Consolidation of amorphous copper based powder by equal channel angular extrusion
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Cu50Ti32Zr12Ni5Si1 gas-atomized powder was consolidated by equal channel angular extrusion (ECAE). Powder was vacuum encapsulated in copper cans and extruded at a temperature above the glass transition temperature (Tg), but below the crystallization temperature (Tx). Five samples were subjected to one extrusion pass, each with a different temperature and extrusion rate. Microstructure, thermal stability, X-ray diffraction measurements and hardness of the ECAE consolidates were examined and compared with those of the initial powder and with a conventional extrusion (CE) consolidate. All consolidates exhibit a supercooled liquid region slightly narrower than that of the starting powder. No significant crystallization peaks are observed in XRD measurements; however, changes in peak shape and the total enthalpy of crystallization in differential scanning calorimetry measurements are attributed to nanocrystallization that is not easily detected by these methods. Greater microhardness values in ECAE consolidates in comparison with the starting powder also support the probability of nanocrystallization. The brittle behavior exhibited by all consolidates is attributed to an initial high oxygen contamination of the powder (2000 ppm) and the possibility of crystallization due to long exposure to temperatures above Tg during consolidation. Microstructural examination of the ECAE consolidates shows significant shear deformation of the particles with one ECAE pass. The results of the present study encourage further work on the fabrication of bulk metallic glass from powder by ECAE consolidation. 2003 Elsevier Science B.V. All rights reserved.
