The influence of HIP process on critical parameters of MgB2/Fe wires with big boron grains and without barriers

We show transport results of the critical temperature (Tc), irreversible magnetic field (Birr), upper critical field (Bc2), critical current density (Jc) and the pinning force (Fp) for undoped MgB2 wires without barriers. The results of SEM show that the hot isostatic pressure process increases the density and uniformity of MgB2 materials. Hot isostatic pressure allows for obtaining small grains and increasing the number of connections between the grains, accelerated reaction rate and limits the diffusion of Fe atoms into MgB2 material from the adjacent sheath. The pressure of 1.1 GPa increases Tc quite significantly in high magnetic field range of 6-12 T, improves the Birr and Bc2 and increase the Jc at 4.2 K and 20 K of about three times. Our results may be important for this field since many MgB2 wires are made from big grains of boron greater than 1 μm. Moreover, our research can be important for the production of MgB2 wires for the International Thermonuclear Experimental Reactor with boron 11B.