Processing effects on the grain-boundary character distribution of the orthorhombic phase in Ti-Al-Nb alloys

Dingqiang Li, C. J. Boehlert

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Abstract

The grain-boundary character distribution of the orthorhombic (O) phase in Ti2AlNb intermetallic alloys was investigated. The alloys were thermomechanically processed either above or below the bcc transus temperature. Using electron backscattered diffraction, the twin-related O-phase variant interfacial planes were identified and quantified. For the subtransus-processed samples, the equiaxed-O/equiaxed-O grain boundaries tended to primarily prefer 65-deg misorientations and secondarily prefer 90-deg boundaries. Of the 65-deg misoriented boundaries, which were preferentially rotated about [001], ∼40 pct contained (110) twin-related interfacial planes. The observations were rationalized by the α2-to-O phase transformation. It is suggested that for subtransus processing within the α 2-containing phase regimes, the resulting heat-treated O + bcc microstructures evolve such that the O/O boundaries tend to exhibit distinct twin-related variants with misorientations between 55 and 65 deg. For a supertransus-processed alloy, it was found that approximately equal distributions of the six resolvable O variants were formed from the dominant parent bcc orientation. The resulting O/O boundaries tended to cluster at near-90-deg misorientations, which can be explained by the bcc/O orientation relationship. It is suggested that whenever the O phase primarily transforms from the bec structure, the resulting O + bcc microstructures evolve such that the O/O boundaries tend to exhibit misorientations near 90 deg.

LanguageEnglish (US)
Pages2569-2584
Number of pages16
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume36
Issue number10
StatePublished - Oct 2005

Profile

Grain boundaries
grain boundaries
misalignment
Processing
Microstructure
Electron diffraction
Intermetallics
Phase transitions
microstructure
phase transformations
intermetallics
electron diffraction
titanium-niobium-aluminum alloy
heat
Temperature
temperature
Hot Temperature

ASJC Scopus subject areas

  • Materials Science(all)
  • Metals and Alloys

Cite this

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abstract = "The grain-boundary character distribution of the orthorhombic (O) phase in Ti2AlNb intermetallic alloys was investigated. The alloys were thermomechanically processed either above or below the bcc transus temperature. Using electron backscattered diffraction, the twin-related O-phase variant interfacial planes were identified and quantified. For the subtransus-processed samples, the equiaxed-O/equiaxed-O grain boundaries tended to primarily prefer 65-deg misorientations and secondarily prefer 90-deg boundaries. Of the 65-deg misoriented boundaries, which were preferentially rotated about [001], ∼40 pct contained (110) twin-related interfacial planes. The observations were rationalized by the α2-to-O phase transformation. It is suggested that for subtransus processing within the α 2-containing phase regimes, the resulting heat-treated O + bcc microstructures evolve such that the O/O boundaries tend to exhibit distinct twin-related variants with misorientations between 55 and 65 deg. For a supertransus-processed alloy, it was found that approximately equal distributions of the six resolvable O variants were formed from the dominant parent bcc orientation. The resulting O/O boundaries tended to cluster at near-90-deg misorientations, which can be explained by the bcc/O orientation relationship. It is suggested that whenever the O phase primarily transforms from the bec structure, the resulting O + bcc microstructures evolve such that the O/O boundaries tend to exhibit misorientations near 90 deg.",
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AB - The grain-boundary character distribution of the orthorhombic (O) phase in Ti2AlNb intermetallic alloys was investigated. The alloys were thermomechanically processed either above or below the bcc transus temperature. Using electron backscattered diffraction, the twin-related O-phase variant interfacial planes were identified and quantified. For the subtransus-processed samples, the equiaxed-O/equiaxed-O grain boundaries tended to primarily prefer 65-deg misorientations and secondarily prefer 90-deg boundaries. Of the 65-deg misoriented boundaries, which were preferentially rotated about [001], ∼40 pct contained (110) twin-related interfacial planes. The observations were rationalized by the α2-to-O phase transformation. It is suggested that for subtransus processing within the α 2-containing phase regimes, the resulting heat-treated O + bcc microstructures evolve such that the O/O boundaries tend to exhibit distinct twin-related variants with misorientations between 55 and 65 deg. For a supertransus-processed alloy, it was found that approximately equal distributions of the six resolvable O variants were formed from the dominant parent bcc orientation. The resulting O/O boundaries tended to cluster at near-90-deg misorientations, which can be explained by the bcc/O orientation relationship. It is suggested that whenever the O phase primarily transforms from the bec structure, the resulting O + bcc microstructures evolve such that the O/O boundaries tend to exhibit misorientations near 90 deg.

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