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We capture the spatiotemporal velocity dynamics of dislocation avalanches inface-centered cubic (FCC) gold and body-centered cubic (BCC) niobium crystalsby compression testing of cylindrical microcrystals. In niobium, avalanchepeak-velocities are over one order of magnitude lower, have distinctly rougheravalanche shapes, and relax more slowly to zero velocity than in gold. Theavalanche dynamics (including averaged avalanche shapes) can be describedreasonably well by mean-field predictions for avalanches near the depinningtransition in the case of gold, but not for niobium. A detailed analysis showsconsistent deviations (non-trivial exponents) from the predicted functionalforms for both gold and niobium if the exponent that describes the velocitydecay of the shape function is treated as a free parameter. While the avalanchesize statistics and related scaling exponents are similar, these noticeabledifferences in the dislocation-avalanche dynamics demonstrate material-specificvariations not predicted by "universal" behavior. The marked difference inavalanche shapes is discussed in terms of edge- and screw-dislocation mobilityof an operating spiral arm source.

Shapes and velocity relaxation of dislocation avalanches in Au and Nb single crystals