Different superplastic deformation behavior of nanocrystalline Ni and ZrO2/Ni nanocomposite

Tensile test and microstructural analysis have been performed on nanocrystalline Ni and ZrO2/Ni nanocomposite produced by pulse electrodeposition, The nanocrystalline Ni is characterized by a mean grain size of 70 nm, and the ZrO2/Ni nanocomposite shows a mean grain size of 45 nm. Both materials reveal a low temperature superplasticity with elongations of 380% and 605% respectively, when deformed at a temperature of 723 K and a strain rate of 1.67 10(-3) s(-1). The ZrO2/Ni nanocomposite also reveals high strain rate superplasticity with an elongation of 400% when the strain rate increases to 1.67 10(-2) s(-1), whereas no large elongation at high strain rate is observed in the nanocrystalline Ni. SEM and TEM were used to examine the microstructures of the deformed samples. The results indicate that fracture is caused by intergrarmlar cracking and cavities form easily in the nanocomposite. A significantly smaller grain size has been measured for the ZrO2/Ni nanocomposite compared to nanocrystalline Ni, which indicates the stable microstructure of nanocomposite. The different superplastic deformation behavior between nanocrystalline Ni and ZrO2/Ni nanocomposite is strongly influenced by the presence of ZrO2 particles. (C) 2007 Elsevier B.V. All fights reserved.