Time Evolution of Long‐Range Ordering in Fe–Pt Alloys

Abstract

Fe-Pt alloys are a class of materials that have many interesting physical properties. For instance, iron-rich alloys (38-40 at% Pt) have a high corrosion resistance, [1] while platinum-rich alloys (with >80 at% Pt) show high electrical, thermal conductivity, corrosion, and oxidation resistance. [2] In nanostate synthesized Fe-Pt and Fe-Pt-X alloys ordered by L1 0 demonstrate a high coercivity and saturation magnetization at room temperature. [3,4] These properties make Fe-Pt alloys good fit for use in the chemical industry and space technologies.A complex combination of phase transitions is seen in Fe-Pt alloys, as follows: atomic ordering [5] and magnetic ordering [6] with martensitic transformation at lower temperatures for Fe 3 Pt stoichiometry. [7] The interplay between these processes causes different cross effects in their physical properties. Meanwhile, diffusion normally plays the role of control factor.From the structural point of view, Fe-Pt alloys around the 1:3 stoichiometry form Fe 3 Pt or FePt 3 ordered phases with an L1 2type superstructure. At high temperatures, Fe-Pt alloys are disordered with fcc crystal structure in the whole concentration range.An overview of the literature shows that the main techniques to define a long-range order (LRO) parameter in Fe-Pt alloys experimentally are electron diffraction, [8] X-ray scattering, and Mössbauer spectroscopy. [9] The current theoretical approaches are based on the first-principles calculations, [10] and use computational methods such as MD [11] and Monte Carlo. [12] Current research is dedicated to the calculation of the kinetics of the LRO parameter for iron-and platinum-based fcc Fe-Pt alloys. However, the main point here is to have a phenomenological approach with the Önsager-type microscopic diffusion equations to describe atomic ordering and LRO kinetics. Although a similar approach was used in ref. [13] for Ni-based alloys, that study focused on using the CALPHAD computational method.The rest of this article is structured as follows: Section 2 briefly describes the key points of the calculation method for LRO parameter kinetics by means of the diffusion processes, which is then applied to Fe-Pt alloys with different compositions in Section 3. Computational Model2.1.