A Study on the Physical Properties of the Newly Calculated Phases of Cu-Al-Be Alloys by ab initio Calculations

C. Soykan Ahi Evran University, Vocational School of Health Services, Kırşehir, Turkey

Received: January 28, 2019; revised version April 17, 2019; in final form July 22, 2019

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Total energy calculations based on density functional theory were performed to investigate the physical properties for the austenitic L21 and newly calculated martensitic phases of the Cu2 AlBe shape memory alloy. When the total energy of all the phases versus the volume data are fitted to the Birch-Murnaghan equation of state, it is seen that the stable martensitic NM, 3M, 5M, and 7M phases of the alloy can exist. The lowest energetic phase was determined as tetragonal non-modulated NM structure. When we compare the energy of the newly calculated martensitic phases to the thermal fluctuation energy barriers (criteria as (3kBT)/2 meV/atom is taken), we are confident that the energy difference between 5M, 7M, and 9R phases and the NM phase is large enough to overcome the thermal energy barrier. Moreover, it has been observed that the calculated elastic constants of austenitic L21 and martensitic NM, 3M, 5M, 7M, and 9R phases provide all the mechanical stability conditions determined according to crystal structure symmetries. We consider that the phases that exceed the thermal energy barriers and satisfy the mechanical stability conditions can exist at a stable energy level. When the partial electronic density of states (pDOS) of the austenitic and martensitic phases are analyzed, it is seen that the most contribution to the electronic density of states comes from Cu t2g and Cu eg states. In addition, it is seen that the contributions to the electronic density of state from not only s, p, t2g and eg states of Al and Be atoms but also s and p states of Cu atom have been observed extremely small quantity in the all austenitic and martensitic phases. On the other hand, the t2g, and eg states of Cu atoms dominate in the electronic nature of the Cu2AlBe shape memory alloy. Cu2AlBe shape memory alloy is a non-magnetic material since all phases of spin-up and spin-down are all symmetrical.

DOI:10.12693/APhysPolA.136.411 topics: shape memory alloys, Cu-Al-Be alloys, structural properties, mechanical properties, electronic band structures.