Plastic deformation in polycrystalline Nb3Sn

A study of the high temperature plastic deformation of polycrystalline Nb₃Sn has been undertaken on hot isostatically pressed material having grain sizes in the 12 to 60 (μm range. Through compression testing and load-relaxation testing deformation has been studied over a strain rate range from 10⁻⁶to 10⁻²s and a temperature range from 1150 to 1650 °C. Plastic deformation can be observed in compression at 1400 °C and above and extensive deformation is possible at 1650°C. Except for the lowest strain rates at 1650 °C, load-relaxation stress-strain rate relationships are consistent with “power law creep”. Analysis of stress-strain rate-temperature relationships projects an activation energy for creep of very roughly 500 kJ/mol. Observations on yield point behavior and fracture mode transition are presented. A comparison to monocrystalline V₃Si behavior is made, and the role of the sub-structure during testing is considered.     

Facile Synthesis of Nb3Sn Via a Hydrogen Reduction Process

Metallurgical and Materials Transactions B - A controllable and facile process for the preparation of Nb3Sn intermetallic compound nanopowders using NbCl5 and SnCl2 vapors reduced by hydrogen has...     

Effect of oxygen on microstructures of high-rate sputter-deposited Nb3Sn superconductors

The role of excess oxygen and deposition temperature on the microstructure and critical temperature (T _c ) has been studied in high-rate, sputter deposited Nb₃Sn. Excess oxygen does not significantly affect the grain size of the A15 phase whether it is deposited at low temperature followed by annealing or deposited directly at an elevated temperature. Oxygen does promote the formation of the amorphous phase during deposition at low temperature. During subsequent transformation of material sputter deposited at room temperature, gas bubbles form from the entrapped sputtering gas. Excess oxygen also promotes greater precipitate formation during deposition at elevated temperature. In no case was there a large change in the superconducting transition temperatureT _c ; however, the microstructural features may have significant effects on the critical current densityJ _c .     

气相氢还原合成Nb3Sn粉末过程的热力学模拟

基于多元多相平衡原理,建立了氢气还原NbCl5和SnCl2蒸汽合成Nb3Sn超细粉末过程的热力学模型,使用FactSage软件计算了NbCl5,SnCl2的蒸发温度和载气Ar（g）用量,H2（g）用量和还原反应温度、收集温度等关键参数对反应产物的影响。计算结果给出了合成Nb3Sn（s）所需要的蒸发温度与载气使用量的组合、不同还原反应温度时99%转化率时所需要的最小H2（g）用量以及不同收集温度时最终固体产物中杂质的含量。     

Structural characteristics of Nb3Sn produced by three P/M techniques

Powder metallurgical techniques have been applied to the problem of preparing monolithic samples of Nb₃Sn of a homogeneity, density and stability suitable for unambiguous plastic deformation studies. Cold pressing and reaction sintering, infiltration, and hot isostatic pressing (HIP) of Nb and Sn powders have been evaluated, with HIP processing producing a decidedly superior structure. The most homogeneous structure was produced by HIP processing at 1630°C for one h at a pressure of 160 MPa. A continuous matrix of Nb₃Sn was produced with a porosity of 2.6 pct and a secondary phase content of 3.3 pct. The principal secondary phase was NbO and no unreacted Nb remained. The Nb₃Sn matrix was quite homogeneous with microprobe analysis revealing an off-stoichiometric composition of 72.2 to 73.2 pct Nb. An equiaxed grain size of about 60 μm was developed and X-ray diffraction analysis revealed a high degree of long range order. HIP processing at 1200°C produced a finer grain size, increased porosity, and an incompletely reacted structure involving 3.5 pct unreacted Nb. The composition of the Nb₃Sn phase was nearly the same, regardless of processing technique. Considerable evidence of dislocations arrayed in low angle, sub-grain boundaries was observed in the 1630°C HIP processed material. Simple, isolated dislocations were predominant in the 1200°C HIP processed material.     

The Elastic Modulus and Flow Stress of Nb3Sn at Elevated Temperatures

The plastic deformation of Nb₃Sn has been the subject of a number of investigations, and the hot deformation of Nb₃Sn polycrystals has been extensively studied in the 1150 to 1650 °C range.^[1–4] The hot deformation stress-strain rate-temperature relationships are largely those of “power law creep”, with activation energies for creep roughly in the 400 to 500 kJ/mol range.^[2,3] Grain size refinement increases flow stress in the power law creep regime.^[3] Hot deformed Nb₃Sn displays polygonized dislocation structure.^[5]     

Features of plastic flow of powder Al-40Sn alloy during extrusion

Features of compaction by means of the extrusion of powders of Al-40Sn alloy are investigated. Compaction is carried out in a temperature range of 25–230°C at a reduction coefficient of 4.5 (ɛ = 1.5). An investigation into the structure along the length of a sample, including the butt end, has shown that the main part of its change occurs at the steps of formation of a billet and upon the placement of the latter within an operating channel of a press mold for extrusion. Under pressure operation in this period of time, a new composite material is formed which consists of aluminum particles dispersed into an unbroken soft tin matrix. As such material is forced through the die, tin strata act as an interparticle lubricant, making the mutual displacement of aluminum particles, which do not deform much as a result, easier. As a consequence, oxide films on aluminum particles remain and prevent the establishment of strong interfaces. The extruded material contains cracks along interfaces and shows low plasticity.     

Fabrication and evaluation of Nb/Nb5Si3 microlaminate foils

Alloys of Nb and Nb₅Si₃, and in particular Nb/Nb₅Si₃ microlaminates, have potential as high-temperature materials. In this study, microlaminates of Nb and amorphous Nb-37.5 at. pct Si are magnetron sputter deposited from elemental Nb and polycrystalline Nb₅Si₃ targets. The microlaminates are heat treated at high temperatures to produce crystalline layers of Nb and Nb₅Si₃ that are flat, distinct, and stable for at least 3 hours at 1200 °C. The layers consist of textured Nb grains and equiaxed submicron Nb₅Si₃ grains. Initial room-temperature tensile tests indicate that the microlaminates have strengths similar to cast and extruded alloys of Nb and Nb₅Si₃. The fracture mode of the Nb layers is dependent on the Nb layer thickness, with thin layers failing in a ductile manner and thick layers failing by cleavage. The Nb layers bridge periodic cracks in the Nb₅Si₃ layers, and using a shear lag analysis, the tensile strength of Nb₅Si₃ is estimated. The results indicate that microstructurally stable and mechanically robust microlaminates of Nb and Nb₅Si₃ can be fabricated by sputter deposition with a high-temperature heat treatment. The processing, microstructure, and mechanical properties of these microlaminates are discussed.     

The stability of Nb/Nb5Si3 microlaminates at high temperatures

The microstructural, phase, and chemical stability of Nb/Nb₅Si₃ microlaminates was investigated at temperatures ranging from 1200 °C to 1600 °C. Freestanding Nb/Nb₅Si₃ microlaminates were prepared by sputter deposition and their stability was investigated by annealing either in vacuum or in an Ar atmosphere. The microlaminates were generally structurally stable, with no evidence of layer pinchoff, even after annealing at 1600 °C. However, a small volume fraction (<2 pct) of voids formed in the silicide layers at 1500 °C and 1600 °C, which are attributed either to the Kirkendall diffusion of Si or to the growth of silicide grains. In terms of phase stability, there was no discernible dissolution of the Nb₅Si₃ layers and no silicide precipitates in the Nb layers following anneals at 1400 °C. Annealing at higher temperatures, though, resulted in the formation of non-equilibrium Nb₃Si on the Nb/Nb₅Si₃ interfaces. This phase is thought to precipitate from the supersaturated Nb-Si solid solution on cooling, and is stabilized by the development of tensile stresses in the Nb layers. The most pervasive observed high-temperature breakdown mechanism was chemical in nature, namely, the loss of Si via sublimation to the environment. The Si loss was partially suppressed either by annealing in a Si-rich atmosphere or by annealing in Ar.     

粉末冶金制备的Ti35Nb2．5Sn5HA生物复合材料的组织与性能研究

采用高能机械球磨和脉冲电流活化烧结方法制备了一种新型的不含Al、V等有毒元素的口钛合金基体的Ti35Nb2．5Sn5HA生物复合材料。研究了不同机械球磨时间球磨的Ti35Nb2．5Sn5HA粉末以及用这几种粉末烧结制备的样品微观组织和显微硬度变化,球磨时间对烧结复合材料的微观组织和性能的影响。结果表明：随着球磨时间的增加,Ti35Nb2．5Sn5HA粉末的颗粒尺寸逐渐减小,Nh和Sn开始与Ti发生固溶,形成Ti的过饱和固溶体,而且α-Ti也开始向β-Ti转化。当球磨时间达到12h,球磨粉末中α-Ti完全转化为β-Ti,粉末颗粒的平均尺寸为500nm左右。12h球磨的粉末烧结制备的复合材料具有超细晶粒尺寸,晶粒平均尺寸为200nm,这种复合材料的维氏显微硬度可以达到10187．3MPa。     

Strength and ductile-phase toughening in the two-phase Nb/Nb5Si3 alloys

The effect of heat treatment on the mechanical properties of Nb-Nb₅-Si₃ two-phase alloys having compositions Nb-10 and 16 pct Si (compositions quoted in atomic percent) has been investigated. This includes an evaluation of the strength, ductility, and toughness of as-cast and hot-extruded product forms. The two phases are thermochemically stable up to ∼1670 °C, exhibit little coarsening up to 1500 °C, and are amenable to microstructural variations, which include changes in morphology and size. The measured mechanical properties and fractographic analysis indicate that in the extruded condition, the terminal Nb phase can provide significant toughening of the intermetallic Nb₅Si₃ matrix by plastic-stretching, interface-debonding, and crack-bridging mechanisms. It has been further shown that in these alloys, a high level of strength is retained up to 1400 °C.     

Nb_3Al超导材料的制备与应用

阐述了Nb3Al超导材料的主要制备技术及其在核能、核磁共振、高能加速器各领域中的应用。Al5型金属间超导化合物Nb3Al具有很高的上临界磁场(Bc2)和高场临界电流密度(Jc)。在强磁场下,Nb3Al具有比已实用化的Nb3Sn线材更好的抗应力特性和类似于Nb3Sn的辐照敏感性。Nb3Al作为大型核聚变反应堆用磁体材料有着很好的应用前景。随着Nb3Al超导材料的不断发展,它将越来越多地用于尖端技术中,可解决未来能源、交通、医疗和国防事业中的重要问题。