Microchemical and microstructural investigations on two-phase intermetallic TiAl/Ti3Al alloys by field ion microscopy and atom probe (APFIM)

Abstract

The microstructure and the chemical compositions of the coexisting TiAl and Al3Ti phases in as-cast Ti–48at%Al and Ti–46at%Al–1at%Cr–0.2at%Si alloys are investigated by field ion microscopy and supported atom probe microanalysis (APFIM). The alloys exhibit a fine-scaled lamellar microstructure. γ-TiAl possesses a high degree of ordering, whereas α2-Ti3Al is off-stoichiometric. The α2/γ interfaces and γ/γtwin twin relations are studied in detail. The true twin boundaries γ/γ in γ-TiAl lamellae are mono-phased, whereas the pseudo-twin boundaries consist of a layered γ/α2/γ structure. Antiphase boundaries (APBs) are present in conventionally cast alloys containing chromium. Additions of Cr decrease the APB energy of TiAl and raise the Al concentration in the Ti3Al phase.