Physical properties of Hastelloy® C-276™ at cryogenic temperatures

In recent years, the Ni-Mo-Cr superalloy Hastelloy (R) C-276 (TM) has been used as a substrate material for fabricating superconducting tapes such as YBCO and MgB2 coated conductors. With increasing piece length, these coated conductors are within reach of large scale commercial applications. However, data on the physical properties of Hastelloy C-276 at temperatures relevant for these applications are not yet available. In this work, physical properties including magnet succeptibility, specific heat, electrical resistivity, and the Seebeck coefficient are measured from 2 to 300 K and thermal conductivity from 2 to 200 K. Our results show that Hastelloy C-276 exhibits Curie paramagnetism between 4 and 300 K with a Curie constant C= 0.091 K. A spin-glass-like behavior is observed below 3 K. The electrical resistivity has a minimum at similar to 12 K, and shows a linear weak T dependence at higher temperatures. The specific heat C-p between 15 and 40 K follows C-p= gamma T +AT(3). Below similar to 10 K, an upturn in C-p/T with decreasing T is interpreted by the existence of very small ferromagnetic clusters. We found relatively strong phonon contribution to the thermal conductivity in the measured temperature range. In addition, we present the thermal diffusivity as a function of temperature calculated from the thermal conductivity and the C-p data. The Seebeck coefficient is found to be proportional to temperature. The results of our measurements provide important data not only for the specific applications of the superconducting coated conductors that use Hastelloy C-276 as substrates, but also for many other potential cryogenic temperature applications. (C) 2008 American Institute of Physics.