Structure and stability of a new ternary hexagonal phase in Al3Ti-Based Al-Ti-V alloys

Woong Seong Chang, B. C. Muddle

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Abstract

A novel hexagonal phase (designated H(2)) has been detected as a major constituent of both Al62Ti10V28 and Al55Ti10V35 alloys, following chill casting and after homogenization at 1523 K. The phase H2 has an ordered hexagonal crystal structure (space group P63/mmc, α = 0.558 ± 0.001 and c = 0.450 ± 0.001 nm), similar to that of α2-Ti3Al, and an atomic composition of 54 ± 1 Al - 11 ± 1 Ti - 35 ± 1 V in the chill-cast Al55Ti10V35 alloy. A fine-scale, duplex lamellar structure, developed within the ordered H2 phase in the solid state, was composed of parallel-sided multivariants of ζ-Ti5Al11 phase, formed parallel to (0001)H2. The orientation relationship between constituent phases was of the form (111)ξ ∥ (0001)H2 and <110>ξ ∥ [112̄0]H2. Following homogenization (1 hour at 1523 K) and isothermal heat treatment at temperatures in the range from 1073 and 1273 K, the Al62Ti10V28 and Al55Ti10V35 alloys were observed to develop two-phase microstructures comprising β-(Ti,V)/δ-Al3(Ti,V) and β/ξ-Ti5Al11, respectively. In both alloys, the β phase could be retained as a stable phase to room temperature, regardless of cooling rate, whereas the H2 phase was unstable at temperature below ∼1273 K and was consumed by the formation of ξ phase at lower temperatures.

Original languageEnglish
Pages (from-to)491-501
Number of pages11
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume34 A
Issue number3
DOIs
Publication statusPublished - 1 Jan 2003

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