Fabrication and High Temperature Strength of Nb3Al by a Modified Reactive Sintering Process

Single phase Nb₃Al alloys and two phase Nb₃Al alloys containing a Nb solid solution (Nb_ss) or Nb₂Al are fabricated by a modified reactive sintering process. This process, called the clad chip extrusion (CCE) method, consists of clad-rolling Al/Nb/Al three layered plates, cutting the clad-rolled plates into pieces, extruding a container filled with the pieces and heat-treating the extruded Nb/Al composite rod with a very fine micro structure. Heat-treatments combined with HIPing are used to form high-density Nb₃Al compacts containing neither Kirkendall voids nor alumina particles. Nb₃Al alloys are brittle below 1300  K and fracture before yielding in compression tests in this temperature region. Single phase Nb₃Al alloys with the compositions from 20·2 to 23·3 at% Al possess very high yield strength in compression above 1473  K. The compressive strengths are almost independent of Al content, and the materials exhibit dynamic recrystallization around initial grain boundaries at large strains. Two phase alloys of Nb₃Al and Nb_ss deform, without cracking at lower temperatures, to larger strains, although they have lower yield strengths.     

Nb5+掺杂对低氟MOD法制备的YBCO薄膜性能的影响

本研究通过低氟MOD法成功地制备了Nb⁵⁺掺杂的YBa₂Cu₃O_7-x(YBCO)薄膜, Nb⁵⁺在薄膜中生成了大小在20~30 nm之间的纳米颗粒; 纳米颗粒的生成不会对 YBCO薄膜的织构和临界温度(T_c)构成明显的影响。由于纳米颗粒的引入, 掺杂后薄膜的临界电流密度(J_c)在整个磁场范围内都要高于纯的YBCO, 自场下的Jc更是达到了3.4 MA/cm²。掺杂薄膜的钉扎力(F_p)也远远大于纯YBCO, 最大钉扎力达到了3.25 GN/m³, 有效地提高了YBCO在外加磁下的超导性能。     

Processing of BSCCO 2212 and 2223 Superconductor Compounds

High-T_c BSCCO superconductor tapes were prepared by the conventional powder-in-tube method. Some tapes involved partial melting, while the others involved solid-state processing only. Bulk samples were prepared by powder metallurgy. X-ray diffraction (XRD) showed the presence of both BSCCO 2223 (T_c = 105 K) and BSCCO 2212 (T_c = 80 K) phases in all the materials. For the mostly BSCCO 2212 phase samples, x-ray studies indicated that tape #1 which involved partial melting at 850^°C for 0.3 h had a higher degree of basal orientation than either a tape #2 sample which involved partial melting at 855^°C for 0.5 h, or a bulk (#2) sample. For the mostly BSCCO 2223 phase samples, however, a comparison of bulk (#1.), tape #3 (solid state processing at 840^°C) and tape #4 (partial melting at 865^°C for 0.5 h) samples, showed that the solid-state processed tape (#3) had the highest degree of basal orientation. Direct current magnetic susceptibility measurements were used to follow the transition at T_c. Critical current density, J_c, values were estimated from DC magnetic hysteresis loops for all bulk and tape samples.     

Processing and Characterization of Fiber Reinforced Intermetallic Matrix Composites

A series of intermetallic matrix composites reinforced with Al₂O₃ based fibers were fabricated by pressure casting. The Al₂O₃ based fibers used were DuPont's 20 μm diameter Fiber FP and PRD-166 fiber, Mitsui's 10 μm diameter Almax fiber, and Saphikon's 125 μm diameter single crystal Al₂O₃ fiber. The intermetallic matrices employed were alloys based on Ni₃Al, NiAl, Fe₃Al, Ti₃Al+TiAl, and Nb₂Al+NbAl₃. Optical, scanning and transmission electron microscopy were used to investigate the microstructure of the composites and the fibers. Tensile testing was conducted to determine the Weibull mean strength of the fibers in the as-received and heat treated conditions. The effect of fiber gage length on the Weibull mean strength of the PRD-166 and Fiber FP was evaluated. Indentation tests were performed to determine the effect of alloying additions on the fiber/matrix bond strength in shear in Saphikon fiber reinforced Ni₃Al composites.     

真空感应熔炼Nb-16Si-22Ti-2Hf-2Cr-2Al合金经高温热处理后的组织和性能

用真空非自耗电弧熔炼法制备了Nb-16Si-22Ti-2Hf-2Cr-2Al母合金锭, 用Y₂O₃坩埚真空感应熔炼对母合金锭重熔, 浇注在温度梯度约为4 ℃/mm的模壳里, 制备出Φ 60 mm×170 mm铸锭, 研究了1500 ℃/100 h真空热处理后铸锭的组织特征对室温抗拉强度和高温压缩性能的影响。结果表明, 真空感应熔炼Nb-16Si-22Ti-2Hf-2Cr-2Al合金经过1500 ℃/100 h热处理后, 合金锭的组成相为Nb_SS枝晶, Nb₅Si₃层片或不规则颗粒和残留Nb₃Si块。块状Nb₃Si的尺寸越大, 发生完全共析转变需要的时间越长、温度越高。热处理合金锭的室温抗拉强度在208~355 MPa之间, 室温延伸率变化不大, 均小于0.3%。残留的粗大块状Nb₃Si和热处理过程中析出的HfO₂是导致合金锭拉伸性能较低的重要原因。合金锭的高温压缩强度受到组织中硅化物相含量的影响, 压缩强度与硅化物含量成正比。      

硅藻土原位生长Nb2O5纳米棒及表面Cr(VI)吸附转化行为研究

以活化铌酸为铌源, 草酸铵为沉积剂, 十二烷基苯磺酸钠为模板剂, 采用水热法在硅藻土表面原位生长Nb₂O₅纳米棒。采用SEM、TEM、XRD、BET、FT-IR和XPS等分析方法对样品进行表征, 反应14 h后, Nb₂O₅纳米棒长度为500~700 nm, 直径为25~35 nm; 硅藻土原位生长Nb₂O₅纳米棒样品比表面积为157 m²/g。研究了样品对Cr(VI)的吸附与光还原行为, 可见光条件下对Cr(VI)吸附量可达220 mg/g; 紫外光条件下, 可将表面吸附的Cr(VI)转变为Cr(III), 样品经过5次循环使用后, 对Cr(VI)(100 mg/L)降解率仍能保持在93%左右。样品可对重金属污染废水中Cr(VI)进行吸附与毒性降解一体化去除。     

过量Nb2O5对偏铌酸铅压电陶瓷烧结性能和电学性能的影响

采用传统的固相烧结法制备了组成为PbNb₂O₆-xmol%Nb₂O₅(x=0, 5, 10, 15, 20)的压电陶瓷样品, 研究了过量Nb₂O₅对PbNb₂O₆压电陶瓷烧结性能和电学性能的影响。研究结果表明, 过量Nb₂O₅能够在保证PbNb₂O₆高居里温度和明显各向异性的条件下改善其烧结性能和电学性能。这可能是因为过量Nb₂O₅导致PbNb₂O₆中Nb-O八面体的扭曲, 进而抑制PbNb₂O₆在烧结过程中的三方到四方相变。随着过量Nb₂O₅加入到PbNb₂O₆中, 其压电系数(d₃₃)和致密度都明显提高了, 并且在过量5mol% Nb₂O₅时达到最大值, 分别为69 pC/N和93.1%。     

溶胶-凝胶法制备Al3+、Yb3+掺杂石英光纤纤芯的研究

以正硅酸乙酯、氯化铝和氯化镱为前驱体, 用溶胶-凝胶法制备了Al³⁺、Yb³⁺掺杂石英光纤纤芯。采用ICP-AES分析发现: 碱催化的掺杂硅凝胶上下层组分存在较大差异, 酸催化条件能够消除组分差异。将酸催化溶胶经凝胶化、热处理、玻璃化、光学加工, 获得了φ2.5 mm×50 mm的芯棒。测试2 mm厚芯棒玻璃的光谱和荧光寿命, 1020 nm的荧光寿命为896 μs, 羟基含量为0.4×10^-6, 并通过显微拉曼光谱分析玻璃结构。采用管棒法制备预制棒, 2000℃高温拉制了Al³⁺、Yb³⁺掺杂单包层石英光纤。用光纤折射率分布测试仪测得纤芯折射率波动Δn小于2×10^-4, 表明纤芯具有良好的光学均匀性。本研究结果提供了一种大模场掺镱石英光纤纤芯材料的制备方法, 并为溶胶-凝胶法制备均匀多组分材料的研究提供了理论参考。     

FABRICATION OF A Ni3Al/Al2O3UNIDIRECTIONAL COMPOSITE BY PRESSURE CASTING

A gas pressure liquid metal infiltration technique for producing fiber reinforced Ni₃Al/Al₂O₃ and Ni₃Al/Al₂O₃ composites has been described. Composite bars of 9.5 mm diameter, 150 mm long were produced. It was found necessary to add 0.5 at.%Ti to both Ni₃Al and NiAl alloys to obtain adequate wetting. There was a strong tendency for liquid metal infiltration along one side of the fibers causing a shift of the fibers to the opposite side. No interface reaction zone was observed at optical magnifications up to 1000X. A composite of Ni₃Al containing 33 volume percent of FP fibers fractured at 890 MPa which is approximately 3 times the yield strength of the matrix IC-50(21.73A1-0.34Zr-0.IB-Balance Ni at.%) + 0.5 at. %Ti.     

Nb Si基自生复合材料感应熔炼铸锭的组织特征及影响因素

采用氧化钇坩埚真空感应熔炼方法制备了Nb-16Si-22Ti-6Hf和Nb-16Si-22Ti-6Hf-2Cr-2Al合金铸锭, 并在1500 ℃时进行了100 h的热处理。结果表明, 铸态和热处理后的合金均由铌基固溶体(Nb_SS)、Nb₃Si、β-Nb₅Si₃和γ-Nb₅Si₃组成。冷却速度、合金化元素及热处理均会影响合金的组织。冷却速度较低时, 铸锭顶部的组织较粗大; 合金化元素Cr和Al可以促进Nb₃Si的共析转变, 使合金铸锭的组织均匀、细化; 热处理则促进Nb₃Si→Nb₅Si₃+Nb_SS的发生, 且Nb₃Si的尺寸和体积分数均减小, 边界变圆润, Nb_SS枝晶粗化, 共晶组织由片层状变为不规则岛状。      

Fe元素对Nb 16Si原位复合材料显微组织及室温力学性能的影响

采用真空非自耗电弧熔炼方法制备了Nb-16Si-xFe原位复合材料(x = 2, 4, 6, 原子分数(%), 分别简称为2Fe、4Fe、6Fe合金), 研究了Fe含量对Nb-16Si合金的显微组织与室温力学性能的影响。结果表明: 铸态及热处理态(1350 ℃真空退火100 h) 2Fe和4Fe合金主要由Nb基固溶体(Nb_SS)、Nb₃Si和Nb₄FeSi三相组成, 随着Fe含量的增多, Nb₃Si含量减少, 而Nb₄FeSi含量增加, 6Fe合金仅由Nb_SS和Nb₄FeSi两相组成; 热处理后Nb_SS上有细小的硅化物析出; Nb-16Si合金中加入Fe元素后所生成的新相Nb₄FeSi是一个硬脆的硅化物相, 其显微硬度和室温断裂韧性 分别为HV 1110和1.22 MPa·m1/2; 随着Fe含量由2%提高到6%, 热处理态Nb-16Si-xFe合金的室温 断裂韧性呈略微下降趋势, 而硬度和压缩强度呈上升趋势。      

Sintering behavior and microwave dielectric properties of Bi3(Nb1−xTax)O7 solid solutions

Solid solutions of Bi₃(Nb_1−xTa_x)O₇ (x = 0.0, 0.3, 0.7, 1) were synthesized using solid state reaction method and their microwave dielectric properties were first reported. Pure phase of fluorite-type could be obtained after calcined at 700 °C (2 h)⁻¹ between 0 ≤ x ≤ 1 and Bi₃(Nb_1−xTa_x)O₇ ceramics could be well densified below 990 °C. As x increased from 0.0 to 1.0, saturated density of Bi₃(Nb_1−xTa_x)O₇ ceramics increased from 8.2 to 9.1 g cm⁻³, microwave permittivity decreased from 95 to 65 while Q_f values increasing from 230 to 560 GHz. Substitution of Ta for Nb modified temperature coefficient of resonant frequency τ_f from −113 ppm °C⁻¹ of Bi₃NbO₇ to −70 ppm °C⁻¹ of Bi₃TaO₇. Microwave permittivity, Q_f values and τ_f values were found to correlate strongly with the structure parameters of fluorite solid solutions and the correlation between them was discussed in detail. Considering the low densified temperature and good microwave dielectric proprieties, solid solutions of Bi₃(Nb_1−xTa_x)O₇ ceramics could be a good candidate for low temperature co-fired ceramics application.     

Molecular dynamics simulations of amorphisation in Al and Ni3Al

Using Molecular Dynamics and an Embedded Atom Method (EAM) potential derived by Voter and Chen [1] for the Ni---Al binary alloy system, simulations of the crystalline to amorphous transition have been performed in fcc Al and L1₂ Ni₃Al lattices containing approximately 10 000 atoms under shock loading conditions. With tensile stress simulations, at 300 K Al turned amorphous after copious emission of dislocations, while at 10 K it did not become amorphous. The regions of amorphisation were found to be well correlated to high levels of local volume change (ΔV/V = 10%). For the Ni₃Al simulations, only shear stresses were used, and in this case the onset of amorphisation appeared to be triggered by copious dislocation multiplication. Both homogeneous and heterogeneous nucleations were observed and the propagation pattern of the amorphisation transformation very much resembled a percolation process.     

Silicide formation and phase separation from Cu/Nb and Nb/Cu bilayers on silicon

Electron beam evaporation was used to produce Nb/Cu and Cu/Nb bilayers on silicon. The phase sequence and morphology were investigated as a function of annealing temperature in the temperature range between 200 °C and 800 °C, using Auger electron spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, and transmission electron microscopy. Independently of the sequence of deposition, the phases Nb₃Si and Nb₅Si₃ are the two first niobium phases to be formed as a very thin layer at the Nb---Si interface. However, there is evidence that the reaction between niobium and silicon depends strongly on the presence of copper at the Nb---Si interface. The unusual coexistence of Nb₅Si₃, NbSi₂ and niobium phases was also observed. The formation of the ternary phase Nb₅Cu₄Si₄ was detected after annealing Cu/Nb at 700 °C and Nb/Cu at 800 °C. In the latter case the NbSi₂ and Cu₃Si+Cu₄Si phases were formed through a layered growth process.     

Microstructure and strength of brazed joints of Ti3Al-base alloy with NiCrSiB

Brazing of Ti₃Al alloys with the filler metal NiCrSiB was carried out at 1273–1373 K for 60–1800 s. The relationship of brazing parameters and shear strength of the joints was discussed, and the optimum brazing parameters were obtained. When products are brazed, the optimum brazing parameters are as follows: brazing temperature is 1323–1373 K, brazing time is 250–300 s. The maximum shear strength of the joint is 240–250 MPa. Three kinds of reaction products were observed to have formed during the brazing of Ti₃Al alloys with the filler metal NiCrSiB, namely, TiAl₃ (TiB₂) intermetallic compounds formed close to the Ti₃Al alloy. TiAl₃+AlNi₂Ti (TiB₂) intermetallic compounds layer formed between TiAl₃ (TiB₂) intermetallic compounds and the filler metal and a Ni[s,s] solid solution formed in the middle of the joint. The interfacial structure of brazed Ti₃Al alloy joints with the filler metal NiCrSiB is Ti₃Al/TiAl₃ (TiB₂)/TiAl₃+AlNi₂Ti (TiB₂)/Ni[s,s] solid solution/TiAl₃+AlNi₂Ti (TiB₂)/TiAl₃ (TiB₂)/Ti₃Al, and this structure will not change with brazing time once it forms. The formation of over many intermetallic compounds TiAl₃+AlNi₂Ti (TiB₂) results in embrittlement of the joint and poor joint properties. The thickness of TiAl₃+AlNi₂Ti (TiB₂) intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K₀ of the reaction layer TiAl₃+AlNi₂Ti (TiB₂) in the brazed joints of Ti₃Al alloys with the filler metal NiCrSiB are 349 kJ/mol and 24.02 mm²/s, respectively, and the growth formula was y²=24.04exp(−41977.39/T)t. Careful control of the growth of the reaction layer TiAl₃+AlNi₂Ti (TiB₂) can influence the final joint strength.     

High bit density (100 Mb/cm2) with single-layer Co-Crmedia and ring heads in perpendicular magnetic recording

The signal and noise of single-layer Co₇₉Cr₂₁ media are measured with ring heads to estimate the area density that can be achieved. Densities as high as 100 Mb/cm² (1 μm²/bit) are expected when a signal-to-noise ratio sufficient for an error probability less than 10 ^-5 is required. As a comparison, densities estimated from data from metal-evaporated tape and CrO₂ tape are given. In the frequency response of the single-layer media, an additional minimum was observed for a wavelength slightly larger than the gap length. This is probably caused by the bipolar nature of the perpendicular recording field of a ring head     

Nd3+:Lu2O3放电等离子烧结及光学性能

Lu₂O₃是具有高热导率而成为极具潜力的高功率激光介质材料。实验以商用氧化物粉体为原料, LiF为烧结助剂, 采用放电等离子烧结法制备了不同Nd³⁺掺杂浓度(C_Nd=0, 1at%, 3at%和5at%) Lu₂O₃透明陶瓷, 并研究了Nd³⁺掺杂浓度对Lu₂O₃陶瓷的物相、烧结性能、微观结构及光学性能的影响。结果表明：在高Nd³⁺浓度(5at%)掺杂后烧结样品仍为纯Lu₂O₃相;Nd³⁺掺杂对Lu₂O₃陶瓷烧结性能及微观形貌的影响有限;所有样品最终均表现出高致密性(99.5%以上)和优异的透光性能, 其中3at% Nd³⁺:Lu₂O₃的透过率最高, 在1064和2000 nm处的透过率分别为82.7和83.2%。Nd³⁺:Lu₂O₃透明陶瓷的最强发射峰位于1076和1080 nm;且随着Nd³⁺掺杂浓度的增加, 荧光强度降低, 寿命变短, 发生浓度淬灭。     

Performances of metal pigment tapes with 600-700 Oe coercivity

Audio or video recording performances of various magnetic tapes including Co-modified γ-Fe2O3, metal and Fe4N tapes having their coercivity range of 600-700 Oe were investigated. The tapes were prepared by the conventional method using the above magnetic pigments which were prepared to give their coercivity range of 600-800 Oe. The electromagnetic characteristics of the tapes were discussed in comparison with the commercial reference tape. The metal tapes were superior to the other two tapes on Sensitivity (S), Frequency Properties (F), Maximum Output Level (MOL) and Dynamic Range (D.R.) The Fe4N tape has an excellent property on Distortion (THD).     

三元陶瓷Pb(In1/2Nb1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3准同型相界附近组分的介电、铁电和压电性能

铅基复合钙钛矿铁电材料广泛应用于机电传感器、致动器和换能器。二元铁电固溶体Pb(Ni_1/3Nb_2/3)O₃- PbTiO₃(PNN-PT)由于其在准同型相界(MPB)区域具有优异的压电、介电性能而备受关注。然而较大的介电损耗和较低的居里温度限制了其在高温高功率器件方面的应用。本研究通过引入Pb(In_1/2Nb_1/2)O₃ (PIN)作为第三组元改善PNN-PT的电学性能, 提高其居里温度; 通过两步法合成了MPB区域的三元铁电陶瓷Pb(In_1/2Nb_1/2)O₃- Pb(Ni_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PNN-PT), 研究了其结构、介电、铁电和压电性能。制备的所有组分陶瓷具有纯的钙钛矿结构。随着PT含量的增加, 陶瓷结构从三方相转变为四方相。通过XRD分析得到了室温下PIN-PNN-PT体系的MPB相图。体系的居里温度由于PIN的加入得到了很大的提高, 更重要的是PIN的引入降低了PNN-PT体系的介电损耗和电导。MPB处的组分展现出了优异的电学性能, 室温下, 性能最优组分为0.30PIN-0.33PNN-0.37PT: d₃₃=417 pC/N, T_C=200 ℃, ε′= 3206, tanδ=0.033, P_r=33.5 μC/cm², E_C=14.1 kV/cm。引入PNN-PT的PIN第三组元使得体系的居里温度和压电性得到提高的同时降低了的介电损耗和电导率, 因此, PIN-PNN-PT三元铁电陶瓷在高温高功率换能器等方面具备一定的应用潜力。     

Thermomechanical processing and transport current density of Ag-sheathed (Tl,Cr)Sr2(Ca0.9,Pr0.1)Cu2O7 superconductor tapes

Powders with nominal composition (Tl,Cr_0.15)Sr₂(Ca_0.9,Pr_0.1)Cu₂O₇ (Tl-1212) and T_c90 K were used to fabricate Ag-sheathed superconducting tapes employing the powder-in-tube (PIT) method. The tapes were subjected to intermediate mechanical rolling or pressing. Conditions that enhance the transport critical current density (J_c) of the tapes were investigated. Optimum annealing temperature and period together with uniaxial pressing are necessary to increase J_c of the Tl-1212/Ag tapes. Annealing at 910 °C for 0.5–1 h enhanced the 1212 phase formation and improved intergranular connectivity between grains, as well as to provide healing for the fractured structure caused by deformation process. A relatively longer annealing time at higher temperature gave rise to secondary phases and resulted in the decrease of J_c. Mechanical uniaxial pressing greatly densified the tapes core and thus led to closer contact between grains. At liquid nitrogen temperature and zero field, J_c of the pressed tapes annealed at 910 °C for 1 h is 3060±127 A cm⁻². The initial drastic drop of J_c in low fields (<0.06 T) indicates the performance of the tapes is limited by weak links. No significant anisotropic transport properties were observed in applied magnetic field. This is due to the absence of texturing in the tapes as the grains are randomly oriented revealed through SEM micrographs.