Influence of defects on thermal and mechanical properties of metals
Kamani, Sandeep Kumar
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The crystallization/freezing and melting phenomena are critical in processing of chemicals and materials. Although melting is a very fundamental problem, the mechanism behind it has not been completely answered satisfactorily. Hence its study becomes very important. Perfect crystals do not exist; therefore it is very important to include the effect of defects in the above mentioned processes. The purpose of this work is to employ molecular simulation to further extend the understanding of theories of melting with respect to defects. We studied the melting and freezing process for a model system of copper with and without defects. We studied point defects (1, 2, 4, 8 vacancies and 1, 2, 4, 8 interstitials), line defects (edge dislocation) and surface defects (grain boundary) using molecular dynamics simulations. Constant stress-constant temperature ensemble with atmospheric pressures is employed. Various properties like average volume, density, potential energy and total energy are obtained as a function of temperature for each system. Most of the properties vary linearly before and after the phase transitions. During the transition process they show a dramatic change. This change is a sign of phase transition. The phase transition temperatures obtained from the single phase simulations are not the true melting (or freezing) points as there is some amount of superheating (or supercooling). Coexistence phase simulations are also done for the case of copper with no defects to find the true melting point. Most of the literature dealing with melting/crystallization on the basis of atomistic simulation does not include the influence of the presence of defects. Thus this work has a bearing on the various theories of melting.