Collision Cascades in Zr 3 Al
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COLLISION CASCADES IN Zr 3 Al
L.M. HOWE AND M.H. RAINVILLE AECL Research, Advanced Materials Research Branch Chalk River Laboratories Chalk River, Ontario KOJ IJO Canada ABSTRACT Zr 3 Al is an ordered f.c.c. alloy of the Li 2 type, which under various irradiation conditions can be disordered and then eventually amorphized. In the present transmission-electron-microscopy (TEN) investigation, the nature of the damaged regions formed in individual collision cascades was investigated using 6 low fluence (- 1 x 1011 Ions cm- 2 ) bombardments at 290 K 3 with 15 - 120 keV Cu ions. Imaging under dynamical conditions with the fundamental 111, 200, 220 and 113 reflections revealed damaged regions (5.1 - 8.1 nm average diameter) that exhibited black-white strain contrast features. These damaged regions have essentially a spherically symmetrical strain field and probably are three-dimensional clusters of point defects. Imaging with 110 superlattice reflections revealed additional damaged regions (2.4 - 3.7 nm average diameter), which appeared as black spots, that represent disordered regions in the ordered lattice. For both the strain-contrast regions and the disordered regions, as the incident ion energy increased, the number of damaged regions produced per incident ion increased and the fraction of the theoretical collision cascade volume occupied by these regions decreased. INTRODUCTION The present investigation is part of a research program aimed at better understanding the processes that control irradiation-induced phase changes and solute segregation in zirconium alloys. In our previous TEM investigations [1-4], it was observed that during bombardment with high energy (0.5 - 2.0 NeV) 4 0 Ar and 1 4 N ions there was an irradiation-induced transformation from the ordered - disordered - amorphous states with increasing ion fluence. Subsequent investigations using other heavy ions [5] as well as electrons [4-6] have confirmed the above phase transformations. Various theories have been proposed to explain the irradiation-induced transformations in Zr 3 Al, as well as in other intermetallic alloys [1,5,7,8]. More detailed information about the nature of the damage in individual cascades should help improve our understanding of irradiation-induced phase changes. Irradiation-damage investigations on ordered alloys provide information about defects resulting from displacement collisions as well as disordered regions resulting from replacement collisions. Some examples of previous studies of collision cascades in ordered alloys can be found in ref.[2, 9-11]. In this investigation, low-energy heavy-ion bombardments were used to observe the details of the irradiation damage produced within individual collision cascades in Zr 3 Al.
Mat. Res. Soc. Symp. Proc. Vol. 201. c 1991 Materials Research Society
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EXPERIMENTAL DETAILS AND ANALYSIS Electropolished discs of ordered Zr 3 Al were implanted at 290 K with Cu ions at energies of 15, 30, 45, 60, 80, 100 and 120 keV to fluences of 9.3 x 1010, 1.2 x 1011, 8.7 x 1010, 1.4 x 1011, 9
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