Long-period ordered superstructures that appear in an (Al,Ga)-rich (Al,Ga)Ti system

Takayoshi Nakano, Koji Hagihara, Satoshi Hata, Hajime Shigyo, Hideharu Nakashima, Yukichi Umakoshi, Ashok Arya, Ulhas D. Kulkarni

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1 Citation (Scopus)

Abstract

Long-period ordered superstructures in an (Al,Ga)-rich (Al,Ga)Ti system composed of (Al,Ga)x Ti100-x (x = 50-65 at. %) were investigated by using melt-spun ribbons, focusing on the ordering process of the superstructural phases. Compositional regions in which h-(Al,Ga)2Ti (Ga2Zr-type), (Al,Ga)5Ti3 and (Al,Ga) 3Ti2 with threefold, fourfold and fivefold periodicity, respectively, appeared coherently in the L10 matrix were identified by electron diffraction patterns in two different temperature conditions of as-spun (a relatively high-temperature state) and heat-treatment at 700°C (a relatively low-temperature state). The (Al,Ga)5Ti3 superstructural phase always existed between the compositional region where h-(Al,Ga)2Ti and (Al,Ga)3Ti2 dominantly appear. Therefore, periodical ordering proceeds following the periodicity of the concentration wave of pure (Al,Ga) layers parallel to {310) in the Ti (002) layers from threefold to fivefold periodicity via fourfold periodicity. We found that the (Al,Ga)3Ti2 long-period superstructural phase preferentially appeared with increasing Ga concentration in the melt-spun ribbon annealed at 700°C. In other words, the h-(Al,Ga)2Ti superstructure with threefold periodicity preferentially appeared at the high temperature and a low Ga concentration. Thus, the (Al,Ga)3Ti 2-type superstructure was never produced without the addition of Ga in the present study. The long-period ordered superstructures were composed of three pairs of primitive cells, (Al,Ga)Ti2, (Al,Ga)Ti3 and (Al,Ga)Ti4, with periodic atomic arrangements corresponding to lean rhombus, fat rhombus and square, respectively. We discuss the ordering process throughout the (Al,Ga)5 superstructure based on the periodic concentration wave and exchange of atoms. The effect of long-period ordered superstructures on hardness is also mentioned.

Original languageEnglish
Pages (from-to)22-37
Number of pages16
JournalPhilosophical Magazine
Volume93
Issue number1-3
DOIs
Publication statusPublished - Jan 1 2013

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics

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