Temperature-dependent impact of antiphase boundaries on properties of Fe3Al

Abstract

We have performed a quantum-mechanical study of the influence of antiphase boundaries (APBs) on the temperature dependence of selected materials properties of Fe3Al. We show that the studied APBs very strongly affect thermal vibrations of Fe3Al and reduce the width of the band gap in phonon frequencies. Our results also show that the Fe3Al with APBs exhibits higher volumetric thermal expansion than the defect-free Fe3Al. The computed free energy of APBs is found to be strongly temperature-dependent. It is lower than the static-lattice temperature-independent APB energy and the reduction is enhanced by increasing temperature (to 76% at T = 700 K). We have also addressed the discrepancy between the experimental bulk modulus and previous theoretical results obtained for the defect-free Fe3Al. Due to the presence of APBs, the bulk modulus is reduced from the value of 173 GPa, that corresponds to the defect-free Fe3Al, to 153 GPa, i.e. very close to the experimental value of 147 GPa (at T = 0 K). Our study illustrates the impact of extended defects on the elastic properties of Fe3Al and indicates that the studied APBs elastically soften Fe3Al.