Second Phase Formation in Aluminum annealed after Ion Implantation with Molybdenum.
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SECOND PHASE FORMATION IN ALUMINUM ANNEALED AFTER ION IMPLANTATION WITH MOLYBDENUM.* 1
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J. BENTLEY, L. D. STEPHENSON,1,2 R. B. BENSON, Jr., P. A. PARRISH, AND J. K. HIRVONEN.4 iMetals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, 2
TN 37830; Department of Materials Engineering, North Carolina State 3 University, Raleigh, NC 27607; Army Research Office, Research Triangle 4 Park, NC; Zymet, Inc., Danvers, MA.
ABSTRACT The microstructure of aluminum annealed after implantation to peak concentrations of approximately 4.4 and 11 at. % Mo was investigated by analytical electron microscopy. AI1 2 Mo precipitates formed with pseudo-lamellar and continuous film microstructures. Video recordings of insitu annealing experiments revealed the details of the phase transformations.
INTRODUCTION The microstructures of aluminum ion-implanted with molybdenum and subjected to various heat treatments are being investigated for correlation with near-surface properties such as corrosion. Previous work by Al-Saffar et al. [1] indicated enhanced corrosion resistance, but dealt chiefly with the as-implanted condition and involved little microstructural characterization. In addition, the Al-Mo binary system is of interest because metastable phase formation was considered to be possible and the equilibrium phase diagram is poorly defined. [2,31 EXPERIMENTAL PROCEDURES Heavily cold-worked aluminum with a purity level of 99.999% was 0 recrystallized by annealing at 350 C for one-half hour. Grain sizes in the range 0.3 to 0.5 mm were produced. Electropolished coupons 38 x 28 x 0.5 mm were implanted with Mo+ ions at the Naval Research Laboratory using dual energy implant schedules. The fluences of 50 and 110 keV ions and the resultant peak concentration of molybdenum (measured by ion backscattering) at the mean projected range of -50 nm are shown in table 1. Disks (3 mm diam) were electrodischarge machined from as-implanted materials. TEM specimens were prepared by backthinning (electropolishing) as-implanted and annealed specimens. Carbon extraction replicas of annealed specimens were also prepared. Post-implantation in-situ annealing was performed in a Philips EM400T/FEG analytical electron microscope with the use of a Philips singletilt heating holder at a pressure of approximately 10-5 Pa (10-7 torr). Conventional vacuum annealing of specimens at a pressure of approximately 10-4 Pa (10-6 torr) was also performed. *Research sponsored by the Division of Materials Sciences, U.S. Department of Energy under contract No. W-7405-eng-26 with Union Carbide Corporation, and by the Army Research Office.
Mat. Res.Soc. Symp. Proc. Vol. 27 (1984) CElsevier Science Publishing Co.,
Inc.
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TABLE I. Fluences of Mo+ ions and peak molybdenum concentrations produced in the specimens for the present study.
50 keV Mo+ ion fluence 2 (ions/m )
110 keV Mo+ ion fluence 2 (ions/m )
Peak concentrationa) (atomic % Mo)
4.88 x 1019
6.14 x 1019
4.4
1.12 x 1020
1.24 x 1020
11.0
a)Measured by ion backscattering. RESULTS AND DISCUSS
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