Effect of heat treatment in atmosphere on mechanical properties of pure titanium at liquid helium temperature

Abstract

Due to their extreme friability, nuclear fusion superconductivity coil materials (NbTi, Nb{sub 3}Sn, Nb{sub 3}Al) are placed in pure titanium rectangular parallelepiped sleeves called conduits, of about 1 mm in wall thickness, and subjected to sintering heat treatment (50 to 200 hours at 923 to 1,023K) to produce superconductive materials. In use, the superconductive coil is immersed in liquid helium (4.2K) and as immense currents flow through the coil, the conduit is subjected to very large electromagnetic forces. As pure titanium is a highly active material, oxided scale forms on the surface when it is heated to high temperatures under atmospheric conditions, together with the formation, beneath the oxided scale, of an oxygen-rich layer possessing intense oxygen solubility. While oxided scale, because of its ability to reduce hydrogen absorption, is being actively used as a means to prevent the hydrogen embrittlement of titanium, it is believed that this leads to a deterioration of the mechanical properties because the oxygen-rich layer is deficient in ductility. The current research is intended to clarify the effect on the tensile test properties at liquid helium temperature (4.2K) of pure titanium and the oxygen-rich layer which forms thereon as a result of the heat treatmentmore » under atmospheric conditions.« less