nm两种激发波长下对其进行拉曼光谱测试。结果表明:当x≤0.07时,所有的BST陶瓷均表现为单相钙钛矿结构,并且随着Sm含量的增加,其晶体结构由四方相(x≤0.06)转变为立方相(x=0.07);不同激发波长下的拉曼测试证实高频谱来自稀土Sm^3+的荧光效应。     

Effect of LiF on Densification and Mechanical Properties of Dy-α-Sialon Ceramics

The effect of LiF on the densification and mechanical properties of hot-pressed Dy-α-sialon ceramics was studied. Comparatively, without LiF as sintering additive, the pure Dy-α-sialon ceramic should be sintered at 1750 ℃. When LiF is used, the sintering temperature of the Dy-α-sialon is greatly lowered to 1500～1650 ℃. Obviously, the addition of LiF has a strong effect on the improvement in densification. Meanwhile, the resultant Dy-α-sialon has no significant changes in the mechanical properties.     

Structure and Properties of High-Temperature Multilayer Hybrid Material Based on Vanadium Alloy and Stainless Steel

The present work is devoted to the development of new structural composite material having the unique complex of properties for operating in ultrahard conditions that combine high temperatures, radiation, and aggressive environments. A new three-layer composite tube material based on vanadium alloy (V-4Ti-4Cr) protected by stainless steel (Fe-0.2C-13Cr) has been obtained by co-extrusion. Mechanism and kinetics of formation as well as structure, composition, and mechanical properties of “transition” area between vanadium alloy and stainless steel have been studied. The transition area (13- to 22-µm thick) of the diffusion interaction between vanadium alloy and steel was formed after co-extrusion. The microstructure in the transition area was rather complicated comprising different grain sizes in components, but having no defects or brittle phases. Tensile strength of the composite was an average 493 ± 22 MPa, and the elongation was 26 ± 3 pct. Annealing at 1073 K (800 °C) increased the thickness of transition area up to 1.2 times, homogenized microstructure, and slightly changed mechanical properties. Annealing at 1273 K (1000 °C) further increased the thickness of transition area and also lead to intensive grain growth in steel and sometimes to separation between composite components during tensile tests. Annealing at 1073 K (800 °C) is proposed as appropriate heat treatment after co-extrusion of composite providing balance between diffusion interaction thickness and microstructure and monolithic-like behavior of composite during tensile tests.

     

Influence of Rare Earths on Electric Properties and Microstructure of Barium Titanate Ceramics

The influence of rare earths on electrical resistivity and microstructure of barium titanate ceramics doped with rare earth ions Y, Dy, Ho, Er and Y at the concentrations of x = 0.001 × 0.01 was investigated by the means of X-ray diffraction, scanning electron microscopy and electric properties testing. The results showed that a dramatic decrease in resistivity occurred at the concentration of 0.3% of La-doped sample. However, the range of concentration for semiconducting samples doped with Dy, Ho, Er and Y was wider, especially for Y-doping. The experimental results indicated that below the critical concentration of Dy, Ho, Er and Y, the substitution took place in the barium sublattice with electronic compensation, above the critical concentration, gradually the rare earth ions began to substitute for titanium. As for Hodoped BaTiO₃ ceramic, the resistivity jump (PTCR effect) near the Curie temperature was the highest in case of lower dopant concentration of 0.3%. Fine-grained structure of sample doped with 0.6% Dy led to the increasing of breakdown electric field strength and dielectric constant of ceramic samples. In contrast, coarsed-grained structure of sample doped with 0.3% Dy showed semiconducting property.     

Influence of Manganese Oxide and Silica on the Morphological Structure of Hematite Compacts

Dry compacts of pure Fe₂O₃ and Fe₂O₃ doped with either (2–6 mass%) MnO₂, (2.5–7.5 mass%) SiO₂ or with both (2–6% MnO₂ + 7.5% SiO₂) were indurated at 1373 K for 6 hours and physically and chemically characterized. The fired compacts were isothermally reduced with pure CO gas at 1073–1373 K. The O₂‐weight loss was continuously recorded as a function of time using TGA technique. The external volume of pure and doped compacts was measured at different reduction conditions and the volume change was calculated. The structural changes accompanying the reduction process were visually and microscopically examined and the different phases were identified by X‐ray diffraction analysis. After firing, manganese ferrite (MnFe₂O₄) phase was identified in MnO₂‐doped compacts. In pure Fe₂O₃ compacts, the external volume of compacts was increased with reduction temperature, showing a maximum swelling value at 1198 K. Catastrophic swelling was observed in MnO₂‐doped Fe₂O₃ compacts, the volume change increased with MnO₂ content showing catastrophic swelling in compacts containing 6%MnO₂ at 1248 K. The catastrophic swelling was attributed to the formation of dense metallic iron whiskers and plates in a highly porous structure. Unlike in MnO₂‐doped samples, no considerable volume changes were detected in SiO₂‐doped Fe₂O₃ and (MnO₂ + SiO₂)‐doped Fe₂O₃ compacts where the presence of silica greatly hindered the swelling phenomenon at all reduction temperatures.     

Preparation, Structure and Mechanical Properties of Nickel Based Porous Spherical Superalioy

The porous superalloy materials with hollow spherical pores were fabricated by using metal powder sintering process. The scanning electron microscope (SEM) observation was applied to the test samples and it revealed that the pores of the porous material exhibited a uniform distribution and the apertures were of same size in principle. The sintering necks appeared between adjacent particles on metal skeleton after sintering. The mechanical properties of the test samples were analyzed and the result showed that this kind of materials possessed excellent energy absorption capability, and the compression resistance decreased with increasing the porosity and aperture.