Abstract
Recent experiments have shown that nucleation and growth of niobium hydrides at the α/α+β solvus is indicated by the growth of an internal friction maximum ( α-peak). This internal friction maximum has a height proportional to the hydrogen concentration; its position shifts progressively to higher temperatures with increasing hydrogen concentration, and its activation energy is about 0·27 eV. an acoustical loss mechanism which seems to account for this internal friction maximum is discussed in this paper. This mechanism is based upon the thermal generation of kinks on punched-out dislocation; its application to this problem is suggested by two observations. They are: o 1. Punched-out dislocation loops surround the hydride precipitate, and 2. The maximum is characterized by the same activation energy as the α-peak in slightly deformed pure niobium. A semi-quantitative calculation based on this mechanism yields the observed increase in peak magnitude and the temperature shift of the peak with increasing hydrogen concentration. It is shown that a consistent set of dislocation parameters (the density and the loop length) is obtained.
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