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

The following conclusions have been arrived at as a result of studying the formation mechanism of the oxygen-rich layer which forms, during heat treatment in atmosphere, on pure titanium to be used for conduits of nuclear fusion superconductivity coils and the effect of such oxygen-rich layer on tensile properties at liquid helium temperature. The depth-related distribution of the hardness which forms on pure Ti during heat treatment in atmosphere has been clarified and it has been determined that the distribution of such hardness can be derived by means of an oxygen density distribution formation model in which oxygen diffusion is based on Fick's law. It has been found with regard to the influence of the oxygen-rich layer on fracture ductility of pure Ti at liquid helium temperature that the deeper the oxygen-rich layer, the more marked is the reduction in ductility due to cracks which form preferentially in the oxygen-rich layer.