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Microstructural stability of fine-grained fully lamellar XD TiAl alloys by step aging

  • Hanliang Zhu
  • K. Maruyama
  • D. Y. Seo
  • P. Au
Article

Abstract

XD TiAl alloys (Ti-45 and 47Al-2Nb-2Mn+0.8 vol pct TiB2) (at. pct) were oil quenched to produce fine-grained fully lamellar (FGFL) structures, and aging treatments at different temperatures for different durations were carried out to stabilize the FGFL structures. Microstructural examinations show that the aging treatments cause phase transformation of α 2 to γ, resulting in stabilization of the lamellar structure, as indicated by a significant decrease in α 2 volume fraction. However, several degradation processes are also introduced. After aging, within lamellar colonies, the α 2 lamellae become finer due to dissolution, whereas most of the γ lamellae coarsen. The dissolution of α 2 involves longitudinal dissolution and lateral dissolution. In addition, at lamellar colony boundaries, lamellar termination migration, nucleation and growth of γ grains, and discontinuous coarsening occur. With the exception of longitudinal dissolution, all the other transformation modes are considered as degradation processes as they result in a reduction in α 2/γ interfaces. Different phase transformation modes are present to varying degrees in the aged FGFL structures, depending on aging conditions and Al content. A multiple step aging reduces the drive force for phase transformation at high temperature by promoting phase transformation via longitudinal dissolution at low temperatures. As a result, this aging procedure effectively stabilizes the lamellar structure and suppresses other degradation processes. Therefore, the multiple step aging is suggested to be an optimal aging condition for stabilizing FGFL XD TiAl alloys.

Keywords

Material Transaction Aging Treatment Lamellar Structure TiAl Alloy Colony Boundary 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© ASM International & TMS-The Minerals, Metals and Materials Society 2005

Authors and Affiliations

  • Hanliang Zhu
    • 1
  • K. Maruyama
    • 1
  • D. Y. Seo
    • 2
  • P. Au
    • 2
  1. 1.Graduate School of Environmental StudiesTohoku UniversitySendaiJapan
  2. 2.Structures, Materials and Propulsion Laboratory, Institute for Aerospace ResearchNational Research Council of CanadaOttawaCanada

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