Precipitates and fluxoid pinning in a superconducting Nb-Hf alloy

C. C. Koch, Ray Carpenter

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The relationship between superconducting fluxoid pinning and precipitate dispersion was investigated in a high-field type II superconducting alloy. The alloy, Nb·38 at. % Hf, is a b.c.c. solid solution above 1200°C; at lower temperatures the equilibrium structure is two-phase: b.c.c. β and Hf-rich h.c.p. ∞. The quenched alloy was aged at 600°C. The changes in microstructure during ageing were examined by transmission electron microscopy. The attendant changes in superconducting properties—transition temperature (Tc) and critical flux gradient (dB/dr)—were measured by an a.c. susceptibility technique. It was found that precipitation at 600°C proceeds by the formation and growth of strained, partially coherent particles in the b.c.c. matrix termed transition alpha, αt- Particle size measurements indicated that growth of at follows a t1/3 coarsening law after times not longer than ~ 0 5 hr. Transition temperature measurements substantiate this finding. Measurements of dB/dr showed little change from the quenched solution behaviour for short ageing times. This was attributed to the precipitate size being appreciably less than the calculated fluxoid core diameter. At longer times a broad peak in dBjdr developed at a particular value of external field H. Following its initial appearance the peak moved to lower values of H with further particle growth. Comparison of calculated fluxoid spacing at peak field with average particle spacing calculated from measurements on the micrographs indicated a one-to-one correspondence within the experimental limits. An approximate calculation of the point fluxoid pinning force was made from the bulk pinning force and the results are compared to theoretical predictions.

Original languageEnglish (US)
Pages (from-to)303-320
Number of pages18
JournalPhilosophical Magazine
Volume25
Issue number2
DOIs
StatePublished - 1972
Externally publishedYes

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Precipitates
precipitates
Aging of materials
spacing
Coarsening
Temperature measurement
Superconducting transition temperature
alpha particles
temperature measurement
Solid solutions
solid solutions
transition temperature
Particle size
Fluxes
Transmission electron microscopy
magnetic permeability
gradients
Temperature
transmission electron microscopy
microstructure

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Precipitates and fluxoid pinning in a superconducting Nb-Hf alloy. / Koch, C. C.; Carpenter, Ray.

In: Philosophical Magazine, Vol. 25, No. 2, 1972, p. 303-320.

Research output: Contribution to journalArticle

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