Title

A combined first principles and statistical mechanics method for the study of point defects in Al-rich NiAl systems

Date of Completion

January 1999

Keywords

Physics, Condensed Matter

Degree

Ph.D.

Abstract

Ordered intermetallics have emerged as promising candidates for high temperature structural applications. In particular, NiAl alloys have enjoyed a great deal of attention because of their potential to extend operating temperatures in certain applications. The Al-rich phases of the Ni-Al phase diagram have much lower melting temperatures than NiAl and have not received much attention. However, the study of these compounds is important for several reasons. They represent an integral part of the phase diagram and are important to the overall understanding and behavior of the phase diagram. An understanding of their microstructure may provide information that may lead to useful applications. Furthermore, during the micro-alloying of Ni-Al alloys, these phases are often observed to precipitate out. Therefore, we present a detailed study of the Al-rich Ni-Al phases using first-principles pseudopotential calculations in combination with a statistical mechanics method. we study the stable NiAl 3 and Ni2Al3 structures and introduce atomic defects to explore various concentrations about their stoichiometry. We calculate the formation energies and concentrations of the defects to obtain some insight into the microscopic properties of these systems. ^