Compositional Effects on Processing and Properties of Nickel Aluminides
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COMPOSITIONAL EFFECTS ON PROCESSING AND PROPERTIES OF NICKEL ALUMINIDES* VINOD K. SIKKA Metals and Ceramics Division, Building 4508, Oak Ridge National Laboratory, P. 0. Box 2008, Oak Ridge, TN 37831-6083 ABSTRACT Compositional effects on hot and cold workability of ductile-ordered nickel aluminides are described. Compositional effects studied include variations of chromium, aluminum, iron, and zirconium. The hot and cold workability of various nickel-aluminide alloys was ranked with respect to workability of stainless steel. The nickel-aluminide alloy containing chromium and low zirconium (IC-218LZr) had the best combination of hot and cold workability. This alloy also offered a good combination of strength and ductility values over a range of test temperatures. INTRODUCTION Nickel-aluminide intermetallics based on ductile NiaAl containing boron are becoming useful structural materials because of their several unique properties [ 1-3]. These materials are sufficiently different from conventional materials, therefore, their commercial use will require the development of processing technology and properties data. The purpose of this paper is to describe the current status of this development. HOT WORKABILITY Cylindrical specimens of 25-mm diam and 50-mm length were prepared from cast ingots of various alloys (see Table I for alloy compositions). These cylinders were heated at various temperatures in the range of 950 to l20WC and compressed in 25% reduction steps. After each 25% reduction, specimens were cooled and observed for any defects. If no defects were observed, specimens were reheated and compressed an additional 25%. Similar steps were repeated until a total reduction of 75% or failure of the specimen. Data from these tests were plotted as deformation maps. Data points showing no defects or minor defects were connected to show the region of hot workability. The deformation map for IC-218 containing low and high zirconium levels are compared in Fig. 1(a) and 1(b). A similar deformation map for IC-357 containing iron is shown in Fig. 2. The following observations are possible from these figures.
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Low zirconium nickel aluminide containing chromium (IC-218LZr) is more hot workable than the corresponding high zirconium (IC-218) alloy.
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Nickel aluminide containing chromium and iron (IC-357) is significantly more hot workable than nickel aluminide containing chromium and low zirconium (IC-218LZr).
Deformation maps presented above have been successfully utilized for hot processing of IC-218LZr and IC-357 ingots into round bar, sheet bar, sheet, and tube blanks. A hot extruded tube blank of IC-357 is shown in Fig. 3.
*Research sponsored by the U.S. Department of Energy, AR&TD Fossil Energy Materials Program under contract DE-ACO5-84OR21400 with Martin Marietta Energy Systems, Inc.
Mat. Res. Soc. Symp. Proc. Vol. 133. 01989Materials Research Society
488
Table I. Chemical compositions of nickel aluminides investigated
Weight (%) Element
At Cr Fe Zr Mo B Ni
IC-50
IC-218a
IC-221
11.3
8.5 7.8
8.5 7.8
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