The aging of niobium and tantalum tritides: Evolution of hardness in comparison with other properties

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Abstract
Vickers hardness measurements on niobium and tantalum tritides of initial composition NbT0.0225 and TaT0.097, respectively, performed over the first 20 months after T charging, are reported and interpreted. For both tritides, the hardness increases monotonically, but in a decelerating rate, with the 3 He concentration built up upon T transmutation. At given 3 He concentration, the increase per unit 3 He concentration is stronger for Nb than for Ta. To interpret the observed hardness evolution, existing hardening theories are adjusted to the present microstructural situations. It is concluded that the microstructure developing on 3 He precipitation is more disperse in the Nb tritide than in the Ta tritide. These findings are supported by conclusions drawn previously from swelling, acoustic emission, and x-ray diffraction measurements of these materials.