Enhanced plasticity and superplasticity of ultrafine-grained nickel


Although superplasticity has intensively been studied for half century, few observations have been reported for pure metals due to fast grain growth at temperatures required for superplasticity. With developing of nanocrystalline materials, there was a hope that superplasticity could be obtained in a number of pure metals. Indeed, low temperature superplasticity in pure nickel was reported in pioneering work in 1999, later superplastic feature of nanonickel was attributed to sulfur presence in grain boundaries. Recently, it was concluded that superplasticity it is not related to the presence of sulfur at grain boundaries or a liquid phase at grain boundaries. Thereby, the phenomenon of superplasticity in pure metals is still far away for our understanding and it requires future work. This report is devoted to reassessment of superplastic behavior of nano-nickel and it provides new results on enhanced plasticity of pure nickel processed by HPT consolidation of rapid quenched ribbons. Bulk ultrafine-grained nickel was successfully processed by RT consolidation of rapid quenched ribbons using high-pressure torsion. RQ nickel possesses equiaxed grain structure with mean grain size of 1−2 μm showing well defined grain boundaries. Upon HPT consolidation mean grain size of ~0.2 μm and high dislocation density have been achieved. However, consolidated Ni specimens show enhanced plasticity >140% at testing temperature of 450°C and strain rate of 10-3 s-1. No superplastic regime has been attained for given testing conditions.

References (16)

R. Z. Valiev, A. P. Zhilyaev, T. G. Langdon. Bulk nanostructured materials: Fundamentals and applications. Wiley & Sons, New Jersey, 2014.
R. Z. Valiev, T. G. Langdon. Principles of equal-channel angular pressing as a processing tool for grain refinement. Prog. Mater. Sci. 51, 881—981 (2006).
A. P. Zhilyaev, T. G. Langdon. Using high-pressure torsion for metals processing: fundamentals and applications. Prog. Mater. Sci. 53, 893—979 (2008).
S. X. McFadden, R. S. Mishra, R. Z. Valiev, A. P. Zhilyaev,A. K. Mukherjee. Low-temperature superplasticity in nanostructured nickel and metal alloys. Nature. 398, 684—686 (1999).
S. X. McFadden, A. P. Zhilyaev, R. S. Mishra, A. K. Mukherjee. Observations of low-temperature superplasticity in electrodeposited ultrafine grained nickel. Mater. Let. 45, 345—349 (2000).
A. P. Zhilyaev. Superplasticity and microstructure evolution in nanonickel. Mater. Phys. Mech. 1,98—102 (2000).
A. P. Zhilyaev, A. I. Pshenichnyuk Superplasticity and grain boundaries in ultrafine-grained materials. Cambridge Intern. Sci. Publ., Cambridge, 2010.
S. X. McFadden, A. K. Mukherjee. Sulfur and superplasticity in electrodeposited ultrafine-grained Ni. Mater. Sci. Eng. A 395, 265—268 (2005).
M. J. N. V. Prasad, A. H. Chokshi. Superplasticity in electrodeposited nanocrystalline nickel. Acta Mater. 58, 5724—5736 (2010).
M. J. N. V. Prasad, A. H. Chokshi. Extraordinary high strain rate superplasticity in electrodeposited nano-nickel and alloys. Scripta Mater. 63, 136—139 (2010).
M. J. N. V. Prasad, A. H. Chokshi. Deformation-induced thermally activated grain growth in nanocrystalline nickel. Scripta Mater. 67, 133—136 (2012).
A. P. Zhilyaev, A. A Gimazov, E. P. Soshnikova, A. Révész, T. G. Langdon. Microstructural characteristics of nickel processed to ultrahigh strains by high-pressure torsion. Mater. Sci. Eng. A 133—136, 207—212 (2008).
K. S. Kumar, S. Suresh, M. F. Chisholm, J. A. Horton, P. Wang. Deformation of electrodeposited nanocrystalline nickel. Acta Mater. 51, 387—405 (2003).
K. S. Kumar, H. Van Swygenhoven, S. Suresh. Mechanical behavior of nanocrystalline metals and alloys. Acta Mater. 51, 5743—5774 (2003) .
N. Wang, Z. Wang, K. T. Aust, U. Erb. Isokinetic analysis of nanocrystalline nickel electrodeposits upon annealing. Acta Mater. 45, 1655—1669 (1997).
H. J. Frost, M. F. Ashby. Deformation-Mechanism Maps, The Plasticity and Creep of Metals and Ceramics. Pergamon Press, Oxford, 1982.