Amorphisation Tendency of Intermetallic Compounds Under Electron Irradiation
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AMORPHISATION TENDENCY OF INTERMETALLIC COMPOUNDS UNDER ELECTRON D.E. Luzzi and M. Meshii, Department of Materials Science IRRADIATION. and Engineering, Northwestern University, Evanston, IL 60201-9990. ABSTRACT The chemical disordering model for the electron irradiation induced crystalline to amorphous (C-A) transition was previously developed using in-situ experiments in the intermetallic compounds of the Cu-Ti binary alloy system. In the context of this model, a rule was developed which predicts the amorphisation tendency of these and other binary intertransition metal compounds with an accuracy of 92% in the 38 compounds studied to date. Two aspects of this rule, the composition of the compound and the crystal structure are examined through a first approximation computer comparison of ordered, partially ordered, and disordered crystal structures. It is found that in bcc based compounds and in complex crystal structure compounds, the ability of the chemical disordering to raise the energy of the crystal is severely inhibited at compound compositions away from 50:50. During the disordering process, the greatest increase of the crystal energy occurs during the early stages of chemical disordering. These results mesh well with the concept of an amorphous transition driven by the energy increase due to chemical disordering. INTRODUCTION The electron irradiation induced crystalline to amorphous (C-A) transition in intermetallic compounds has become one of the more interesting research subjects in the field of irradiation damage (for a recent review of the early work, see [1]). Most of the work has focussed on the mechanism whereby the energy of the crystal is raised to the point of instability at which the amorphisation results. While it has not yet been rigorously shown what process provides the largest component of the energy increase, several experiments have provided evidence of the importance of the energy increase due to the irradiation induced chemical disordering [2,3]. Recently a rule has been developed to predict the tendency of binary intertransition metal compounds to undergo the C-A transition [4]. This rule states that a compound will amorphise under electron irradiation if 1) both of its constituents are present in concentrations that are equal to or greater than 1/3 (Y>.33) and 2) its constituents are separated in the periodic table by more than 2 groups (&N > 2) and 3) it has a complex crystal structure in the unirradiated state where *d is the concentration of the minor constituent of the compound and &N is the separation of the constituent groups in the periodic table. This rule is composed of three parameters based on properties of the compound and correctly predicts the amorphisation tendencies of the 38 compounds studied to date with an accuracy of >92 %. In the present paper, the effects of two of these parameters, the composition of the compound and its crystal structure, are discussed in relation to their effect on the energy increase of the crystal due to chemical disordering. This is done b
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