Modeling of the atomic ordering processes in Fe 3 Al intermetallics by the monte carlo simulation method combined with e
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N ORDERED intermetalics constitute a unique class of materials that form long-range ordered crystal structure below a critical temperature that is generally referred to as the critical order-disorder phase transition temperature, Tc.[1,2] Among these materials, Fe3Al-based intermetallics have been the subject of an increasing amount of studies because they possess attractive properties for the structural applications at elevated temperatures.[3,4] Their excellent oxidation and corrosion resistance, as well as excellent high strength and stiffness, tend to be maintained up to high temperatures due to their tight bonding structure. These promising structural and mechanical properties of the Fe3Albased alloys are attributed mainly to their long-range ordered structure characterized by DO3 superlattice (Figure 1).[5] However, the undergoing continuous transformation from DO3 to B2 ordered structure near 540 °C, unfortunately, results in a dramatic decrease in the mechanical properties,[6] such as the yield strength and stress rupture, thereby limiting the range of engineering usefulness of the alloys. In this respect, the temperature up to which the long-range order (LRO) state can be preserved is of paramount importance for these alloys, so that there are many theoretical and experimental studies on Fe3Al intermetallics, to characterize and modify the transition temperature in order to retain the elevated temperature characteristics.[3,4,6–8] The theoretical studies mainly intend to characterize the ordering behavior of the Fe3Al intermetallics and clarify the effects of temperature and concentration of Al on the ordering process that . AMDULLA O. MEKHRABOV and M. VEDAT AKDENIZ, Professors, are with the Department of Metallurgical and Materials Engineering, Middle East Technical University, 06531 Ankara, Turkey. Contact e-mail: [email protected] Manuscript submitted March 20, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS A
these alloys exhibit. Those features make this alloy suitable particularly for the study of mechanical properties as a function of degree of LRO. The problem of order-disorder phase transitions in solids is a typical many-particle problem that cannot be treated exactly by analytical means. Hence, those problems involving the determination of configuration-dependent characteristics of the systems are successfully tackled by Monte Carlo (MC) simulations, which have wide spread application and become a standard tool for description of different properties of ordered alloys[9,10,11] due to the ease of modeling of equilibrium and nonequilibrium thermodynamic systems by stochastic computer simulation. For investigation of ordering processes in Fe3Al alloys, the cluster variation method (CVM)[12–19] and MC simulation[20–25] have been used extensively. However, it should be noted that the unknown parameters of both CVM and MC simulation methods are the magnitude of ordering energies at the first and second coordination spheres only or their ratios, the values of which are usually taken from the experiment
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