Semester

Fall

Date of Graduation

2002

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Bernard R. Cooper.

Abstract

The addition of transition metal elements can significantly modify physical properties of intermetalic compounds. We studied the influence of Mo and V additives on thermal expansion coefficient (CTE) of Fe3Al and FeAl over the wide range of temperatures. The site preference of both transition metals was determined by FP-LMTO method. Fe3Al in DO3 structure has three non-equivalent lattice sites: FeI site surrounded by eight iron atoms, FeII site with four iron and four aluminum nearest neighbors and Al site. Our calculations show that Fe, site is energetically more favorable for both Mo and V. The obtained site-selection energies of Mo are relatively small, while for V they are much larger indicating that this additive is likely to improve the stability of Fe3Al DO 3 structure. Thermal expansion of pure FeAl and Fe3Al was found directly from FP-LMTO calculations by incorporating them into the Debye model of a solid. The obtained results are within 10% of the experimentally measured values. To test the applicability of the Debye model to these compounds, we performed Molecular Dynamics (MD) simulation based on our many-body atomistic potentials. The potential parameters were fitted to reproduce the total energy of a crystal under various types of deformations obtained by FP-LMTO method and were tested with respect to different structures and vacancy formation energies. For pure iron-aluminides, thermal expansion calculated within the Debye model differs from the results of MD only at high temperatures. However, when the additives are present, the Debye model does not provide the correct description of thermal expansion. Our calculations show that the addition of V decreases the CTEs of both iron-aluminides, while the addition of Mo makes Fe3Al DO3 structure unstable.

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