Creep and tensile properties of helium injected Nb--1% Zr

Specimens of commercial purity Nb-1 percent Zr were helium doped by cyclotron α-bombardment near room temperature to gas contents near 2 and 20 at. ppM He, corresponding to helium production in a CTR first wall during approximately one month and one year of operation at 1 MW/m2 neutronic wall loading. These specimens were tensile and creep tested to evaluate the effect of helium, in the absence of other components of CTR radiation effects, on the mechanical properties. Tensile tests at 1000 and 12000C show no significant effect of either helium level on the strength or elongation values. Creep-rupture tests at the same temperatures on Nb-1 percent Zr showed rupture elongations somewhat reduced in the helium injected samples but the dependence on helium content and on test temperature does not fit the usual effect of helium on elevated temperature ductility. It is concluded that in the absence of displacement damage this alloy is resistant to elevated-temperature embrittlement for helium contents up to 20 at. ppM. The resistance to embrittlement results from the precipitation of helium on a submicroscopic level and from the alloy's inherent resistance to grain boundary separation