Recovery of Youngs Modulus During Annealing of Submicrocrystalline Cu and Cu : ZrO2 CompositeReport as inadecuate

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Abstract : Young-s modulus of pure Cu 99.98% and precipitate hardened Cu : ZrO2 polycrystals with an ultrafine-grained UFG structure has been investigated at temperatures 20-600°C. Nanoparticles of ZrO2 with a size of about 10nm have been formed by an internal oxidation of Cu-Zr solid solution. The polycrystals have been produced by a heavy plastic deformation using the equichannel angular pressing technique, which yields an average size of grains d of about 200nm. Young-s modulus E has been measured as a function of temperature T and of the annealing temperature Ta. The dependence ETa in Cu-ZrO2 demonstrates a recovery stage near 200-250°C 4-6% increase in E. Structural investigations show that d practically does not change during 2 hours annealing up to 500°C. Such a structural stability was observed only in the composite material. Pure copper with the same type of initial structure d=200nm shows approximately the same recovery in E at T near 200-250°C, however, this recovery corresponds to a steep an order of magnitude increase in d. This fact is a direct experimental proof that the softening of the Young-s modulus in UFG materials is due to not only the smallness of grains but also the structure of grain boundaries and, in particularly, the mobility of grain boundary dislocations.

Author: A. Lebedev Yu. Burenkov S. Pulnev V. Vetrov V. Kopylov



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