Elsevier

Journal of Alloys and Compounds

Volume 618, 5 January 2015, Pages 527-532
Journal of Alloys and Compounds

Crystallography and morphology of antiphase boundary-like structure induced by martensitic transformation in Ti–Pd–Fe alloy

https://doi.org/10.1016/j.jallcom.2014.08.258Get rights and content

Highlights

  • The APB-like structure are observed in both 9R and B19 martensite of Ti–Pd–Fe alloy.

  • Atomic displacement on APB-like structure reflects the microdomain by pre-martensite.

  • The density of APB-like contrasts are affected by Fe content in Ti–Pd–Fe alloy.

Abstract

The antiphase boundary (APB)-like structure of both 9R and B19 martensites in the Ti–Pd–Fe alloy was investigated by means of transmission electron microscopy. Some APB-like structures with curved and wide contrasts along the (0 0 1)9R basal plane are observed in 9R martensitic plates. The atomic displacement on the APB-like structure reflects the atomic movement stemming from the microdomains formed as a pre-martensitic transformation. The displacement vector of the APB-like structure in the B19 martensite can be expressed as R = 〈1/3 0 −1/2〉B19. The density of APB-like contrasts increases by the substitution of Fe for Pd in Ti–Pd–Fe alloy.

Introduction

Near equiatomic Ti–Ni and Ti–Pd alloys undergo thermoelastic martensitic transformation from the B2 to B19′ (monoclinic) and B19 (orthorhombic) structures upon cooling, respectively. The former alloy is a technologically important material with superior shape memory effect and superelasticity [1]. The latter alloy is a candidate for high-temperature shape memory material because its transformation temperature is about 800 K [2]. We have discovered an antiphase boundary (APB)-like contrast of the martensite in Ti–Ni and Ti–Pd shape memory alloys so far [3], [4]. We characterized those APB-like structures as a kind of stacking fault with an APB-like morphology that is induced by the martensitic transformation. Recently, Inamura et al. discovered an APB-like contrast in α″ (orthorhombic)-martensite in a Ti–Nb–Al alloy [5]. We also analyzed an APB-like contrast of the B19′ martensite via an R-phase transformation in a Ti–Ni–Fe alloy [6]. It is concluded that the atomic displacement on such contrasts within martensitic variants reflects to the atomic movements stemming from the pre-existing athermal ω-phase and R-phase transformations. All these reports provide the characterization of the APB-like structure in the martensite consisting of simple 2H structures. However, APB-like structure in martensite with long period stacking order (LPSO) structures has not been clarified.

The effect of the substitution of Fe for Pd on the martensitic transformation temperature and structure in Ti–Pd–Fe alloy has been extensively studied [7], [8], [9], [10], [11], [12]. The structures of martensite are dependent on Fe content, they are regarded as LPSO structures with common basal planes, that is, 2H, 9R, 4H and their modified structures with incommensutate periodicities. The aim of the investigation reported here is to clarify the crystallography and morphology of the APB-like structure of the 9R martensite, which is one of the LPSO structures in Ti–Pd–Fe alloy, by means of conventional transmission electron microscopy (CTEM) and high-resolution transmission electron microscopy (HRTEM). Furthermore, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) is applied to analyze the interface structure at the atomic level, by which the relatively heavy atom positions are identified by bright contrast in the image due to atomic number (Z) contrast [13], [14]. The effect of substitution of Fe on the APB-like structure in Ti–Pd–Fe alloy is also discussed on the basis of these observations.

Section snippets

Experimental procedure

Ti50Pd46Fe4 and Ti50Pd43Fe7 alloys were prepared from 99.7% Ti, 99.8% Pd, and 99.5% Fe (mass%) by arc melting in an argon atmosphere. A Ti50Pd50 alloy was also fabricated as a specimen for comparison. The samples were solution treated in an argon atmosphere at 1273 K for 3.6 ks and then quenched in ice water. The transformation temperature to the martensite (Ms) of Ti50Pd46Fe4 and Ti50Pd43Fe7 alloys measured by differential scanning calorimetry were about 690 K and 513 K, respectively, which are in

Results and discussion

Fig. 2a and b shows the typical bright-field image and electron diffraction pattern taken from the area marked B in (a) in Ti50Pd43Fe7 alloy, respectively. The pattern in Fig. 2b consists of reflections along the [0 1 0]9R zone axis, which is a low-index zone axis parallel to the basal plane of martensite with a LPSO structure. We can recognize easily that there is 9R martensite in the area B, since diffraction spots at “1/3” position are seen along the row of 0 0 l* reflections in the pattern, as

Conclusions

An APB-like structure of both 9R martensite in the Ti50Pd43Fe7 alloy and B19 martensite in the Ti50Pd46Fe4 alloy was investigated by means of CTEM, HRTEM and HAADF-STEM. Some APB-like structures with curved and wide contrasts along the (0 0 1)9R basal plane are observed in 9R martensitic plates in the Ti50Pd43Fe7 alloy. The atomic displacement on the APB-like structure reflects the atomic movement stemming from the microdomains formed as a pre-martensitic transformation, in addition to the

Acknowledgments

The authors would like to express their sincere gratitude to Professor Y. Morizono of Kumamoto University for his support in the arc melting and for his valuable comments. The authors are most grateful to Prof. T. Waitz of University of Vienna for arrangements to complete this research.

References (21)

  • K. Otsuka et al.

    Prog. Mater Sci.

    (2005)
  • H.C. Donkersloot et al.

    J. Less-Common Met.

    (1970)
  • M. Matsuda et al.

    Acta Mater.

    (2011)
  • M. Matsuda et al.

    J. Alloys Comp.

    (2014)
  • S. Ii et al.

    Scr. Mater.

    (2002)
  • S.J. Pennycook et al.

    Acta Metall. Mater.

    (1992)
  • M. Matsuda et al.

    Mater. Trans.

    (2008)
  • T. Inamura et al.

    Philos. Mag.

    (2010)
  • K. Enami, Y. Nakagawa, in: Proceedings of ICOMAT-86, Jpn. Inst. Metals, 1986, pp....
  • K. Enami, Y. Nakagawa, in: Proceedings of ICOMAT-92, Monterey Inst. Adv. Studies, 1993, pp....
There are more references available in the full text version of this article.
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