β Scribed by N. Behnood; J.T. Evans
No coin nor oath required. For personal study only.
Activation analysis has been used to investigate plastic deformation in AI-Li alloys. The flow stress can be resolved into a component produced by work hardening and a friction stress produced by solid-solution or precipitation hardening. Macroscopic work softening is observed at larger strains in impression tests on pr~ipitation hardened specimens and the results of the analysis indicate that softening is caused by a strain-induced reduction in the friction stress. It is believed that work softening results from the shear of ordered precipitates but an argument is presented to show that macroscopic work softening can only occur when Stage III work hardening is established. At higher tem~~tur~, alloys exhibit the Portevin-Le Chatelier (I-LC) effect in both the solution treated and precipitation hardened condition, but, on the basis of the experimental evidence, it is believed that the detailed mechanism responsible is different in precipitation hardened specimens to that which occurs in the classical P-LC effect, and is associated with the shear of ordered precipitates.
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