Young's modulus memory effect during the annealing of submicrocrystalline copper

The temperature dependence of Young's modulus E(T) in submicrocrystalline copper has been investigated both on heating and on cooling within a temperature range from 20 to 400-450degreeC. The copper samples have been subjected to several successive heating-cooling runs with increasing maximum temperature Ta. At T =Ta the samples were annealed for 2h. An initial submicrocrystalline structure with a grain size about 200nm has been produced by heavy plastic deformation. An increase in the modulus during the anneal has been observed. The modulus was measured on rod-shaped samples by a resonance technique at frequencies near 100kHz. Some of the samples exhibit, after the anneals, a splitting of the resonance curve into several maxima. Moreover, the temperature dependences of the additional maxima correspond to the E(T) curves measured during the previous heating-cooling runs. This memory effect is discussed.