Pavilón QUTE, Auditórium – 2. poschodie, FÚ SAV
Fe-Si binary alloy has a variety of applications due to its excellent magnetic and mechanical properties. Some drastic change in mechanical properties as Si concentration increasing to 9-10at.% has been intriguing since a long time ago. To understand the mechanism of the Si concentration dependence of the mechanical properties, especially a degradation of ductility as Si concentration is beyond 9-10at.%, the electronic structure calculations incorporated with phonon vibration effect and thermal electrons excitation are performed to Si-doped bcc-Fe alloy up to 12.5at.%Si, the elastic properties such as bulk modulus, shear modulus and elastic constants have been evaluated using the stress-strain method. The calculations reproduced a non-monotonic change of the elastic properties with Si concentration, found a ductile to brittle transition according to an empirical rule as Si content increases beyond 9.4at.%, which is agree with the well known experimental results. Analysis of density of states, magnetic moment revealed a relation of the elastic properties to the magnetovolume effect of Fe-Si alloy at a low Si concentration up to 8at.%. Further CVM calculation at finite temperature clarified the effect of the D03 ordering on the recovery of elastic properties at Si concentration’s being over 11at.%. Regard the Si concentration of 9-11at.% where the elastic properties decrease sharply, we found that such a degradation is originated from the instability of density of states at the Fermi energy, while this instability is the result of strong repulsive interactions of certain Si-Fe-Si configurations in the Fe-Si alloy. Further calculations with Ni-doping are conducted as considering an attractive feature of Ni in Fe-bcc, which consequently achieved a recovery of all elastic properties. This is an encouraging experience of tailoring the electronic structures by introducing specific atomic configurations which adjusts bonding states and the distribution of electrons toward enhancing specific physical properties.
T. Mohri, Y. Chen, A. Saengdeejing, et al., npj Computational Materials -Nature 3, 10 (2017).
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