Identification of precipitate phases in a mechanically alloyed rapidly solidified Al-Fe-Ce alloy
- PDF / 3,328,481 Bytes
- 9 Pages / 594 x 774 pts Page_size
- 14 Downloads / 207 Views
I.
INTRODUCTION
INCREASED demands from aerospace industries for the improved performance of materials have led to the development of a variety of advanced materials for use at elevated temperatures. These developmental efforts have involved processing of materials under far-from-equilibrium conditions, using rapid solidification in the late 1970s and early 1980s and mechanical alloying in more recent years. Additions of transition metals and rare-earth elements to aluminum have resulted in alloys that can be used up to 590 K, competing with the performance of titanium alloys.EqOne such alloy developed by ALCOA in the early 1980s was based on the AI-Fe-Ce ternary system.E21 Strengthening in these alloys is achieved by the transition metal intermetallic compounds. The low solubility and diffusivity of the transition and rare-earth elements result in slow coarsening of these precipitates.t3] The service temperature of these alloys is determined by the transformation of the metastable phases to equilibrium phases and by coarsening of the precipitates at elevated temperatures. Many investigations on rapidly solidified (RS) A1-Fe-Ce alloys have revealed that the strength decreases rapidly at elevated temperatures.t4.5.6] To overcome this deficiency, the RS A1-Fe-Ce alloys were mechanically alloyed to uniformly disperse the thermodynamically stable carbides and oxides in the aluminum matrix; this resulted in increased strength and stiffness at elevated temperatures.17,s] Analytical electron microscopy studies were conducted on both RS and arc-melted buttons of Al-rich A1-Fe-Ce alloys to determine the crystal structure details of the intermediate phases. EgaTable I lists the stable and metastable phases that occur in Al-rich binary A1-Fe and A1-Ce and ternary A1-FeCe alloys and the stable dispersoid phases which form during mechanical alloying.E9-~41A number of studies were conducted
M.L. OVE(~OGLU, Professor, Department of Metallurgical Engineering, Istanbul Technical University, Maslak, Istanbul 80626, Turkey. C. SURYANARAYANA, Professor and Associate Director, Institute for Materials and Advanced Processes, University of Idaho, Moscow, ID 83844-3026. W.D. NIX, Professor, is with the Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305-2205. Manuscript submitted August 4, 1995. METALLURGICALAND MATERIALSTRANSACTIONS A
on the structure and mechanical properties of RS A1-Fe-Ce alloys.t~7~ However, and most surprisingly, there were no detailed studies on the identification of the precipitate/dispersoid phases in the RS plus mechanically alloyed (MA) A1-Fe-Ce alloys. Thus, the objective of the present article is to report on the X-ray diffraction and electron microscopic characterization of the intermetallic phases in an RS and MA A1-8.4 wt pct Fe-3.4 wt pct Ce* alloy. *All compositions in this article are represented in weight percent, unless specified otherwise.
II.
EXPERIMENTAL PROCEDURE
The A1-8.4 pct Fe-3.4 pct Ce alloy used in this investigation was received in the form of RS
Data Loading...
