The dose, temperature, and projectile-mass dependence for irradiation-induced amorphization of CuTi
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M. Meshii Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (Received 28 September 1988; accepted 30 May 1989)
CuTi was irradiated with 1-MeV Ne + , Kr + , and Xe+ in the temperature range from 150 to 563 K. The volume fraction of the amorphous phase produced during room temperature irradiation with Ne + and Kr+ ions was determined as a function of ion dose from measurements of the integrated intensity of the diffuse ring in electron diffraction patterns. The results, analyzed by Gibbons' model, indicate that direct amorphization occurs along a single ion track with Kr + , but the overlapping of three ion tracks is necessary for amorphization with Ne + . The critical temperature for amorphization increases with increasing projectile mass from electron to Ne+ to Kr + . However, the critical temperatures for Kr+ and Xe+ irradiations were found to be identical, and very close to the thermal crystallization temperature of an amorphous zone embedded in the crystalline matrix. Using the present observations, relationships between the amorphization kinetics and the displacement density along the ion track, and between the critical temperature and the stability of the irradiationinduced damage, are discussed.
I. INTRODUCTION An amorphous phase can be formed by various solidstate techniques, such as interdiffusion reactions, ion-beam mixing, ion implantation, mechanical alloying, and hydrogenation. Among these techniques, irradiation-induced amorphization is of special experimental interest because it is one of the simplest and more controllable ways to study the transformation. This is particularly true when the irradiation-induced transformation can be observed in situ with electron microscopy. During the past twenty years a large amount of information on irradiation-induced amorphization has been obtained, particularly in Si,1"4 because of its technological importance. Theories have been developed to explain the temperature5 and projectile-mass dependence of amorphization in Si. 6 ' 7 More recently, it has been found that many intermetallic compounds are also susceptible to irradiation-induced amorphization8"13; however, the effects of temperature and projectile-mass on amorphization of these materials have not been systematically established. In the present work, the dose dependence of amorphization in CuTi irradiated at room temperature with 1MeV Ne + and Kr+ has been investigated and analyzed using Gibbons' model.6 The analysis indicates that amorphization occurs directly in a single ion track with Kr + , but requires three overlapping ion tracks with Ne + . Differences in the displacement density produced by different projectile masses appear to control the amorphization behavior. a) Also
with the Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208.
The temperature dependence of the critical dose for amorphization was also studied with different ions (Ne20, Kr84, Xe131). The results are compared to our previously repor
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