Estimation of the Nb-Ti-Ta phase diagram

The Nb-Ti-Ta ternary alloy system has been studied experimentally using x-ray diffraction, electron microprobe analysis, and measurements of the superconducting critical temperature. This information, together with additional analysis of the thermodynamics of the system, has been used to develop an improved picture of the Nb-Ti and Ta-Ti binary phase diagrams, and the Nb-Ti-Ta ternary phase diagram. The experimental phase diagrams differ in several respects from published versions of the binaries, and the kinetics of the α-Ti precipitation reaction is invoked to explain some of these inconsistencies. The principle differences lie in the position of the (α+β)/β phase boundary in the Nb-Ti binary, which appears to be pushed to higher Nb contents than in the presently accepted phase diagram. An improved ternary phase diagram can be used to suggest alternative alloys and processing to provide high field, high current density Nb-Ti-Ta superconductors for magnet applications