First-principles Study on Structure and Hardness of the RuB2

采用原位法粉末装管工艺( in-situ PIT)制备了无定形碳掺杂MgB2/Nb/Cu超导线材并研究了该掺杂对MgB2微观结构及超导电性的影响.复合线材中以Nb作为阻隔层、Cu作为稳定体并采用冷拉拔工艺进行加工.研究了无定形碳掺杂对MgB2相形成、微观结构及超导电性的影响,其中掺杂量分别为MgB2-xCx(x=0.0,0.05,0.08,0.10,0.15).分别采用XRD、SQUID、SEM/EDS及传输电流测试等方法对MgB2/Nb/Cu线材进行分析测试.XRD分析结果显示,700℃热处理后的线材可以获得纯度较高的MgB2超导相;微观结果照片显示无定形碳掺杂后可以获得良好的晶粒连接性;能谱分析表明掺杂物C元素均匀的分布在MgB2基体中;通过四引线法测试了传输临界电流密度Jc,在4.2 K、5T,其Jc值高达1.4×105 A/cm2;在4.2K、10T,其Jc值为3.3×104A/cm2.     

Cu互连中Zr嵌入层对ZrN阻挡层热稳定性的影响

在不同的衬底偏压下,用射频反应磁控溅射的方法在Si(100)衬底和Cu膜间制备了ZrN/Zr/ZrN堆栈结构的阻挡层。研究了Zr层的插入对ZrN扩散阻挡性能的影响,结果表明:随着衬底偏压的升高,阻挡层的电阻率降低,ZrN呈(111)择优取向;Zr层的插入使ZrN阻挡层的失效温度至少提高100℃,750℃仍能有效地阻止Cu的扩散,阻挡性能提高的主要原因可能是高温退火时形成的ZrO2阻塞了Cu快速扩散的通道。     

TiC掺杂12芯MgB2线材微观结构以及超导电性

采用 PIT工艺,以分步法粉末为装管前驱粉,选用中心铜铌复合棒增强的导体结构制备了TiC掺杂MgB2多芯线材,研究了不同热处理温度对于粉末相组成、线材的微观结构以及超导电性的影响,结果表明分步法粉末能够有效提高C原子的取代水平,同时芯丝中MgB2晶粒尺寸达到亚微米级,MgB2晶粒连结性较好,制备多芯线材在4.2 K,5 T时,其Jc仍高达3×104 A/cm2。     

Interfacial Microstructure and Its Influence on Resistivity of Thin Layers Copper Cladding Steel Wires

The interfacial microstructure and resistivity of cold-drawn and annealed thin layers copper cladding steel (CCS) wires have been systematically investigated by the methods of scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and resistivity testing. The results showed that the Cu and Fe atoms near interface diffused into each other matrixes. The Fe atoms diffused into Cu matrixes and formed a solid solution. The mechanism of solid solution is of substitution type. When the quantity of Fe atoms exceeds the maximum solubility, the supersaturated solid solution would form Fe clusters and decompose into base Cu and α-Fe precipitated phases under certain conditions. A few of α-Fe precipitates was observed in the copper near Cu/Fe interfaces of cold-drawn CCS wires, with 1–5 nm in size. A number of α-Fe precipitates of 1–20 nm in size can be detected in copper near Cu/Fe interfaces of CCS wires annealed at 850°C. When annealing temperature was less than 750°C, the resistivity of CCS wires annealed was lower than that of cold-drawn CCS wires. However, when annealing temperature was above 750°C, the resistivity of CCS wires was greater than that of cold-drawn CCS wires and increased with rising the annealing temperature. The relationship between nanoscale α-Fe precipitation and resistivity of CCS wires has been well discussed.     

Diffusion Barrier Selection from Refractory Metals (Zr,Mo and Nb) Via Interdiffusion Investigation for U-Mo RERTR Fuel Alloy

U-Mo alloys are being developed as low enrichment monolithic fuel under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Diffusional interactions between the U-Mo fuel alloy and Al-alloy cladding within the monolithic fuel plate construct necessitate incorporation of a barrier layer. Fundamentally, a diffusion barrier candidate must have good thermal conductivity, high melting point, minimal metallurgical interaction, and good irradiation performance. Refractory metals, Zr, Mo, and Nb are considered based on their physical properties, and the diffusion behavior must be carefully examined first with U-Mo fuel alloy. Solid-to-solid U-10 wt.%Mo versus Mo, Zr, or Nb diffusion couples were assembled and annealed at 600, 700, 800, 900 and 1000 °C for various times. The interdiffusion microstructures and chemical composition were examined via scanning electron microscopy and electron probe microanalysis, respectively. For all three systems, the growth rate of interdiffusion zone were calculated at 1000, 900 and 800 °C under the assumption of parabolic growth, and calculated for lower temperature of 700, 600 and 500 °C according to Arrhenius relationship. The growth rate was determined to be about 10³ times slower for Zr, 10⁵ times slower for Mo and 10⁶ times slower for Nb, than the growth rates reported for the interaction between the U-Mo fuel alloy and pure Al or Al-Si cladding alloys. Zr, however was selected as the barrier metal due to a concern for thermo-mechanical behavior of UMo/Nb interface observed from diffusion couples, and for ductile-to-brittle transition of Mo near room temperature.     

结合连续管线成型技术和粉末套管法制备SiC掺杂的MgB_2超导线材研究

结合连续管线成型技术和粉末套管方法,原位掺杂SiC制备出了20m长的单芯MgB2/Fe、MgB2/Nb/Fe线材和7芯、19芯及49芯的MgB2/Nb/Cu/Fe复合多芯线材。采用XRD和SEM分别对烧结后样品芯部进行相成分和微观结构研究,并通过TEM对SiC掺杂的机理进行了简单分析。采用四引线法对线材进行电流测量并获得临界电流密度。结果表明,线材经过不同温度保温15min的真空退火后,在800℃形成的MgB2相含量最高,其中单芯MgB2/Fe线材在4.2K,11T下Jc值超过104A/cm2,7芯复合线材在4.2K,7.5T下Jc值也达到104A/cm2,并且具有较好的热稳定性,在低场下仍可稳定通过电流。     

Nb/Mn/Si合金化的β-γ钛铝合金循环氧化行为（英文）

利用扫描电子显微镜、电子探针、电子背散射衍射和X射线衍射,研究Ti42Al1.5Mn3Nb0.1B合金和Ti42Al1.5Mn3Nb0.1B0.2C0.2Si合金在750～850℃下的循环氧化行为。两种合金的氧化增质曲线大致符合抛物线规律,且在800℃的氧化速率常数较Ti42Al5Mn1W合金的降低。在所有的实验温度下,两种合金表面都生成保护性良好的氧化膜,没有开裂或剥落发生。Nb的添加会抑制TiO₂的生长,促进Al的选择性氧化,使合金形成致密的Al₂O₃层。另外,微量Si元素的添加进一步提高合金的抗氧化性,使其生成更为致密的Al2O3层,在氧化过程中进一步抑制氧的内扩散,降低合金的氧化增质,且其效果在高温下更加明显。     

EDX and ion beam treatment studies of filamentary in situ MgB2 wires with Ti barrier

In situ SiC-doped filamentary MgB₂ wires (with the diameter of 0.860 and 0.375 mm) with Cu stabilization separated by Ti barrier layers supported by outer SS sheath and annealed at 800 °C/0.5 h have been studied by combination of EDX analysis and ion beam selective etching. It was found that several Ti-Cu inter-metallic compounds were created by Cu-Ti interdiffusion and thus the barrier protection against Cu penetration into the superconducting filaments is limited. We showed an advantage of Ti use as the barrier material in our wires. Ti getters silicon out from the superconducting filament, what purges superconducting MgB₂ from Si and creates an additional Si-rich layer in inner part of Ti barrier which prevents Cu diffusion more effectively.     

反应烧结Ti-22Al-25Nb合金的高温氧化行为

Ti-22Al-25Nb是一种高温结构材料,它的抗氧化性对今后的发展和应用具有重要意义。采用元素粉末和反应烧结法制备了Ti-22Al-25Nb烧结合金,研究了其在静态空气中的氧化行为(923~950℃温度范围内)。不同温度(650 °C, 750 °C, 850 °C, 950 °C)下的最大增重分别为0.15 mg﹒cm-2、0.41 mg·cm-2、1.68 mg·cm-2和6.9 mg·cm-2。研究发现Ti-22Al-25Nb烧结合金具有良好的抗氧化性,特别是在750°C以下（950°C时发生氧化分解）。根据氧化动力学分析,在750℃以下,氧化行为大致遵循抛物线规律,而在850℃以上,氧化行为符合线性规律。讨论了铌合金元素对氧化动力学的影响,通过对氧化形态和相的观察和分析,证明O相（有序Ti2AlNb相）的抗氧化性能优于其它相,其原因可以解释为不同相的Nb含量的差异导致抗氧化性的差异。     

Nb、Cu金属层厚度对Si3N4/Nb/Cu/Ni/Incone l600接头组织和性能的影响

采用Nb／Cu／Ni作中间层，在连接温度为1403K、连接时间为50min、连接压力为7．5MPa的条件下，采用不同尺寸的中间层进行了Si3N4陶瓷与Inconel 600高温合金的部分液相扩散连接。通过改变Nb层、Cu层厚度，研究了Cu层、Nb层厚度变化对Si3N4／Nb／Cu／Ni／Inconel 600接头的组织和性能的影响。研究发现，当Cu层厚度小于0．05mm时，随着Cu层厚度的增加，接头中的Cu—Ni合金层厚度增加，接头强度快速增加；当Cu层厚度超过0．05mm时，接头中的Cu—Ni合金层厚度由于压力的作用不明显增加，接头强度增加缓慢。随着Nb层厚度的增加，反应层厚度增加，接头的强度先增大后减小。     

Isothermal oxidation behavior of powder metallurgy beta gamma TiAl–2Nb–2Mo alloy

A new TiAl–2Nb–2Mo beta gamma alloy was synthesized by powder metallurgy process. HIP’ed and vacuum heat treated specimens were isothermally oxidized at 800 °C and 900 °C in air up to 500 h. The TiAl–2Nb–2Mo alloy oxidized parabolically up to 500 h at both 800 °C and 900 °C. The oxides consisted of outer TiO₂ layer, intermediate Al₂O₃ layer, and inner TiO₂ rich mixed layer and the oxidation mechanisms of the alloy were identical at both temperatures. During oxidation, the degradation of lamellar colonies formed a diffusion zone just below the oxide/substrate interface consisting of γ-TiAl matrix and dispersed beta phases which contained high concentration of Nb and Mo. The oxidation rate of the TiAl–2Nb–2Mo alloy is more sensitive to temperature than those of the Ti–48Al–2Nb–2Cr and Ti–48Al–2Nb–2Cr–W alloys.     

Effects of C10H8 Doping on Microstructure and Superconductivity of MgB2 Wires

采用原位粉末装管技术(in-situ PIT)制备了萘(C10H8)掺杂MgB2/Nb/Cu线材。前驱粉末按照MgB2+xwt% (x=0,2,5,8)的比例将Mg粉、B粉和C10H8粉末混合研磨,装入Cu/Nb复合管中,分别拉拔加工至Φ2.0 mm和Φ1.0 mm,然后Ar气氛中分别在650,700,750 ℃热处理,保温2.5 h。通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)和能谱仪(EDS)等测试手段分析了样品的相结构和微观结构等。结果发现,样品超导转变温度Tc不随萘掺杂量的变化而变化,但正常态电阻有所降低。在20和25 K无外磁场时,x=8样品的临界电流密度分别达到1.1×105和3.8×104 A/cm2,而x=5样品也达到3.1×104 和 1.2×104 A/cm2。     

Effect of tin addition on Nb–Si-based in situ composites. Part II: Oxidation behaviour

This paper reports the effects of adding from 2 to 8 at.% tin on the oxidation behaviour of Nb/Nb₅Si₃ composites at 815 °C and at higher temperatures (1100 and 1200 °C). The role of tin in the elimination of pesting and in the oxidation process at high temperatures was established. The consumption of elements with a higher affinity for oxygen than Sn induces the accumulation of tin at the oxide/internal oxidation zone boundary. Low melting point phases (NbSn₂ and/or pure Sn) form at 815 °C, whereas a layer of M₅Si₃ and Nb₅SiSn₂ forms at 1100 and 1200 °C. Once these products are formed, they generate an oxygen diffusion barrier and allow the elimination of pesting. However, for long oxidation processes at 1100 °C, the oxidation rate of Nb/Nb₅Si₃ composites containing tin should be higher than that for tin-free composites. Moreover, some oxidation results have suggested that the presence of A15-(Nb,Ti)₃(Sn,Ti) in the microstructure of composites with at.%Sn > 2 can severely impact the low temperature fracture toughness of these composites.     

Texture and Anisotropy of Jc of ex situ MgB2/Fe Mono—Filamentary Tapes

采用不同粒度的初始MgB2粉末，通过粉末套管法技术制备出非原位单芯MgB2／Fe超导带；测量了不同磁场和温度下MgB2／Fe带的以值．结果表明；Jc具有各向异性，其各向异性的大小受初始粉末尺寸的影响．对剥离铁包套后MgB2芯的XRD图拟合分析表明，MgB2均显示轻微的织构，MgB2／Fe界面处的织构稍强．MgB2的再结晶晶粒尺寸随初始粉末尺寸的增大而增大．讨论了粉末粒度和织构度与Jc各向异性的关联性．     

Interfacial microstructure and mechanical properties of GH99 superalloy and Nb brazed joint using Cu75Pt25 filler

Cu75Pt25 brazing filler was applied to brazing GH99 superalloy to Nb, and the sound joints were obtained by adjusting brazing parameters. The typical interfacial microstructure of the brazed joint was Nb/Nb₇Ni₆+NbNi₃/ Ni(s,s)+Cr-rich NbNi₃+(NbCr₂+NbNi₃)/GH99. The effects of brazing temperature and holding time on the interfacial microstructure of GH99/Cu75Pt25/Nb joints were studied. The results showed that the solution and diffusion of Ni atoms from GH99 substrate into brazing seam played a critical role in the interfacial microstructure evolution. As the brazing temperature rose, the Nb–Ni reaction layer was formed instead of the initial Nb₃Pt layer, and the thickness increased firstly and then remained constant. The highest shear strength of the joint reached 152 MPa when brazed at 1150 °C for 15 min. All of the joints presented a brittle fracture mode during shear test, and the fracture location changed from Nb₃Pt layer to Nb–Ni compounds layer.     

First trial of pulse electric current sintering for high-temperature material Ir3Nb

Pulse electric current sintering (PECS) was tried for Ir-25 at.% Nb (Ir₃Nb), which has a high melting temperature of about 2435 °C. Ingot powder was made by crashing an ingot, and the ingot powders were sintered at temperatures between 1700 and 1900 °C up to 2 h under 40 MPa. Pure-metal powder was mixed to achieve a composition of Ir-25 at.% Nb, and the pure-metal powders were sintered at a temperature between 1700 and 1900 °C for up to 1 h. The microstructure and phase structures of sintered samples were investigated by scanning electron microscopy (SEM) and x-ray diffractometry. The sintering mechanism and problems for Ir₃Nb in PECS are discussed.     

Transmission electron microscopy study of the failure mechanism of the diffusion barriers (TiN and TaN) between Al and Cu

Failure mechanisms of transition metal nitride thin film diffusion barriers, such as TiN and TaN (10 nm in thickness), between Al and Cu were investigated by transmission electron microscopy (TEM), scanning transmission electron microscopy, and energy dispersive spectroscopy. After annealing at 450 °C during 30 min, the TiN diffusion barrier initially failed due to an interfacial reaction between TiN and Al forming TiAl3. When the annealing temperature was increased to 500 °C, Cu-Al intermetallic compounds were formed by the interdiffusion of Al and Cu through the diffusion barrier. In the case of the Al/TaN/Cu structure, no interfacial reaction products were observed after annealing up to 550 °C. On the other hand, it failed after annealing at 550 °C due to the inter-diffusion of Cu and Al through the diffusion barrier. TEM also identified Cu to be the rapid diffusing species in both systems. The results are discussed based on the thermodynamic stability of the interface predicted by the ternary phase diagram and the diffusion kinetics of Al and Cu through the diffusion barrier. The results show that both the thermodynamic stability of the diffusion barrier between Al and Cu and the diffusion kinetics of Al and Cu through the diffusion barrier, which are dependent on the microstructure of the diffusion barrier, should be considered carefully when selecting diffusion barrier materials between Al and Cu.     

Solid state amorphization in cold drawn Cu/Nb wires

The microstructure of cold drawn Cu/Nb nanocomposite wires was investigated using a three dimensional atom probe (3D-AP) and transmission electron microscopy (TEM). Although there is no solubility between Nb and Cu in the equilibrium state, atom probe analysis results revealed that intermixing occurs between Nb and Cu filaments as a result of cold drawing with a large strain. High resolution transmission electron microscopy (HRTEM) results revealed that an amorphous layer is formed along some Cu/Nb interfaces. This solid state amorphization is compared with similar reactions observed in Cu–Nb multilayers.     

Temperature dependence of copper diffusion in different thickness amorphous tungsten/tungsten nitride layer

The amorphous W/WN films with various thickness (10, 30 and 40 nm) and excellent thermal stability were successfully prepared on SiO₂/Si substrate with evaporation and reactive evaporation method. The W/WN bilayer has technological importance because of its low resistivity, high melting point, and good diffusion barrier properties between Cu and Si. The thermal stability was evaluated by X-ray diffractometer (XRD) and Scanning Electron Microscope (SEM). In annealing process, the amorphous W/WN barrier crystallized and this phenomenon is supposed to be the start of Cu atoms diffusion through W/WN barrier into Si. With occurrence of the high-resistive Cu₃Si phase, the W/WN loses its function as a diffusion barrier. The primary mode of Cu diffusion is the diffusion through grain boundaries that form during heat treatments. The amorphous structure with optimum thickness is the key factor to achieve a superior diffusion barrier characteristic. The results show that the failure temperature increased by increasing the W/WN film thickness from 10 to 30 nm but it did not change by increasing the W/WN film thickness from 30 to 40 nm. It is found that the 10 and 40 nm W/WN films are good diffusion barriers at least up to 800°C while the 30 nm W/WN film shows superior properties as a diffusion barrier, but loses its function as a diffusion barrier at about 900°C (that is 100°C higher than for 10 and 40 nm W/WN films).     

The kinetics of Nb(C,N) precipitation during the isothermal austenite to ferrite transformation in a low-carbon Nb-microalloyed steel

The kinetics of Nb(C,N) precipitation occurring during the isothermal ferritic (α) transformation were quantitatively measured, along with the transformation kinetics at intercritical temperatures ranging from 710 to 790 °C in a Nb-microalloyed steel by means of electrical resistivity and dilatometry. The precipitation occurred most rapidly at 750 °C, which corresponds to a bay temperature on the start curve of the ferritic transformation of the transformation–time–temperature diagram. While interphase precipitation was observed at and above the bay temperature, precipitation in the α matrix was predominantly below the bay temperature. However, precipitation in the untransformed austenite (γ) matrix during the ferritic transformation was also observed, regardless of the intercritical temperatures. It is suggested that the precipitation occurring in the untransformed γ matrix during the ferritic transformation was accelerated owing to carbon enrichment from the α matrix to the γ matrix during the ferritic transformation. The average size of Nb(C,N) particles observed in the α matrix was slightly larger than that of the γ matrix at a given intercritical temperature. This result is proposed to arise primarily from the rapid diffusion of solute Nb atoms in the body-centered cubic α matrix.