Preparation Of Nb₃（Al,Ge） Superconductor By Mechanical Alloying

Many scientists believe that Nb3Al will be the ideal choice instead of Nb3Sn for the high field superconducting material of the magnetic confinement fusion reactor in the future.Nb3Al and Nb3Sn both belong to the A15 phase, and have the same crystal structure.Nb3Al has high transition temperature (Tc) 18.9 K, high critical magnetic field (32 T at 4.2 K), and excellen critical current density (1000 A/mm216 T,4.2 K). It is more important that Nb3Al still has good current transmission property under the action of high stress. However the stable phase of Nb3Al can be obtained just about 1800℃ by using the method of equilibrium mutual diffusion.Therefore, the preparation of Nb3Al became very difficult.Mechanical-Alloying(MA) is a method for Nb3Al preparation.Mechanical alloying can not only achieve the purpose of grain refinement, but also effectively control the microstructure, more importantly, also get solid solution in the solid state or to achieve alloyed. Mechanical alloying method will probably achieve Nb3Al at low temperature.In this paper, in order to improve the superconducting properties of the samples,the sintering temperature, environment of sintering are optimized to prepare the superconducting phase of Nb3Al and Nb3(Al,Ge) by MA.A plurality of process parameters sintering temperature, sintering heating rate, sintering environment optimization. When the milling time is too long,Nb2Al and nitride will appear. These impurities will directly affect the superconductivity of the sample. The evolution is (Nb+Al) → Nb(Al)ss+Nb+Al → Nb(Al)ss → amorphous+Nb2N. Improve the sintering temperature can increase the value of Tc and critical current density, but the superconducting transition temperature can only reach 16.1 K. For Nb3(Al1-x, Gex) samples, Ge content of 0.25 sample has a higher Tc, but there are biphasic. Using sintered ceramic boat better than a sealed tube sintering, heating time and heating rate also have a great effect on the superconducting properties of the samples. Though parameter optimization,Tc of Nb3(Al,Ge) can reach almost 18K.