Microstructure and superconductivity in annealed Cu-Nb-(Ti, Zr, Hf) ternary amorphous alloys obtained by liquid quenching

Melt-quenched Cu-Nb-(Ti, Zr, Hf) ternary alloys have been found to be amorphous possessing high strength and good bend ductility. The niobium content in the amorphous alloys was limited to less than 35 at% and the titanium, zirconium or hafnium contents from 25 to 50 at%. The Cu40Nb30(Ti, Hf)30 alloys showed a superconducting transition above the liquid helium temperature (4.2 K) after annealing at appropriate temperatures. The highest transition temperatures attained were 5.6 K for the Cu40Nb30Ti30 alloy annealed for 1 h at 873 K and 8.4 K for the Cu40Nb30Hf30 alloy annealed for 1 h at 1073 K. In addition, these alloys exhibited upper critical magnetic fields of 1.8 to 2.3 x 106 A m-1 at 4.2 K and critical current densities of 2 x 103 to 1 x 104 A cm-2 at zero applied field and 4.2 K. Since the structure of the superconducting samples consisted of ordered phases based on a bcc lattice with a lattice parameter of 0.31 nm, it was concluded that the superconductivity in the Cu40Nb30Ti30 and Cu40Nb30Hf30 alloys was due to the precipitation of the metastable ordered bcc phases. (author)