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Segregation and homogenization of a near-gamma titanium aluminide

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Abstract

The nature of microsegregation and the kinetics of homogenization for wrought ingot-metallurgy near-gamma titanium aluminides were investigated experimentally and theoretically. This included heat treatments of the alloy Ti-47Al-2.5Nb-0.3Ta (in atomic percent) in the two-phase (alpha + gamma) and single-phase (alpha) regimes and subsequent electron microprobe analysis to determine the composition of the microstructural constituents. The equivalence of the composition of the gamma constituent in both the single-phase bands and two-phase (alpha-two + gamma) regions of the as-received material and in microstructures developed during subtransus heat treatment revealed that the observed microsegregation is principally morphological in character. Measurements of the kinetics of gamma grain dissolution above the transus temperature, coupled with microprobe measurements of concentration profiles, were used to conclude that the rate-controlling mechanism for homogenization of the near-gamma titanium aluminides is a reaction at alpha-gamma interfaces rather than diffusion-limited dissolution of the gamma constituent. This conclusion was supported by estimates of the interdiffusion coefficient using a spherical-infinite model for gamma-phase dissolution and finite difference calculations of the rate at which concentration gradients in both the alpha and gamma phases would be expected to dampenvia diffusional processes.

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Authors and Affiliations

  1. Metals and Ceramics Division, Materials Directorate, Wright Laboratory, 45433-6533, Wright-Patterson Air Force Base, OH

    S. L. Semiatin (Senior Scientist) & P. A. McQuay (Materials Research Scientist)

Authors
  1. S. L. Semiatin
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  2. P. A. McQuay
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Formerly Senior Research Scientist, Metals and Ceramics Department, Battelle Memorial Institute, Columbus, OH

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Semiatin, S.L., McQuay, P.A. Segregation and homogenization of a near-gamma titanium aluminide. Metall Trans A 23, 149–161 (1992). https://doi.org/10.1007/BF02660861

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  • DOI: https://doi.org/10.1007/BF02660861

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