Correlation between microstructural evolution during high-pressure torsion and isothermal heat treatment of amorphous Al
- PDF / 852,739 Bytes
- 10 Pages / 584.957 x 782.986 pts Page_size
- 5 Downloads / 288 Views
d Schafler Physics of Nanostructured Materials, Faculty of Physics, University of Vienna, A-1090 Vienna, Austria
Pe´ter J. Szabo´ Department of Materials Science and Engineering, University of Technology and Economy, Budapest, H-1111 Hungary
Ja´nos L. La´ba´r Research Institute for Technical Physics and Material Science, Hungarian Academy of Sciences, Budapest, H-1121 Hungary
Lajos K. Varga Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, Budapest, H-1525 Hungary
Zsolt Kova´cs Department of Materials Physics, Eo¨tvo¨s University, Budapest, H-1518 Hungary (Received 21 December 2009; accepted 23 February 2010)
Al85Gd8Ni5Co2 metallic glass was subjected to partial devitrification by high-pressure torsion, continuous heat treatment, and isothermal annealing. The fully amorphous alloy exhibits a well-defined transition in its first devitrification product during isothermal heat treatments from tm þ a-Al phase mixture to primary a-Al by increasing the annealing temperature above 555 K. This thermal sensitivity predestinates the composition to identify the controversial thermal contribution of the plastic deformation in metallic glasses. Thermal stability and structure of the partially devitrified samples were systematically analyzed and compared by calorimetry, x-ray diffraction, and electron microscopy. It seems that the effect of severe deformation cannot be singled out by a simple isothermal heat treatment; i.e., high-pressure torsion acts as a spectrum of heat treatments performed at different annealing temperatures. I. INTRODUCTION
Amorphous Al-based aluminum–transition-metal– rare-earth alloys (Al–TM–RE) have successfully been synthesized over a wide composition range in the last decades.1 Special compositions of these metallic glasses can produce primary precipitation of a-Al in heat treatments, where the combination of Al nanocrystals and the residual amorphous matrix ensures superior mechanical properties.1,2 The ease of formation of crystalline phase from an amorphous precursor is primarily determined by the nucleation barrier and subsequent kinetics.3 The dominance of a-Al formation in the majority of the Al-based alloys indicates that the combined nucleation and growth process for a-Al formation is the most competitive for a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0164
1388
J. Mater. Res., Vol. 25, No. 7, Jul 2010
nearly all compositions. However, thermodynamic calculations for the Al–Gd–Ni system reveal that the a-Al phase exhibits lower Gibbs free energy than the compound phase; therefore, the low interfacial energy between a-Al embryos and the amorphous matrix is essential in reducing the nucleation barrier.4 The low interfacial energy relies on the fact that the amorphous matrix coordination number is fairly close to that of the face-centered cubic (fcc) structure obtained by atomic structure studies using synchrotron and neutron diffraction.5 After the nucleation of a-Al embryos, the slowly diffusing
Data Loading...
