Microstructure related superconducting and mechanical properties of some Nb-Ti alloys with additions of Ta and Zr

Effect of the substitution of Ta and Zr in different metallurgical states on the micro-structure, lattice structure, superconductivity as well as the mechanical properties like room temperature Vicker´s hardness, tensile strength and ductility of bcc-βTi phase alloys: Nb0.5Ti0.5, Nb0.40Ti0.45Ta0.15and Nb0.40Ti0.45Ta0.075Zr0.075is investigated. Optical, SEM and EDX investigations show the alloys to be of homogeneous bcc-βTi phase with no segregation of Ta or Zr at the grain boundaries upon annealing. The room temperature Vicker´s hardness and tensile strength increase upon addition of Ta and Zr whereas the ductility decreases and these parameters also depend upon the metallurgical of the samples. Among the ternary and quarternary alloys the highest values of Vicker´s hardness: 261 kg/mm²; tensile strength: 694 N/mm²and ductility: 11 are observed for the Nb0.40Ti0.45Ta0.075Zr0.075(1100°C; 30 h). The Tcvalue decreases upon addition of Ta and Zr and also depends on the metallurgical state. The highest Tcand the slope, dHc2/dT|T=Tcvalues are observed for the as cast cold rolled alloys: Nb0.40Ti0.45Ta0.15(Tc= 9.02 K; 2.14 T/K); Nb0.40Ti0.45Ta0.075Zr0.075(Tc= 8.88 K; 4.28 T/K). The critical magnetic field values of Ginzburg-Landau and Maki as well as the Maki parameter are determined which also depend strongly on the metallurgical state. The alloy of composition Nb0.40Ti0.45Ta0.075Zr0.075(as cast; cold rolled) shows the presence of highest spin-orbit scattering for the compensation of paramagnetic limitation.