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

Pure Nb and Ti have been used as sheath materials for MgB 2 wires examined experimentally. The reason for this research is to compare the effects of these metallic sheaths on the basic properties of MgB 2 superconductor. Single-core SiC doped MgB 2 wires with Nb and/or Ti sheaths have been made by a powder-in-tube in situ process. Different transport currents, phase compositions and grain connectivity were observed for Nb-and Ti sheathed MgB 2 heat treated at temperatures 650-850 • C/30 min. It was found that the critical current density of MgB 2 /Nb annealed above 700 • C rapidly decreases, while J c of MgB 2 /Ti is systematically increasing with temperature. This is explained by the positive role of Ti absorbing impurities from the MgB 2 core and by the negative effect of boron diffusion into Nb, reducing the quantity and worsening the quality of the MgB 2 core. The obtained results show clearly that a Ti sheath offers the application of higher heat treatment temperatures (above 700 • C) and consequently the achievement of higher critical current densities in comparison to MgB 2 /Nb.

Section: Critical Current Densitiesmentioning

confidence: 97%

Section: Critical Current Densitiesmentioning

confidence: 99%

Properties ofin situmade MgB₂in Nb or Ti sheath

Kòváč¹,

Hušek²,

Kopera³

et al. 2012

“…However, this effect is not sufficient to explain the presented difference in J c . It has already been shown that the Ti-barrier absorbs impurities from MgB 2 filaments during the final HT, which has a beneficial effect on J c , especially for T HT > 750 • C [3,14]. Instead of this, coefficients of thermal contraction (CTC) for Ti-and Nb-barriers are different.…”

Section: Methodsmentioning

confidence: 99%

Selected properties of GlidCop^®sheathed MgB₂wires

Kòváč

Melíšek

Kopera

et al. 2012

GlidCop® sheathed MgB2 wires containing 1–30 filaments have been manufactured by a powder-in-tube process. Two materials (Nb or Ti) have been used for barriers protecting the filaments against the diffusion of copper. Different deformations (drawing, rolling, rotary swaging and isostatic pressing) have been applied to the 30-filament wires prior to the final heat treatment. Critical current densities, Jc, were measured at low external magnetic fields including the self-field and at temperatures from 4.2 to 20 K by a short pulse currents. This allows a detailed pinning force analysis to be made, which has not been done up to now from the transport current data. The resistance of 1–30 filament wires against axial tensile stress has also been examined at 4.2 K. It was found that filament density influences not only the transport Jc but also the resistance to tension stress. While an increased filament density improves Jc the opposite effect has been found for resistance to axial tension. AC losses measured by a calibration-free technique of non-twisted wires have shown the dominant effect of the filament architecture and critical current densities.

“…Theoretical models which permit the calculation of such a complex problem are very complicated and are not broadly available. Therefore, a simplified empirical form for calculation of the effective diffusion coefficient D eff was used and the results were compared through a combination of optical and SEM micrographs, EDX analysis and microhardness measurements [11,12]. It should be noted that D eff calculations are limited by the geometry and composition of the composite wire and heat treatment conditions.…”

Section: Ti-cu Interfaces (The P2 Zone)mentioning

confidence: 99%

Calculated and measured normal state resistivity of 19-filament MgB₂/Ti/Cu/stainless steel wire

Kopera¹,

Kòváč²,

Hušek³

2012

This work describes the resistivity evolution of filamentary MgB 2 /Ti/Cu/stainless steel wire under the influence of solid state interaction between individual elements of the composite. The experimental samples were heat treated at temperatures of 650-850 • C and the properties of the interface layers have been estimated on the basis of solid state growth of intermetallic compounds formed by diffusion. The corresponding composite resistivity along the longitudinal direction was calculated using a model represented by an equivalent parallel circuit of n resistors. The temperature dependence of the electrical resistivity was measured for the experimental sample, a specially prepared Cu/Ti couple, and all individual metallic components used in the sample, using a cryogen-free characterization system. Very good agreement between the calculated ρ(T) dependences and the experimentally measured resistivity of 19-filament MgB 2 /Ti/Cu/stainless steel wire has been obtained.