Acoustic emission and deformation bands in Al-2.5% Mg and Cu-30% Zn

摘要: The acoustic emission (AE) generated during Luders and Portevin-Le Chatelier (PLC) deformation bands has been studied in Al-2.5% Mg Cu-30% Zn. It observed that the cumulative AE detected increases at decreasing strain rates while become shorter are increasingly serrated, especially AlMg. Once PLC develop, appears a stepwise fashion. activity concentrates mainly on beginning of every new band, but preceding first load drop. nucleated, propagate with relatively low AE. Some burst is recorded stress raise after drops, continuous type emitted Total rate serrated flow, as regime. increase total correlates very well either shortening or serration amplitude imposed rates. A close correspondence can be established between phenomenology TEM situ HVTEM observations concerning dislocation dynamics breeding localized slip bands. high when (Luders PLC) move smoothly ascribed to multislip mechanism coarse involved movement, which clearly may preclude large bursts. On other hand, relaxation static ageing discontinuous band movement immobilizes previously operative sources, so activation fresh sources necessary order resume deformation. Dislocation movements undeformed systems presumably fast level should possible put into operation. As consequence, At increasing available time for pile up stabilization front drops progressively reduced. Previously now reactivated larger extent, need activation. Reactivation occurs due density planes. In this way per active plane decreases. serrations rationalized same terms. complementary explanation terms crystallographic microbands macro shear nucleation seems case When smooth continuously number unsuccessful needed originate lower than decreases drops. therefore higher ones. Something essentially similar must occur nucleated. No concentrations nor mobile dislocations traverses entire gauge length started by copious (microbands), formed mode reduces step-wise observed.