MANY-BODY POTENTIALS FOR CU-TI INTERMETALLIC ALLOYS AND A MOLECULAR-DYNAMICS STUDY OF VITRIFICATION AND AMORPHIZATION

Amorphous materials have no long-range order and thus the computer modeling of their structure and properties requires the use of large blocks containing at least several hundreds of particles. In order to carry out molecular dynamics calculations for blocks of this size it is necessary to employ descriptions of atomic interactions for which such calculations are feasible and which at the same time represent sufficiently accurate models of the systems studied. In this paper we present central force many-body potentials for the Cu Ti system which were constructed so as to reproduce a number of properties of the Cu-Ti, compound (tetragonal structure). We fitted the potentials not only to the available experimental data (equilibrium lattice parameters and enthalpy of mixing) but employed an ab initio method to determine additional data. in particular the bulk modulus. We show here that these potentials ensure the stability of the CuTi2 crystal structure against alternate structures and changes in the c/a ratio and closely reproduce the melting temperature of CuTi2. We then employ these potentials in simulations of the glass transition and amorphization by irradiation and use the concept of atomic level stresses to interpret the results. In the former case we demonstrate that the onset of glass formation occurs at a temperature close to the melting temperature and is characterized by the development of correlations of shear stresses associated with individual atoms; this is similar to previous findings for mono-atomic glasses and it appears to be a general phenomenon. In the latter case we find that in the model amorphization occurs at defect concentrations very close to those observed experimentally and the amorphous state is characterized by a ubiquitous value of the average internal. atomic level shear strain.