Influence of Aluminum Additives on the Content and Parameters of the Fine Structure of Titanium Silicon Carbide in SHS Powders

The dependence of the phase composition and parameters of a fine structure of titanium silicon carbide in powders formed by the self-propagating high-temperature synthesis on the aluminum concentration in the 5Ti/2Si/1C reaction mixture is investigated. The aluminum content is varied in a range of 0.1–0.4 mole fraction with the conservation of the total carbon content. It is established that the additives of aluminum not only affect the yield of titanium silicon carbide, but also promote the preferential formation of Ti5Si3 in synthesis products instead of TiSi2 identified in powders containing no aluminum. The introduction of a small amount of aluminum (0.1 mole fraction) leads to the formation of the Ti3Si1 – xAlxC2 solid solution and makes it possible to decrease the content of impurity phases in SHS powders by 6%. The silicon carbide concentration in SHS powders decrease at a higher aluminum content in the reaction mixture, while that of binary compounds (TiC, Ti5Si3, TiAl) correspondingly increases. No noticeable effect from the introduction of aluminum on the parameters of the crystal lattice of titanium silicon carbide in SHS powders is found in concentration limits of 0.1–0.25 mol %. A noticeable increase in parameters of a and c for Ti3Si1 – xAlxC2 (from a = 3.067 Å, c = 17.67 Å to a = 3.07 Å, c = 17.73 Å) with the conservation of the c/a ratio in limits of known values (c/a = 5.78) is observed only with the aluminum concentration of 0.4 mole fraction. The crystallite size of titanium silicon carbide depends, first and foremost, on the combustion parameters. At the same time, the deformation of the crystal lattice of Ti3Si1 – xAlxC2 in SHS powders increases monotonically with an increase in the aluminum content in the reaction mixture in the concentration range under study.     

无莱氏体超硬高韧高速钢M2Si

与Ｍ２钢对比，新型高速钢Ｍ２Ｓｉ的硅含量提高到１．０％，碳含量降至０．５５％。该钢渗碳、淬、回火后的表面硬度高于６７￣６８ＨＲＣ，心部硬度为５５ＨＲＣ，无碳化物偏析及粗大碳化物，是一种价廉的超硬高韧高速钢。     

碳、硅铁及碳化硅对白钨矿还原动力学的影响

在实验室用15 kW碳管炉进行碳粉、硅铁粉(75％Si)、碳化硅粉对白钨矿粉(67．25％WO3)还原动力学影响的研究。结果表明,碳还原白钨矿的反应级数为二级,反应表观活化能为234．6 kJ／mol;碳在较低温度下,反应性能差,当温度达到1 400℃时,反应剧烈;随温度升高,硅铁的还原性能比较平稳,反应产生SiO₂,使渣量增加;碳化硅高温反应性能好(≥1 400℃);碳和硅铁适合较低合金化率(3％W),碳化硅适宜用于较高的合金化率(≥5％W)。     

Si对Ti3SiC2/Al复合材料的摩擦性能影响

MAX相因其独特的晶体结构和优良的自润滑性能受到广泛的关注,作为新型固体润滑剂添加到金属基复合材料可获得良好的摩擦磨损性能.采用铝粉、硅粉、Ti₃SiC₂粉为原材料,通过冷压成型无压烧结法制备了Ti₃SiC₂增强铝硅基复合材料.研究发现,复合材料的组成物相除Al、Si及外加Ti₃SiC₂相之外,在烧结的过程中生成了Al₂O₃和Al₄C₃随着硅元素含量质量分数的增加,大的圆球形Ti₃SiC₂逐渐减小,摩擦系数和磨损失重均呈现先减小后增大的规律.当硅的含量为12.5 %时,摩擦系数最低,其值为0.18,磨损失重也达最低;随着硅含量的增加,材料的硬度先增大后趋于平缓,致密度呈线性下降趋势.通过磨损表面SEM分析初步揭示了金属基自润滑的机理,复合材料的磨损机制为磨粒磨损、剥层磨损和氧化磨损并存.      

红外吸收法测定铝碳化硅碳砖中碳化硅量

根据铝碳化硅碳砖的组成特点，对各种常用炭素材料和碳化硅的分解温度进行试验，找出了各种常用炭素材料与碳化硅的分解温度的不同，并据此通过高温灼烧法将炭素材料中各种形式的碳与碳化硅中碳分离。应用HCS－140型红外碳硫分析仪，对碳化硅中碳的测定条件进行了研究，在选定的工作条件下，用红外吸收法测定碳化硅中碳的含量，从而换算出碳化硅量，取得了满意的结果。     

反应烧结碳化硅陶瓷内筒的损毁机制

以X射线衍射仪、扫描隧道电子显微镜、能量散射光谱仪等手段对在悬浮预热器内筒上使用前后的反应烧结碳化硅陶瓷进行分析,研究该陶瓷应用于悬浮预热器上的损毁机制.碳化硅陶瓷中残存金属硅和表面的碳化硅在高温使用工况下首先氧化成SiO₂,SiO₂在K₂O (g)、Na₂O (g)、KCl (g)、Na Cl (g)等蒸气以及氯化物作用下黏度降低,形成覆盖于陶瓷表面的氧化层,继而被高速的气固流体冲蚀和磨损掉,并导致新的界面出现.如此循环,使碳化硅陶瓷的外侧逐渐变薄和断裂,直至损毁.提高陶瓷的致密性和降低残余硅含量是改进反应烧结碳化硅陶瓷在悬浮预热器中使用性能的有效途径.      

粉末压片-X射线荧光光谱法测定含碳化硅铝质耐火材料中8种组分

含碳化硅耐火材料已广泛地应用于冶金炉料中,目前对含碳化硅耐火材料测定常采用湿法分析,然而这些方法繁琐耗时,不适合大批量检测要求。实验采用聚酯(PET)薄膜包裹粉末压片法制样,以微晶纤维素为粘结剂,选取与待测试样粒度一致、基体相似、各成分含量有梯度的铝硅系耐火材料标准样品和碳化硅标准样品,按照不同的比例,配制成各组分含量从低到高具有一定梯度含碳化硅铝质耐火材料校准样品,对其拟合校准曲线,建立了X射线荧光光谱法(XRF)同时测定含碳化硅铝质耐火材料中TSi、Fe₂O₃、Al₂O₃、CaO、MgO、TiO₂、P₂O₅、K₂O含量的快速分析方法。采用PET薄膜包裹压片不仅减少粉尘污染,把对仪器损坏的几率降到了最低,而且可以防止压片暴露在空气中,增加压片保存时间。对含碳化硅铝质耐火材料试样进行了精密度考察,各组分测定结果的相对标准偏差(RSD,n=10)为0.08%～3.7%。采用实验方法对合成含碳化硅铝质耐火材料校准样品(未用于校准曲线绘制)和实际样品进行测定,结果与参考值或国标方法的分析值相吻合。     

Feasibility of Electrochemical Deposition of Nickel/Silicon Carbide Fibers Composites over Nickel Superalloys

Nickel superalloys are typical materials used for the hot parts of engines in aircraft and space vehicles. They are very important in this field as they offer high-temperature mechanical strength together with a good resistance to oxidation and corrosion. Due to high-temperature buckling phenomena, reinforcement of the nickel superalloy might be needed to increase stiffness. For this reason, it was thought to investigate the possibility of producing composite materials that might improve properties of the metal at high temperature. The composite material was produced by using electrochemical deposition method in which a composite with nickel matrix and long silicon carbide fibers was deposited over the nickel superalloy. The substrate was Inconel 718, and monofilament continuous silicon carbide fibers were chosen as reinforcement. Chemical compatibility was studied between Inconel 718 and the reinforcing fibers, with fibers both in an uncoated condition, and coated with carbon or carbon/titanium diboride. Both theoretical calculations and experiments were conducted, which suggested the use of a carbon coating over the fibers and a buffer layer of nickel to avoid unwanted reactions between the substrate and silicon carbide. Deposition was then performed, and this demonstrated the practical feasibility of the process. Yield strength was measured to detect the onset of interface debonding between the substrate and the composite layer.

     

SiC复相陶瓷的强化增韧趋势

SiC陶瓷因其具有优良的性能而广泛应用于军事和民用领域.但陶瓷固有的脆性严重影响了其作为结构材料的应用潜力,因此sic陶瓷的强化增韧成为了近年来研究的热点.综述了siC基复相陶瓷的几种主要强化增韧方式,讨论了其强化增韧机制.采用纳米颗粒、晶须协同强化增韧和特殊技术制备纳米复相陶瓷将是提高SiC基陶瓷性能的有效途径.     

助剂用量对反应烧结碳化硅结构及力学性能的影响

以碳化硅、碳黑和石墨为原料, 聚乙烯吡咯烷酮K90、K30为分散剂, 聚甲基丙烯酸铵CE-64为减水剂, 采用注浆成型工艺制备碳化硅素坯, 并在1700℃下对素坯进行反应烧结制备碳化硅成品, 研究了分散剂、减水剂用量对浆料黏度、素坯密度、素坯孔隙率和成品微观组织及力学性能的影响。结果表明: 随着助剂用量的增加, 浆料黏度总体上呈现下降趋势, 素坯密度呈先降后升趋势, 素坯孔隙率呈先升后降趋势。当K90、K30、CE-64的质量分数分别为3.8%、2.0‰、4.3‰时, 所得素坯的孔隙分布均匀, 素坯中碳化硅分布较为疏松, 渗硅通道较多, 有利于碳和硅粉的充分反应, 获得的烧结制品性能优良。     

Role of bulk and mass effects of reactions in reaction sintering processes

Peculiarities of the fabrication of ceramic porous and dense composite materials based on compounds of the Si–C–O–N system with the participation of chemical reactions and the formation of new phases are discussed. An analysis of comparatively new technologies is attempted in terms developed in earlier studies on the reaction sintering of silicon nitride, carbide, and oxynitride. It is shown that the approach to reaction sintering that includes the selection of promising reaction systems allowing for the bulk effect of reactions accompanying material formation can be extended to the fabrication of porous and highly porous materials. In contrast to the fabrication of dense materials, when reaction systems with positive bulk effects are used, the reaction systems with negative bulk effects can be used in the fabrication of highly porous materials.     

Wetting Properties of Molten Silicon with Graphite Materials

The wetting behavior of refractory materials by molten silicon is important in the refining and casting of silicon with respect to production of low-cost solar cells. Here we studied the wetting properties of several graphite materials by molten silicon. These materials are used in the photovoltaic industry. The sessile drop method is employed to measure the contact angles. Initially, molten silicon does not wet graphite materials. The initial contact angles measured are approximately 120 deg. Molten silicon will react with C to form β-SiC and to infiltrate the refractory. Because losses of Si should be minimized, infiltration of Si into the refractory also is a problem. Surface roughness increases the contact area between Si and refractory and thus the loss of Si. Equilibrium wetting angles of 0 deg to 31 deg are measured. With increasing surface roughness, the equilibrium wetting angles decrease. The results show that the infiltration depth of molten silicon increases with the average pore size of graphite materials.     

硅/碳复合材料的高温热解法制备及其电化学性能

采用高温热解方法成功地合成了高容量硅/碳复合负极材料.通过X射线衍射分析、热重分析、扫描电子显微镜观察、透射电子显微镜观察、恒电流充放电测试、循环伏安法等手段研究了复合材料的性能.结果表明:硅/碳复合材料由Si、C以及少量SiO₂组成;硅/碳复合材料中碳的质量分数约在39%左右;经电化学性能测试,在电流0.2 m A下,该硅/碳复合材料首次充电容量768 m Ah·g-1,首次库仑效率75.6%,70次循环后可逆比容量仍为529 m Ah·g-1,平均容量衰减率为0.44%.这些性能改善归因于硅/碳复合材料中碳的引进,硅表面存在的碳涂层提供了一个快速锂运输通道,降低了电池的阻抗并且充放电过程中稳定了电极的组成.      

Effects of rare earth on microstructures and properties of Ni-W-P-CeO2-SiO2 nano-composite coatings

Ni-W-P-CeO2-SiO2 nano-composite coatings were prepared on common carbon steel surface by pulse electrodeposition of nickel, tungsten, phosphorus, rare earth (nano-CeO2) and silicon carbide (nano-SiO2) particles. The effects of nano-CeO2 concentrations in electrolyte on microstructures and properties of nano-composite coatings were studied. The samples were characterized with chemical compositions, elements distributions, microhardness and microstructures. The results indicated that when nano-CeO2 concentration was controlled at 10 g/L, the nano-composite coatings possessed higher microhardness and compact microstructures with clear outline of spherical matrix metal crystallites, fine crystallite sizes and uniform distribution of elements W, P, Ce and Si within the Ni-W-P matrix metal. Increasing the nano-CeO2 particles concentrations from 4 to 10 g/L led to refinement in grain structure and improvement of microstructures, while when increased to 14 g/L, the crystallite sizes began to increase again and there were a lot of small boss with nodulation shape appearing on the nano-composite coatings surface.     

Solid state reactions between silicon carbide and (Fe,Ni, Cr)-alloys: reaction paths,kinetics and morphology

Solid state reactions between silicon carbide and various (Fe, Cr, Ni)-alloy compositions are studied. The different phases present in the reaction scale, their chemical composition and morphology are determined. The reaction path and the reaction kinetics are also measured. A typical composition distribution and morphology of the reaction scale is associated to each alloy element: iron yields broad α-iron zones with randomly distributed graphite precipitates; the presence of nickel results in typical reaction scales made of alternating bands of pure silicide and other bands of silicide containing a high density of carbon precipitates; chromium leads to large chromium carbide precipitates on the alloy side. The solid state reactions between SiC and (Fe, Cr, Ni)-alloys can be described as the dissolution of silicon carbide by iron and nickel, resulting in the formation of silicon-rich compounds (α-, τ-phase, Ni₅Si₂ or Ni₂Si) and in the precipitation of graphite flakes.     

原料对硅氧化物纳米球形成的影响

以硅、二氧化硅为硅源探讨了水热沉积条件下原料对硅氧化物纳米球形成的影响。实验表明,硅、二氧化硅的混合物在水热沉积硅氧化物纳米球时效果最好,所得纳米球直径小、分布较均匀;仅以硅为原料时所得球状结构尺寸大,直径分布范围宽;仅以二氧化硅为原料时则得不到球状结构。二氧化硅对于硅氧化物纳米球的形成起到了重要作用。     

Application of secondary ion mass spectrometry to the study of carburization of superalloy

Secondary ion analysis was applied to the study of the carburization behavior of a superalloy by using the ion microprobe mass analyzer (IMMA). The corrosion test of Inconel 617 was carried out for 1000 h under an environment of methane-doped impure helium gas at 1000 °C. 20 KeV O ₂ ⁺ and N ₂ ⁺ were used as primary ions. IMMA showed that C, O, Al, Si, Ti and Mo were enriched near the surface. The chemical states of the scale and the precipitates were determined from chemical shifts of X-ray emission spectra. It was confirmed that silicon carbide and molybdenum carbide were coprecipitated in the same areas: in the scale, in the matrix at a depth of 10 μm to about 40 μm below the scale, and at grain boundaries. Aluminum and titanium were found to exist as oxides near the surface. It was shown that carburization was limited near the surface, and the grain boundary precipitation of carbides in the bulk was due to aging at high temperatures. The concentration profiles of silicon and molybdenum in (Si,Mo)-carbide were obtained by using standard carbide samples assuming that the concentration of implanted oxygen atoms of the specimen was equal to that of the standard sample. The ratio, (Si)/(Mo), was increased from about 0.1 in bulk to 2.4 ∼ 3.8 near the surface. This result indicates that silicon is carburized much more preferentially than molybdenum.     

Friction Surfaces and Wear Products of Sn–Sb–Cu-Based Composite Materials

The structure and the tribological properties of the composite materials based on an Sn–Sb–Cu alloy (B83 babbit) and fabricated by hot pressing of powders are studied under dry sliding friction conditions. Modified schungite and silicon carbide are chosen as reinforcing materials. The composite material fabricated by a powder technology and reinforced by silicon carbide and modified schungite particles is found to have the doubled wear resistance as compared to a cast B83 alloy at a comparable friction coefficient.     

原位自生Mg_2Si/A1-Si复合材料的稀土与锶盐变质研究

研究了稀土与锶盐复合变质及热处理对原位自生Mg2Si/Al-Si复合材料微观组织的影响。结果表明:随冷却速度的加大,SrCl2与RE复合变质剂对Mg2Si/Al-Si凝固组织中初生α-A1与共晶Si相的变质作用均加强,初生α-A1晶粒生成量增多同时形貌发生趋向球状的转变,共晶Si相形貌则发生板片状向短棒状的转变;在冷却速度较低的砂型铸造条件下,Mg2Si/Al-Si材料凝固组织中,三元共晶Si相受变质剂作用不明显,依然呈板片状生长,此时其可作为三元共晶Mg2Si相的异质形核基底,共晶Mg2Si便依附其上生长;热处理可使Mg2Si/Al-Si铸态组织中共晶硅相转变成细小的颗粒状,断网状的共晶Mg2Si转变成细小的棒状甚至颗粒状,优化了材料组织。     

熔盐电解SiO2/TiO2制备硅钛合金的研究

采用熔盐电解法通过直接电解SiO2、TiO2混合物料来制备硅钛合金。热力学计算结果表明,在700℃下,SiO2和TiO2的理论分解电压分别为1.28V和1.37V,生成的单质硅和钛在高温下能够自发进行合金化反应,生成硅钛系列合金,且容易倾向于生成稳定合金相TiSi2合金。研究表明,以摩尔比50∶1的SiO2/TiO2混合物料为原料,在等摩尔比的CaCl2-NaCl混合熔盐中,在700℃、2.4V槽电压下,经过5h电解后,制备得到TiSi2/Si合金,微观形貌为粒径0.2~2.5μm的多孔颗粒堆积,单质硅颗粒覆盖在TiSi2合金颗粒表面。