Effect of cold isostatic pressing on the transport current of filamentary MgB₂wire made by the IMD process

Abstract

This work describes the effect of cold isostatic pressing applied to as-drawn filamentary wires in a GlidCop and/or Cu sheath made by the internal magnesium diffusion process. Critical currents of as-drawn and isostatically pressed wires at high pressures up to 2.0 GPa followed by heat treatment at 640 °C for 40 min were measured. The obtained results show an improvement in boron powder density resulting in an increase of the critical current of MgB2 layers. The engineering current density increases by 4–13 times after the high-pressure treatment, and is influenced by the density of the boron powder and by the mechanical strength of the outer sheath.

Multi-core MgB2 wire with a Ti barrier and a reinforced Al+Al2O3 sheath

“…For the present six-core wire exposed to cold isostatic pressing up to 2 GPa, the R(T) characteristics have shown only a slight, but systematic, decrease in T c with applied pressure (from 36.8 to 36.6 K in the rolled wire, and from 36.1 to 35.7 K in the drawn one). We observed a similar effect for the GlidCop sheathed multicore wire subjected to the same pressures, where T c =36.8 K of unpressed wire was reduced to 36.2 K (by 0.6 K) after 2 GPa isostatic pressing [15]. The T c decrease by applied isostatic pressure is attributed to a residual strain acting on MgB 2 formation, where the residual strain increases with the degree of applied pressure.…”

“…While cold pressing with p=2 GPa improved the J e of as-drawn wire with an Al+Al 2 O 3 sheath by 3.38 times, only a 1.55 times J e improvement was reached for the more dense as-rolled wire densified by the same pressure. The presented results are compared with similar experiments done for multi-core IMD wires in figure 6, where the ratios J e(2GPa) /J e(0) =11.4 and 4.17 have been obtained for Cu and GlidCop outer sheaths, respectively [15].…”

“…Because the density of boron powder prior to the final heat treatment is a decisive factor for high critical current densities, the effect of densification by cold isostatic pressing was verified for the present MgB 2 /Ti/Al+Al 2 O 3 wire. Figure 6 shows the evolution of J e with the pressure applied for rolled and drawn six-core wires, compared with similarly pressed GlidCop and Cu sheathed wires [15]. It is evident that J e of all wires can be improved by the boron densification, and J e is affected by the applied deformation and also by the sheath material used.…”

Fast creation of dense MgB2phase in wires made by IMD process

“…There are several factors that may control the formation rate of the MgB 2 layer: (i) annealing parameters (temperature/ time) [7], (ii) morphology of the B powder [9] (iii) thickness of the B layer [10] and also (iv) density of the B layer prior to MgB 2 phase formation [11]. Usually, MgB 2 wires made by IMD process are finally heat treated at temperatures close to the melting point of magnesium for one or several hours [7][8][9][10][11].…”

Effect of Rapidly Annealing Process on MgB2 Superconducting Wires

“…In-situ MgB2 in the fabrication of superconductor wires has preferred due to the benefit as possible heat treatment at low temperature, comfortable doping, control of particle size, and high critical current density under applied external magnetic field [21]. Additionally, there are various parameters that may control and affect the formation rate of the MgB2 layer as annealing temperature and time [22], cooling and heating rate [23,24], morphology of the B powder [25] thickness of the B layer [26] and also density of the B layer [27]. The factors affecting Jc performance are weak inter-grain connectivity, porosity, and low MgB2 core density [28,29].…”