The Behavior Of Binary Alloys

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Abstract
The behavior of binary alloys was investigated by the Metropolis Monte Carlo Simulations in Matlab. Temperatures, alloy concentrations and interaction parameters are variables being varied in this simulation. Increases in temperature led to an increase in entropy as well as a decrease in relative correlation of orders. The entropy and enthalpy of mixing both were affected by the alloy concentration, with a maximum of 50%. Lastly, the interaction parameter defined the type of bonds that were energetically favorable: for negative bond energies, the alloy consisted of intermetallic compounds whereas for positive bond energies, the two types of atoms had a tendency to cluster and thus phase separation occurred. When the bonding energy
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Although the substitution occurs randomly, an ordered structure can be obtained under certain conditions. For a binary alloy of A and B metals, there are two types of order: long range and short range. The first one measures the fraction of metal A atoms positioned on α sites and the second one is an indicator of the average number of B atoms surrounding an A atom. Depending on the energy of the bonds between the two metal atoms with each other and themselves, an alloy’s ordered state will vary. The extent to which an alloy becomes ordered under certain conditions depends on which arrangement is more energetically favored, given by the state’s Gibbs energy. For low temperatures, the Gibbs energy is proportional to the relative concentrations of the two metals and the bond strengths. Above a critical temperature, the entropy of the solution is dominant and long range order disappears while the short range order is present to a certain extent. [2] This temperature dependence has a significant impact on the applications of a certain material.
The two main methods of studying the order and configuration of alloys are X-rays diffuse scattering and Monte Carlo simulations. The former can be used to study individual “sections” (i.e. short range order) but is extensive as individual experiments on single crystals are needed. In order to study the
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