On the embrittlement of a rapidly solidified Al-Fe-V-Si alloy after high-Temperature exposure
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I.
INTRODUCTION
IN the last decade, there has been a considerable amount of effort devoted to the development of aluminum alloys with high-temperature stability capable of competing with titanium alloys on a specific strength basis. For application at high temperatures, aluminum alloys should have constituents which do not undergo phase transformation and resist rapid coarsening. The use of such thermally stable dispersoids in aluminum alloys, however, is quite restricted in conventional ingot cast alloys because of the low so!ubilities of thermally stable dispersoid-forming alloying elements in aluminum. The application of rapid solidification processing (RSP) for the development of elevated temperature aluminum alloys has resulted in an emergence of several alloys based on the AI-Fe alloy system, t~-s] Of particular interest are A1-Fe-V-Si alloys which have excellent room-temperature (RT) and hightemperature mechanical properties. I6,7,sl These alloys maintain their strength at higher temperatures than other A1-Fe-X alloys mainly due to the stability of the microstructure at high temperatures. The excellent thermal stability exhibited by these alloys has led to applications involving much higher temperatures than originally conceived for this class of alloys. However, their maximum use temperature at current status is still limited to 350 ~ and thus, the study of these alloys is mostly concentrated on the mechanical behavior at or below 350 ~ Only a few studies have been made on the me-
J.C. LEE, Research Assistant, S. LEE, Assistant Professor, and D.Y. LEE and N.J. KIM, Associate Professors, are with the Department of Materials Science and Engineering and the Center for Advanced Aerospace Materials, Pohang Institute of Science and Technology, Pohang, 790-600 Korea. Manuscript submitted December 7, 1989.
METALLURGICAL TRANSACTIONS A
chanical behavior of these alloys at temperatures above 400 ~ and the results have shown that these alloys are prone to embrittlement after exposure at temperatures above 400 ~176 For the applications of this class of alloys at temperatures close to the maximum use temperature of currently available titanium alloys, it is necessary to build a better understanding of the mechanical behavior at higher temperatures and to identify the critical factors controlling the high-temperature mechanical properties of these alloys. II.
EXPERIMENTAL PROCEDURE
An alloy of the composition AI-8.5Fe-I.3V-1.7Si (wt pct) was received from Allied-Signal, Inc., Morristown, NJ. This alloy is designated as FVS0812 by Allied-Signal, Inc. The alloy was produced by rapid solidification processing/powder metallurgy (RSP/PM) techniques. Melt-spun ribbons (25 to 40/xm thick) were comminuted into - 6 0 mesh powders prior to being vacuum hot-pressed into a 110 mm-diameter billet. This billet was then extruded at 425 ~ into a 19 • 113 mm flat bar. A conventional ingot metallurgy (IM) aluminum alloy, 2219-T8511, currently used for aerospace applications, was also evaluated for comparison purposes. In order to e
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