Hexagonal close packed to face centered cubic polymorphic transformation in nanocrystalline titanium-zirconium system by mechanical alloying

Bera, S. ; Manna, I. (2006) Hexagonal close packed to face centered cubic polymorphic transformation in nanocrystalline titanium-zirconium system by mechanical alloying Journal of Alloys and Compounds, 417 (1-2). pp. 104-108. ISSN 0925-8388

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S09258...

Related URL: http://dx.doi.org/10.1016/j.jallcom.2005.09.035

Abstract

The present study reports a reversible hexagonal close packed (hcp) to face centered cubic (fcc) polymorphic phase transformation in four different nanocrystalline titanium-zirconium binary alloys in the course of mechanical alloying in a planetary ball mill. This transformation is monitored at appropriate stages by X-ray diffraction and high-resolution transmission electron microscopy. Lattice parameter of the nanocrystalline fcc phase is a function of the alloy composition. For a given alloy, the lattice parameter and hence volume per atom increase with increase in milling time under comparable conditions. On the other hand, crystallite size, measured from X-ray peak broadening, significantly decreases with the progress of milling. It is suggested that structural instability due to plastic strain, increasing lattice expansion, and negative (from core to boundary) hydrostatic pressure is responsible for this hcp → fcc polymorphic transformation. The said transformation seems reversible as isothermal annealing at 1000 °C for 1 h or melting the powder mass leads to partial or complete transformation of the milled product from single phase fcc to hcp.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Metals; Nanostructures; Mechanical Alloying; Crystal Structure and Symmetry; X-ray Diffraction
ID Code:18856
Deposited On:17 Nov 2010 12:14
Last Modified:06 Jun 2011 08:15

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