The Effect of Simultaneous Electron and Kr + Irradiation on Amorphization of CuTi
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THE EFFECT OF SIMULTANEOUS ELECTRON AND Kr+ IRRADIATION ON AMORPHIZATION OF CuTi* J. 1. 2.
Koike
(1,2),
p.
R.
Okamoto
(1),
L.
E.
Rehn
(1),
M. Meshii
(2)
Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 Dept. of Materials Science and Engineering, Northwestern University, Evanston, IL 60208
ABSTRACT CuTi was irradiated with I-MeV electrons and Kr+ ions simultaneously at temperatures from 10 to 423 K. Retardation of Kr+-induced amorphization was observed with simultaneous electron irradiation at 295 and 423 K. The retardation effect increased with increasing irradiation temperature and relative electron-to-Kr dose rate. In contrast, simultaneous irradiation below 100 K showed an additive effect of electron- and Kr+induced amorphization. The results can be explained by the mobility point defects introduced by electron irradiation interacting with Kr+-induced displacement cascades. INTRODUCTION A recent study [1] has shown that amorphization of Si during irradiation with I-MeV Kr+ ions at 10 K can be strongly retarded by simultaneously irradiating the sample with a I-MeV electron beam. The retardation effect under simultaneous irradiation was found to occur only when the calculated electron displacement rate (dpa/s) exceeded that for the Kr+ beam by a factor of about two. Although not yet fully understood, the retarding effect clearly indicates that the primary damage state characteristic of ions which produce dense displacement cascades can be significantly altered by additional Frenkel pair production by electrons. The present paper reports the effect of simultaneous irradiation with I-MeV electrons and I-MeV Kr+ ions on the amorphization behavior of the intermetallic compound, CuTi. which becomes amorphous under Kr+ contrast to Si, In irradiation but not under electron irradiation, CuTi can be rendered completely amorphous by both types of charged particles [2]. As suggested in a recent theoretical study (3] of the amorphization kinetics of intermetallic compounds under simultaneous irradiation conditions, the Kr+-induced crystalline-to-amorphous transition in CuTi can be suppressed or accelerated by simultaneous electron irradiation depending on the irradiation temperature and on the relative dose rate of the electron and ion beams employed. EXPERIMENTAL PROCEDURE The preparation and homogenization treatments of the polycrystalline samples of CuTi have been described previously *The work is supported by DOE W-31-109-ENG-38 and NSF DMR-8411178.
Mat. Res. Soc. Symp. Proc. Vol. 128.
1989 Materials Research Society
340
[4]. Simultaneous irradiations with l-MeV electrons and Kr+ ions were carried out in situ in the Argonne National Laboratory High Voltage Electron Microscope interfaced to a 2-MeV tandem accelerator. Kr+ irradiations were performed using three different current densities of 1.7 x 1010, 5.1 x 1010 and 3.4 x 2 1011 ions/cm /s. The corresponding atomic displacement rates obtained by TRIM calculation [5] using a threshold energy of 21 eV [6] are 5 x 10-5, 1.5 x 10-
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