Hot isostatic pressing of powder in tube MgB2 wires

Abstract

The critical current density (Jc) of hot isostatic pressed (HIPed) MgB2 wires, measured by d.c. transport and magnetization, is compared with that of similar wires annealed at ambient pressure. The HIPed wires have a higher Jc than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field (Hirr). The HIPed wires are promising for applications, with Jc>106 A/cm2 at 5 K and zero field and >104 A/cm2 at 1.5 T and 26.5 K, and Hirr ~ 17 T at 4 K. The improvement is attributed to a high density of structural defects, which are the likely source of vortex pinning. These defects, observed by transmission electron microscopy, include small angle twisting, tilting, and bending boundaries, resulting in the formation of sub-grains within MgB2 crystallites.Comment: 13 pages,3 figure

Transport properties and exponential n-values of Fe/MgB2 tapes with various MgB2 particle sizes

“…At higher strain the filament was broken. In this case, the degradation of the critical current and n-values confirms the pre-stress model; the behaviour is similar to that of Nb 3 compared with a bulk sample by Dhallé et al [7] and a HIPed wire by A. Serquis et al [8]. …”

“…For the high pressure sintered sample at 35 kbar at 950°C for 0.5 hours, the inductive critical current value was ≈ 10 4 A/cm 2 at 3 T, 20 K. Extrapolation of our measurements at 20 K on tape (b) yields similar values. Moreover, it is also possible to make a comparison with the recent data from Serquis et al [8] who prepared wires by the P.I.T. technique and treated them under hot hisostatic pressure (HIP).…”

Evidence of Point Pinning Centers in Un-Doped Mgb2 Wires at 20 K after HIP Process

“…The decrease of T c of a wire under pressure during reaction would then be related to the loss of p xy holes, the decrease of lattice parameters and of c/a ratio (this effect can create dislocation). On the other hand, Serquis indicated that the annealing in isostatic pressure can increase the density of the MgB 2 material, which also produces small grains, and create dislocations [13]. In another article, Serquis showed that an increase of strain (dislocation) in MgB 2 decreases T c [26].…”

“…Our previous research for doped MgB 2 wires shows that the disadvantages of un-doped MgB 2 can be eliminated by annealing a wire under isostatic pressure (HIP) [10][11][12]. HIP creates dislocations, eliminates voids, produces small grains and small normal area, increases connections between grains, and increases the density and homogeneity of the MgB 2 material [13,14].…”

Carbohydrate doping to enhance electromagnetic properties of MgB2 superconductors

“…Attempts to accomplish this have invoked the introduction of numerous techniques including chemical doping, [2][3][4][5][6] irradiation, 7 and various thermomechanical processing techniques. 8,9 Chemical doping is a simple and readily scalable technique. Since MgB 2 has a relatively large coherence length and small anisotropy, the fluxoids to be pinned are stringlike and amenable to pinning by inclusions and precipitates in the grains.…”