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Title: Part 1: The microstructural evolution in Ti-Al-Nb O + bcc orthorhombic alloys

Abstract

Phase transformations and the resulting microstructural evolution of near-Ti{sub 2}AlNb and Ti-12Al-38Nb O + bcc orthorhombic alloys were investigated. For the near-Ti{sub 2}AlNb alloys, the processing temperatures were below the bcc transus, while, for Ti-12Al-38Nb, the processing temperature was supertransus. Phase evolution studies showed that these alloys contain several constituent phases, namely, bcc, O, and {alpha}{sub 2}; when present, the latter was in small quantities compared to the other phases. The transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray investigations of samples that were solutionized and water quenched were used to estimate the phase fields, and a pseudobinary diagram based on Ti = 50 at. pct was modified. The aging behavior followed three distinct transformation modes, dependent on the solutionizing and aging temperatures. Widmanstaetten formation was observed when a new phase evolved from a parent phase. Thus, Widmanstaetten O phase precipitated within the B2 phase for supertransus fully B2 microstructures, as well as for subtransus {alpha}{sub 2} + B2 microstructures. Similarly, Widmanstaetten B2 phase can form from a fully O microstructure, a transformation that has not been observed before. A third transformation mode involved composition-invariant transformation, where the fully B2 supertransus-solutionized and water-quenched microstructure transformed to a fullymore » O microstructure at 650 C. This microstructure reprecipitated B2 phase out of the O phase with continued aging time. For Ti-12Al-38Nb, Widmanstaetten O precipitation remained the only transformation mode. It is shown that subtransus processing offers flexibility in controlling microstructures through postprocessing heat treatments.« less

Authors:
 [1]; ;  [2];  [3]
  1. Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Mechanical Engineering
  2. UES, Inc., Dayton, OH (United States)
  3. Air Force Research Lab., Wright-Patterson AFB, OH (United States)
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
684450
Resource Type:
Journal Article
Journal Name:
Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science
Additional Journal Information:
Journal Volume: 30; Journal Issue: 9; Other Information: PBD: Sep 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; MICROSTRUCTURE; PHASE STUDIES; TITANIUM BASE ALLOYS; ALUMINIUM ALLOYS; NIOBIUM ALLOYS; INTERMETALLIC COMPOUNDS; HEAT TREATMENTS; CRYSTAL-PHASE TRANSFORMATIONS; MICROSCOPY

Citation Formats

Boehlert, C.J., Majumdar, B.S., Seetharaman, V., and Miracle, D.B. Part 1: The microstructural evolution in Ti-Al-Nb O + bcc orthorhombic alloys. United States: N. p., 1999. Web. doi:10.1007/s11661-999-0240-4.
Boehlert, C.J., Majumdar, B.S., Seetharaman, V., & Miracle, D.B. Part 1: The microstructural evolution in Ti-Al-Nb O + bcc orthorhombic alloys. United States. doi:10.1007/s11661-999-0240-4.
Boehlert, C.J., Majumdar, B.S., Seetharaman, V., and Miracle, D.B. Wed . "Part 1: The microstructural evolution in Ti-Al-Nb O + bcc orthorhombic alloys". United States. doi:10.1007/s11661-999-0240-4.
@article{osti_684450,
title = {Part 1: The microstructural evolution in Ti-Al-Nb O + bcc orthorhombic alloys},
author = {Boehlert, C.J. and Majumdar, B.S. and Seetharaman, V. and Miracle, D.B.},
abstractNote = {Phase transformations and the resulting microstructural evolution of near-Ti{sub 2}AlNb and Ti-12Al-38Nb O + bcc orthorhombic alloys were investigated. For the near-Ti{sub 2}AlNb alloys, the processing temperatures were below the bcc transus, while, for Ti-12Al-38Nb, the processing temperature was supertransus. Phase evolution studies showed that these alloys contain several constituent phases, namely, bcc, O, and {alpha}{sub 2}; when present, the latter was in small quantities compared to the other phases. The transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray investigations of samples that were solutionized and water quenched were used to estimate the phase fields, and a pseudobinary diagram based on Ti = 50 at. pct was modified. The aging behavior followed three distinct transformation modes, dependent on the solutionizing and aging temperatures. Widmanstaetten formation was observed when a new phase evolved from a parent phase. Thus, Widmanstaetten O phase precipitated within the B2 phase for supertransus fully B2 microstructures, as well as for subtransus {alpha}{sub 2} + B2 microstructures. Similarly, Widmanstaetten B2 phase can form from a fully O microstructure, a transformation that has not been observed before. A third transformation mode involved composition-invariant transformation, where the fully B2 supertransus-solutionized and water-quenched microstructure transformed to a fully O microstructure at 650 C. This microstructure reprecipitated B2 phase out of the O phase with continued aging time. For Ti-12Al-38Nb, Widmanstaetten O precipitation remained the only transformation mode. It is shown that subtransus processing offers flexibility in controlling microstructures through postprocessing heat treatments.},
doi = {10.1007/s11661-999-0240-4},
journal = {Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science},
number = 9,
volume = 30,
place = {United States},
year = {1999},
month = {9}
}