Effects of Be Additions on Microstructures of TiAl Intermetallic Compounds

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  • Nonaka Katsuhiko
    Department of Materials Science and Technology, Faculty of Engineering, Iwate University
  • Kawabata Takeshi
    ATOM Materials Research Laboratory
  • Nakajima Hideo
    The Institute of Scientific and Industrial Research, Osaka University
  • Tanosaki Kazuo
    Department of Materials Science and Technology, Faculty of Engineering, Iwate University

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  • Effects of Be Additions on Microstructu

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Abstract

TiAl-0.1–3.0 mol%Be alloys made by the argon arc melting method were investigated to characterize microstructures in cast and annealed conditions using optical microscopy, SEM, EPMA and X-ray diffractometer. The addition of Be to TiAl resulted in a decrease of α2 phase, thereby coarsening grains and a shift of γ⁄(γ+α2) phase boundary to Ti-rich side. Two types of Be compound were observed: one was a few micron size of particles which contain a large amount of oxygen and the other was a coarse and eutectic-like phase (θ) which has an atomic ratio of Ti:Al:Be=41:30:29. The solubility limit of Be in TiAl was less than 0.1 mol%. In the (γ+θ) two phase and (γ+α2+θ) three phase regions, an increase of Be addition beyond the solubility limit resulted in a small increase of Ti/Al compositional ratio in γ phase. A volume fraction of lamellar structure in TiAl–Be ternary alloys was smaller in the cast structure but was larger in the annealed structure than that in TiAl binary alloys which have nearly the same Ti/Al ratio as that in the ternary alloys, because the Be addition may increase the stacking fault energy and will stabilize the lamellar twin boundaries, respectively.

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