Deformation mechanisms of a rapidly solidified Al-8.8Fe-3.7Ce alloy
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INTRODUCTION
THE promise of Rapid Solidification Processing (RSP) has resulted in a major thrust toward alloy development. Several different compositions and processing techniques are being evaluated by various investigators and the major thrusts have been focused on aluminum and titanium alloys for elevated temperature applications. The evaluation of such alloys has been mostly based on hot tensile tests and very little work has been done on determining the mechanisms of creep of the RSP alloys. Creep resistance is an important attribute of high temperature alloys, and the mechanisms that control creep in the fine-grained RSP alloys must be understood for design of alloys that resist creep. Further, the possible effects of the unique microstructural features of the RSP alloys on their deformation mechanisms make them an interesting material to study. Aluminum based RSP alloys for elevated temperature use have received much attention lately due to their potential as a good lightweight intermediate temperature alloy. Recent research ''~'3 has shown that the A1-Fe-Ce alloys are among the most promising of these alloys. These alloys have grains/cells submicron in size with a large volume fraction of second phase particles. Their microstructures also exhibit good thermal stability, which makes them good for creep studies. In the present work, an A1-8.8Fe-3.7Ce (wt pct) alloy manufactured by hot extrusion of rapidly solidified alloy powders was creep tested in the temperature range of 523 K to 623 K and in the stress range of 20 to 115 MPa, to determine the mechanisms of creep operative in this alloy. II.
EXPERIMENTAL WORK
The material studied was manufactured by hot extrusion at 728 K of rapidly solidified (by atomization) powders of an A1-8.8Fe-3.7Ce (wt pct) alloy. The average powder parD. LEGZDINA, Graduate Research Assistant, and T.A. PARTHASARATHY, Assistant Professor, are with the Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. Manuscript submitted November 10, 1986. METALLURGICAL TRANSACTIONS A
ticle diameter before compaction was 15 /xm (determined on a Fisher subsieve sizer). The composition of the hot extruded alloy is given in Table I. The 0.2 pct yield strength of the alloy was 259 MPa at room temperature and it dropped to 161 MPa at 589 K. 2 The material was supplied in the hot-extruded form by Alcoa/Wright Patterson AFB.
A. Microstructure and Thermal Stability A detailed characterization of the alloy used in this study has been conducted by Angers, Weertman, and Fine.4'5 They used Transmission Electron Microscopy (TEM) to characterize the microstructure of the alloy before and after thermal, thermo-mechanical, and fatigue treatments. They observed little or no coarsening of grains due to thermal or thermo-mechanical treatments. The grains/subgrains were nearly 0.5/xm in diameter, with a very fine dispersion of precipitates. After thermo-mechanical treatments they observed dislocation networks within the grains/subgrains, and some coarseni
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