Conventional and high-resolution transmission electron microscopy (HRTEM) were used to examine the interfacial structures
in a Ti-50Al-5Mo (at. pct) alloy which was processed to produce combinations of γ, B2, and α
2 phases in a single sample. A small amount of a fourth phase labeled ζ was also found in the microstructure. It may be the
phase Ti
2AlN but confirmation requires analysis of the N content in the phase.In this alloy, the orientation relationship between the
γ and B2 phases is {111}
γ ∥}110}
B2 and 〈101]
γ ∥ 〈111〉
B2 with a coherent habit-plane interface parallel to (474)
γ. The orientation relationship between the B2 and α
2 (and also the ζ
@#@) phases is {110}
B2 ∥(0001)
α2/ζ and 〈111〉
B2 ∥〈11-20〉
α2/ζ with a coherent interface parallel to the close-packed planes and along other orientations. The orientation relationship
between the α
2 (and also the ζ
@#@) and γ phases is (0001)
α2/ζ ∥{lll}
γ and (11•20)
α2/ζ ∥<10•1]
γ. The α
2 phase has a coherent interface parallel to the close-packed planes, while the ζ phase appears to adopt the (474)
γ interface plane of the γ phase, similar to the B2 phase. In some cases, the interface configuration between the γ and B2
phases appears to be altered by the presence of α
2 phase, resulting in a semicoherent interface. The phase labeled ζ in this study has the same orientation relationship with
the γ and B2 phases as α
2 but consists of an ABABAC... stacking of close-packed basal planes. The (474)
γ habit plane interface between the γ and B2 phases is analyzed by several different theories of interfacial structure, and
microstructural evolution in this system is also discussed.
Formerly a Postdoctoral Fellow with the University of Wisconsin-Madison, is now with the
This article is based on a presentation made during TMS/ASM Materials Week in the symposium entitled “Atomistic Mechanisms
of Nucleation and Growth in Solids,” organized in honor of H.I. Aaronson’s 70th Anniversary and given October 3–5, 1994, in
Rosemont, Illinois.