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Lecture

Phase equilibria and quenched phases in the Al-rich region of the ternary Al–Mo–Ti system

Thursday (27.09.2018)
12:15 - 12:30 S1/01 - A01
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Materials based on the ternary Al–Mo–Ti system are promising candidates for high-temperature applications. In order to overcome their brittleness at ambient temperature, the positive effect of lamellar structure on the mechanical properties can be utilized. In the present work, the phase equilibria in the Al-rich region of the ternary Al–Mo–Ti system were studied experimentally at 1673 and 1773 K. The high-temperature phases originating from the binary Al–Mo system were successfully quenched and investigated using complementary experimental methods such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), electron-probe microanalysis (EPMA), scanning electron microscopy (SEM) and thermal analysis. It has been demonstrated that the β continuous solid solution and the binary high-temperature AlMo phase are one and the same phase [1, 2]. This is in accordance with the experimental work by Nino et al. [3] and the latest thermodynamic description for the Al–Mo–Ti system performed by Cupid et al. [4]. Moreover, the phase equilibrium studies at 1673 K showed the existence of the newly observed ternary τ phase which crystallizes in a face-centered cubic γ-brass related crystal structure. The crystal structure of τ was investigated by means of XRD, TEM and also determined by single-crystal diffraction analysis from a crystal specimen [2]. The agreement of (i) the atomic ratio transition metal/aluminum of τ and Al63Mo37 from the crystal structure refinement (Al61.6Mo23.7Ti14.7) and the measured chemical composition and (ii) the effect that Ti additions slow down the decomposition kinetics indicates that the τ phase is a ternary extension of Al63Mo37 which is stabilized towards lower temperatures by the substitution of Mo by Ti atoms. Thermal analysis measurements in combination with quenching experiments were conducted to shed light on this fact. Based on the obtained results, isothermal sections at 1673 and 1773 K, the liquidus projection and a partial Scheil reaction scheme were constructed.


[1] M.J. Kriegel et al., Intermetallics 83 (2017) 29

[2] M.J. Kriegel et al., J. Alloys Compd. 706 (2017) 616

[3] R. Nino et al., Intermetallics 11(6) (2003) 611

[4] D.M. Cupid et al., Intermetallics 18(6) (2010) 1185


 

Speaker:
Dr.-Ing. Mario J. Kriegel
TU Bergakademie Freiberg
Additional Authors:
  • Benedikt Distl
    TU Bergakademie Freiberg
  • Prof. Dr. Jens Freudenberger
    Leibniz Institute for Solid State and Materials Research Dresden
  • Dr. Olga Fabrichnaya
    TU Bergakademie Freiberg
  • Prof. Dr. Andreas Leineweber
    TU Bergakademie Freiberg