Phase transformations in the (Ti, Nb)[sub 3]Al section of the Ti-Al-Nb system; 2: Experimental TEM study of microstructures

Journal Article · Fri Jul 01 04:00:00 EDT 1994 · Acta Metallurgica et Materialia; (United States)

DOI:https://doi.org/10.1016/0956-7151(94)90312-3· OSTI ID:7175743

Bendersky, L A; Boettinger, W J ^[1]

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1. NIST, Gaithersburg, MD (United States). Metallurgy Division

In Part 1 of this paper possible transformation paths that involve no long range diffusion and their corresponding microstructural details were predicted for Ti-Al-Nb alloys cooled from the high temperature b.c.c./B2 phase field into close-packed orthorhombic or hexagonal phase fields. In the present paper experimental TEM results show that two of the predicted transformation paths are indeed followed for different alloy compositions. For Ti-25Al-12.5Nb (at.%), the path includes the formation of intermediate hexagonal phases, A3 and D0[sub 19], and subsequent formation of a metastable domain structure of the low-temperature O phase. For alloys close to Ti-25Al-25Nb (at.%), the path involves an intermediate B19 structure and subsequent formation of a translational domain structure of the O phase. The path selection depends on whether B2 order forms in the high temperature cubic phase prior to transformation to the close-packed structure. The paper also analyzes the formation of a two-phase modulated microstructure during long term annealing 700 C. The thermodynamics underlying the path selection and the two-phase formation are also discussed.

• OSTI ID: 7175743
• Journal Information: Acta Metallurgica et Materialia; (United States), Journal Name: Acta Metallurgica et Materialia; (United States) Vol. 42:7; ISSN 0956-7151; ISSN AMATEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOYS
ALUMINIUM ALLOYS
BCC LATTICES
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
CUBIC LATTICES
DATA
ELECTRON MICROSCOPY
EXPERIMENTAL DATA
HCP LATTICES
HEXAGONAL LATTICES
INFORMATION
MICROSCOPY
MICROSTRUCTURE
NIOBIUM ALLOYS
NUMERICAL DATA
ORTHORHOMBIC LATTICES
PHASE TRANSFORMATIONS
THERMODYNAMICS
TITANIUM ALLOYS
TITANIUM BASE ALLOYS
TRANSMISSION ELECTRON MICROSCOPY