The superconducting properties of Ti-Nb-Ta ternary alloys were investigated. The upper critical field of Ti-Nb-Ta alloy is about 125kG, which is the highest of known alloy superconductors. Ti-Nb-Ta alloy with fixed Ta content to 5 at % maintains higher transition temperature, it being about 10°K. It has been found that the heat-treatment at 400°C for a long time is optimum for H-Ic characteristic of Ti-25Nb-5Ta alloy, and that this heat-treatment precipitates α-Ti in the matrix. This precipitate was sustained by transmission electron micrograph examination. The magnet wound with Ti-25Nb-5Ta wire produces 60kG without instability and with relatively small current degradation.
With the recent remarkable development of cryogenic appliances data for mechanical properties of various materials at cryogenic temperature have been required. Under these circums tances, our efforts were concentrated to the test method for materials at cryogenic temperature and collecting data on mechanical properties of materials in cryogenic use. In this report, we introduce the test methods and the mechanical properties of materials at temperatures of room to the liquid nitrogen. As for the test methods, we mainly discuss the construction of various cryostats for tensile tests, hardness tests, impact tests and fatigue tests. By using the methods established in this study, we investigated on the mechanical properties of aluminum, copper, 18-8 stainless steel and other metals. Besides these two subjects, we also explain the relation between the martensite transformation in austenitic stainless steels and peculiar behavior of their mechanical properties at cryogenic temperature.