Positron lifetime studies of the hcp to fcc transformation induced by mechanical attrition of elemental titanium

Manna, I. ; Chattopadhyay, P. P. ; Nandi, P. ; Nambissan, P. M. G. (2004) Positron lifetime studies of the hcp to fcc transformation induced by mechanical attrition of elemental titanium Physics Letters A, 328 (2-3). pp. 246-254. ISSN 0375-9601

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S03759...

Related URL: http://dx.doi.org/10.1016/j.physleta.2004.06.029

Abstract

Nanocrystallisation by planetary ball-milling of high purity elemental titanium (Ti) revealed a polymorphic transformation from its normal hexagonal close packed (hcp) structure to a face-centered cubic (fcc) phase. Positron lifetime measurements were carried out on samples collected after different hours of milling to characterize the defect structures at grain surfaces. With increasing hours of milling, the nanocrystalline grain size decreased and the positron lifetimes-one related to the annihilation at the grain surfaces and the other to that at the intergranular open volume domains-increased significantly due to the increased free volume at the trapping vacancy sites. However, between 5 to 10 hours of milling, the two lifetimes decreased before resuming increasing once again. This marked deviation from an otherwise expected continuous increase of positron lifetime coincided with structural rearrangement within the system bringing in an enhancement in the density of electrons. The repacking of atoms along the [0001] crystallographic direction could be a possibility for this observation. Positron radiation effects on the migration and agglomeration of nanoparticles are also discussed.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Titanium; Phase Transition; Nanocrystalline Materials; Positron Annihilation
ID Code:18832
Deposited On:17 Nov 2010 12:19
Last Modified:06 Jun 2011 08:19

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