Alloy design and phase stability of the ternary alloy titanium-aluminum-niobium

摘要

The authors have used high-precision electronic-structure and cluster-variational method (CVM) techniques to study aspects of alloy design involving the phase stability and ordering tendencies of the ternary system Ti-Al-Nb, and the correlation with these to changes in the electronic structure of these materials. This system is of great interest for aerospace applications due to its desirable mechanical properties and low densities. Total energies were computed for 18 binary and ternary bcc superstructures in order to derive parameters for CVM calculations, which showed important strong ordering tendencies in the alloy phase diagram as a function of temperature and alloy concentration. Structural optimization calculations were used to analyze structural instabilities for bcc, fcc, hcp, O-phase, and omega-phase structures. The authors discovered the mechanism for the role of Nb in the structural stability of the O-phase of the ternary intermetallic Ti2AlNb. Calculations were also done to investigate the electronic properties associated with the structural stability of a related class of Laves Phase high-temperature structural materials NbCr2 and HfV2.