Effects of simultaneous titanium and tantalum additions on the properties of internal tin type Nb3Sn strands

A series of internal-tin type Nb3Sn sublements which had Nb-7.5wt%Ta filaments and various level of Ti doping were investigated. Titanium was introduced into the Sri core of the subelements such that the core contained 0 at% to 2.8 at% Ti before reaction. A series of pre-reaction and reaction heat treatment were then given to these strands. The Ti and Sri distributions were mapped throughout the strand cross-sections for samples removed at various stages of the heat treatment. The formation rates of Nb3Sn phases containing different levels of Ti were determined. Transport current, upper critical field, and the compositions of the A15 regions were measured for strands doped with various levels of Ti. The influence of simultaneous Ti and Ta doping on the upper critical field as well as high field J(c) optimization was investigated.