Microstructure of Nb3 (AlSiB) superconducting tapes with extremely high critical current densities

1989 ◽  
Vol 4 (3) ◽  
pp. 526-529 ◽  
Author(s):  
Mireille Treuil Clapp ◽  
Zhang Jian ◽  
Tariq Manzur
Keyword(s):  
Critical Current ◽  
Melt Spinning ◽  
Quenching Rate ◽  
Fine Grained ◽  
Annealing Conditions ◽  
Second Phases ◽  
Current Densities ◽  
Rapidly Solidified ◽  
Equiaxed Grains ◽  
A15 Phase

Alloys of Nb73Al12Si14.5B0.5 were rapidly solidified into amorphous ribbons using the melt spinning technique. These were isothermally annealed at temperatures ranging from 660 to 780 °C. The A15 phase began to crystallize at 700 °C and small amounts of second phases appeared at the higher temperatures. Crystallization was dependent on quenching rate as well as annealing conditions. Below 750 °C nucleation was nonuniform and was enhanced by surfaces and quenched-in nuclei. Above 750 °C nucleation became more uniform and completely crystalline ribbons with equiaxed grains ∼30 nm in diameter were obtained. These ultra fine grained ribbons had extremely high superconducting critical current densities of 8 × 1010 A/m2 and 5 × 1010 A/m2 at magnetic fields of 0.5 and 15 tesla, respectively, at 4.2 K.

Effect of refractory elements on microstructure and fracture of rapidly solidified nickel base alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 934-935
Author(s):  
P. Adeva ◽  
J.L. González-Carrasco ◽  
J. Ibáñez ◽  
M. Aballe
Keyword(s):  
Melt Spinning ◽  
Initial Strain Rate ◽  
Gauge Length ◽  
Helium Atmosphere ◽  
Average Area ◽  
Refractory Elements ◽  
Nickel Base ◽  
Rapidly Solidified ◽  
Equiaxed Grains ◽  
Cast Condition

In order to evaluate the effect of refractory elements on the microstructure and properties, and especially on ductility of nickel- base rapidly solidified materials, three rapidly solidified alloys have been obtained by melt spinning under helium atmosphere of 0.04 Pa at linear speed of 47 ms-1 in the form of smooth 20 ∼30 ∼m thick and ∼1 mm wide ribbons. Starting materials were inert gas induction melted alloys with 12 at.% Cr and 20 at.% A1, with additions of 1.5 at.% Nb, 1.5 at.% Ta or 1.9 at.% Mo respectively, balance nickel. Samples were observed by AEM and EPMA in the as-cast condition, and by SEM-EPMA after mechanical testing at temperatures between 300 and 773K. Tensile specimens were suitable ribbon lengths with gauge length 16 mm, and initial strain rate was 10-4s-1. Results were compared with those previously obtained on a similar alloy not containing refractory elements (Ni - 15 at.% Cr - 20 at.% Al).Longitudinal sections show columnar through thickness grains (Fig.l) and in some cases equiaxed grains in the region close to the gas side. The free surface shows grains and cells with an average area in the prepared section of ∼3 μm2 and 0.8 μm2 approximately, as measured by quantitative metallography.

Influence of W additions in rapidly solidified nial

1987 ◽  
Vol 45 ◽  
pp. 212-213
Author(s):  
I. E. Locci ◽  
M. V. Nathal
Keyword(s):  
Low Temperature ◽  
Melt Spinning ◽  
Matrix Composition ◽  
X Ray ◽  
Fine Grained ◽  
Free Jet ◽  
High Temperature Structural Material ◽  
Low Temperature Toughness ◽  
Pure Metals ◽  
Rapidly Solidified

The B2 aluminide NiAl has potential as a high temperature structural material, although its lack of low temperature toughness is a major obstacle. One strategy for improving low temperature toughness is by grain refinement. Fortunately, fine grained intermetallics appear to retain their strengths to much higher fractions of their melting point than do pure metals and alloys. The purpose of this study was to investigate the effects of melt spinning and small W additions on the grain size and stability of NiAl.Two alloys of the same matrix composition, equiatomic NiAl, were examined. One also contained 0.5 W at% (NiAl+W). The alloys were cast as ribbon ∼45 pm thick by ∼2.5 mm wide using a free jet melt spinning apparatus. To simulate consolidation conditions, sections of ribbon were annealed for 1 hour at either 1273 or 1573 °K in purified argon. Optical, X-ray and electron analyses of the as-spun and annealed ribbons were performed.

scholarly journals Microstructural Characterization and Mechanical Properties of Rapidly Solidified Al-Si Systems by Chill Block Melt-Spinning Technique.

2020 ◽  
Vol 17 ◽  
pp. 79-91
Author(s):  
Amal Elsherif ◽  
Mustafa Kamal ◽  
Rizk Mostafa Shalaby
Keyword(s):  
Melt Spinning ◽  
Applied Load ◽  
Microstructural Characterization ◽  
Fine Grained ◽  
Chill Block ◽  
Rapidly Solidified ◽  
Hardness Values ◽  
Microstructural Examination ◽  
Solidification Technology ◽  
Rapid Solidification Technology

AlـSi alloys with compositions (0, 0.1, 0.5, 0.9 and 1.3 wt.% Si) were manufactured by chill block melt spinning method. The resulting ribbons samples have been characterized by xـray diffraction (XRD) and scanning electron microscope (SEM). Detailed analysis of (XRD) shows that presence of f.c.c Al solid solution and Si particles embedded within the aluminum grains. Microstructural examination resulted that microstructure of the melt spun ribbons are more fine and uniformly distributed. Rapid solidification technology led to increase the solubility of Si in αـAl as confirmed by XRD. Micro hardness measurements were also carried out by Vickers microـhardness tester at applied load 25gm forced and different dwell time. It is concluded that the Vickers hardness values are sensitive to applied load and indentation time. It is also found that the highest values of Hv is sensitive to presence of Si as columnar shape with fine grained of Al by high cooling rate.

Microstructure of Rapidly Solidified Al-Si Exhibiting Enhanced Superconducting Properties

1985 ◽  
Vol 62 ◽  
Author(s):  
M. A. Noack ◽  
A. J. Drehman ◽  
A. R. Pelton
Keyword(s):  
Melt Spinning ◽  
Thick Layer ◽  
Bottom Surface ◽  
Superconducting Transition ◽  
Superconducting Properties ◽  
Fine Grained ◽  
Melt Spun ◽  
The Matrix ◽  
Rapidly Solidified ◽  
Insight Into

ABSTRACTTsuei and Johnson previously reported significantly enhanced superconducting transition temperatures for rapidly solidified Al-Si alloys. Here we report a microstructural study of melt spun Al80 Si20 ribbons to determine the mechanism responsible for this enhancement.Results of this investigation revealed three distinct microstructures from the top surface to the more rapidly cooled bottom surface (which was in contact with the melt-spinning wheel). Near the top, the microstructure is of hypoeutectic morphology even though this is a hypereutectic alloy. The predominant microstructure is cellular. A 1 to 3 Wm thick layer at the bottom of the ribbon was found to be responsible for the largest enhancement. This layer is composed of fine-grained supersaturated fcc Al containing densely distributed dc Si precipitates. Microdiffraction analysis revealed a cube/cube orientation relationship between the precipitates and the matrix. These results provide insight into the possible mechanism for the enhancement.

A two-powder process for Bi-2223 precursors

1996 ◽  
Vol 11 (1) ◽  
pp. 28-38 ◽  
Author(s):  
T. G. Holesinger ◽  
K. V. Salazar ◽  
D. S. Phillips ◽  
B. L. Sargent ◽  
J. K. Bremser ◽  
...  
Keyword(s):  
Critical Current ◽  
Grain Growth ◽  
The Other ◽  
Fine Grained ◽  
Current Densities ◽  
Precursor Route ◽  
Blending Process ◽  
Multi Phase

A two-powder process is described for the production of uniform, fine-grained Bi2Sr2Ca2Cu3Oy (Bi-2223) powders. One powder is the Bi2.1−xPbxSr1.9−yCayOz (2:2 Cu-free) phase. The other is a multi-phase powder of approximate overall composition SrCaCu3Oy. The 2:2 Cu-free is one of the first Bi-containing phases to form from a nominal Bi-2223 mixture of oxides and carbonates. This precursor route was chosen for investigation because (1) the powders have very similar particle morphologies and (2) the mixing volumes are closely matched. Both of these characteristics facilitate the milling and blending process. This precursor mix was found to be stable in that explosive grain growth of undesirable phases was not observed during sintering. Critical current densities up to 26,900 A/cm2 in self field at 75 K were obtained in tapes.

EM of rapidly solidified permanent magnets

1992 ◽  
Vol 50 (1) ◽  
pp. 198-199
Author(s):  
Raja K. Mishra
Keyword(s):  
Melt Spinning ◽  
Permanent Magnets ◽  
Dark Field Image ◽  
Dark Field ◽  
Maximum Energy ◽  
Quench Rate ◽  
Maximum Energy Product ◽  
Energy Product ◽  
Annular Dark Field ◽  
Rapidly Solidified

The discovery of a new class of permanent magnets based on Nd2Fe14B phase in the last decade has led to intense research and development efforts aimed at commercial exploitation of the new alloy. The material can be prepared either by rapid solidification or by powder metallurgy techniques and the resulting microstructures are very different. This paper details the microstructure of Nd-Fe-B magnets produced by melt-spinning.In melt spinning, quench rate can be varied easily by changing the rate of rotation of the quench wheel. There is an optimum quench rate when the material shows maximum magnetic hardening. For faster or slower quench rates, both coercivity and maximum energy product of the material fall off. These results can be directly related to the changes in the microstructure of the melt-spun ribbon as a function of quench rate. Figure 1 shows the microstructure of (a) an overquenched and (b) an optimally quenched ribbon. In Fig. 1(a), the material is nearly amorphous, with small nuclei of Nd2Fe14B grains visible and in Fig. 1(b) the microstructure consists of equiaxed Nd2Fe14B grains surrounded by a thin noncrystalline Nd-rich phase. Fig. 1(c) shows an annular dark field image of the intergranular phase. Nd enrichment in this phase is shown in the EDX spectra in Fig. 2.

Facet Topography and Dislocation Structure as a Possible Source for Electrical Heterogeneity in [001] TILT Bicrystals of YBa2Cu3O7-δ

1996 ◽  
Vol 54 ◽  
pp. 338-339
Author(s):  
I-Fei Tsu ◽  
D.L. Kaiser ◽  
S.E. Babcock
Keyword(s):  
Grain Boundary ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Electromagnetic Properties ◽  
Length Scale ◽  
Density Values ◽  
Current Densities ◽  
Applied Fields ◽  
A Current

A current theme in the study of the critical current density behavior of YBa2Cu3O7-δ (YBCO) grain boundaries is that their electromagnetic properties are heterogeneous on various length scales ranging from 10s of microns to ˜ 1 Å. Recently, combined electromagnetic and TEM studies on four flux-grown bicrystals have demonstrated a direct correlation between the length scale of the boundaries’ saw-tooth facet configurations and the apparent length scale of the electrical heterogeneity. In that work, enhanced critical current densities are observed at applied fields where the facet period is commensurate with the spacing of the Abrikosov flux vortices which must be pinned if higher critical current density values are recorded. To understand the microstructural origin of the flux pinning, the grain boundary topography and grain boundary dislocation (GBD) network structure of [001] tilt YBCO bicrystals were studied by TEM and HRTEM.

Rapidly Solidified Melt-spun Bi-Sn Ribbons: Surface Composition Issues

2016 ◽  
pp. 3287-3297
Author(s):  
Tarek El Ashram ◽  
Ana P. Carapeto ◽  
Ana M. Botelho do Rego
Keyword(s):  
Chemical Composition ◽  
Optical Microscopy ◽  
Melt Spinning ◽  
Surface Composition ◽  
Electrochemical Process ◽  
Melt Spun ◽  
Bismuth Alloy ◽  
The One ◽  
Rapidly Solidified ◽  
Melt Spinning Technique

Tin-bismuth alloy ribbons were produced using melt-spinning technique. The two main surfaces (in contact with the rotating wheel and exposed to the air) were characterized with Optical Microscopy and AFM, revealing that the surface exposed to the air is duller (due to a long-range heterogeneity) than the opposite surface. Also the XPS chemical composition revealed many differences between them both on the corrosion extension and on the total relative amounts of tin and bismuth. For instance, for the specific case of an alloy with a composition Bi-4 wt % Sn, the XPS atomic ratios Sn/Bi are 1.1 and 3.7 for the surface in contact with the rotating wheel and for the one exposed to air, respectively, showing, additionally, that a large segregation of tin at the surface exists (nominal ratio should be 0.073). This segregation was interpreted as the result of the electrochemical process yielding the corrosion products.

An analysis of the transport properties and mechanical stability of rapidly solidified Al-Sb alloy

2015 ◽  
Vol 10 (2) ◽  
pp. 2663-2681
Author(s):  
Rizk El- Sayed ◽  
Mustafa Kamal ◽  
Abu-Bakr El-Bediwi ◽  
Qutaiba Rasheed Solaiman
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Melt Spinning ◽  
Elastic Moduli ◽  
Mechanical Stability ◽  
Microstructural Analysis ◽  
Alloy System ◽  
Antimony Content ◽  
The Stability ◽  
Rapidly Solidified

The structure of a series of AlSb alloys prepared by melt spinning have been studied in the as melt–spun ribbons  as a function of antimony content .The stability  of these structures has  been  related to that of the transport and mechanical properties of the alloy ribbons. Microstructural analysis was performed and it was found that only Al and AlSb phases formed for different composition.  The electrical, thermal and the stability of the mechanical properties are related indirectly through the influence of the antimony content. The results are interpreted in terms of the phase change occurring to alloy system. Electrical resistivity, thermal conductivity, elastic moduli and the values of microhardness are found to be more sensitive than the internal friction to the phase changes. 

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