Structure of grains and grain boundaries in cryo-mechanically processed Ti alloy
- PDF / 873,174 Bytes
- 7 Pages / 595.276 x 790.866 pts Page_size
- 32 Downloads / 155 Views
NANOSTRUCTURED MATERIALS
Structure of grains and grain boundaries in cryo-mechanically processed Ti alloy Arup Dasgupta • S. Murugesan • S. Saroja • M. Vijayalakshmi • M. Luysberg • M. Veron E. Rauch • T. Jayakumar
•
Received: 12 November 2012 / Accepted: 23 January 2013 / Published online: 6 February 2013 Ó Springer Science+Business Media New York 2013
Abstract A Ti5Ta1.8Nb alloy with the major phase as a (hcp) Ti has been subjected to severe plastic deformation by means of cryo-rolling. Significant grain refinement (from *5 lm to *60 nm) has been observed. The mechanism of grain refinement was studied by analysis of lattice strain variations with increase in cold work using XRD technique. Various intermediate stages, such as hardening, alignment of dislocations, cell formation and criticality before new grain formation, were identified. Formation of cells with dislocations alignment at the boundaries and then finally forming an ultra-fine grain structure was confirmed by transmission electron microscopy studies. Detailed grain boundary characterisation has been carried out using high-resolution transmission electron microscopy studies and crystallographic texture analysis. The grain-refined structure was found to possess a large fraction of high angle boundaries identified also as special boundaries by evaluating the misorientation angle/ axis sets for a pair of adjacent grain boundaries.
A. Dasgupta (&) S. Murugesan S. Saroja M. Vijayalakshmi T. Jayakumar Physical Metallurgy Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India e-mail: [email protected] M. Luysberg Ernest Ruska Centre for Microscopy and Spectroscopy with Electrons, 52425 Forschungszentrum Juelich, Germany M. Veron E. Rauch CNRS-Grenoble INP, rue de la Physique, 38402 Saint Martin d’He`res, France
123
Introduction The increasing demand for stronger, more durable and lighter structural materials, has posed interesting challenges to material scientists on innovative methods of synthesis Grain size reduction so as to produce bulk nanostructured materials by severe plastic deformation (SPD) [1], [2] is one such attempt in the right direction. SPD-based synthesis has been carried out by ball milling [3], cold rolling at low temperature [4], high pressure torsion [5], equal channel angular pressing [6], and multiple forging [7]. Amongst these processes, rolling is possibly the simplest method to impart high degree of deformation. A very high degree of deformation can lead to dynamic recovery [8], if carried out at room temperature or above, owing to an increase in temperature during the process. Dynamic recovery phenomenon involves rearrangement of dislocations into dipolar debris and suitable boundary configuration [8]. It is reported in the literature that the rate of dynamic recovery is proportional to the dislocation annihilation frequency [9], which in turn depends on dislocation climb dynamics [10]. It is the dislocation climb mechanism that can be largely suppressed by reducing the concentration of vacancies by
Data Loading...
