J. Mater. Sci. Technol. ›› 2019, Vol. 35 ›› Issue (11): 2652-2657.DOI: 10.1016/j.jmst.2019.05.061

• Orginal Article • Previous Articles     Next Articles

Solidification pathway and phase transformation behavior in a beta-solidified gamma-TiAl based alloy

Xu H.ab, Li X.B.a*(), Xing W.W.a, Shu L.a, Ma Y.C.a*(), Liu K.a   

  1. aInstitute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
    bMIIT Key Laboratory of Advanced Metallic and Intermetallic Materials Technology, Engineering Research Center of Materials Behavior and Design, Ministry of Education, Nanjing University of Science and Technology, Nanjing 210094, China
  • Received:2018-11-24 Revised:2019-01-24 Accepted:2019-05-15 Online:2019-11-05 Published:2019-10-21
  • Contact: Li X.B.,Ma Y.C.
  • About author:

    1The authors equally contributed to this work.

Abstract:

The phase transformation behavior of an as-cast Ti-42Al-5 Mn (at.%) alloy after subsequent quenching from 1380 °C to 1000 °C was investigated based on the differential thermal analysis (DTA), electron probe micro analyzer-backscattered electrons (EPMA-BSE), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results show that, the solidification path can be summarized as follows: Liquid→Liquid+β→β→β + α→β + α+γ→βo2+γ→βo+γ+α2/γ→βo+γ+α2/γ+βo,sec, with the phase transformation α→β temperature (Tβ) = 1311 °C, phase transformation γ→β temperature of (Tγsolv) = 1231 °C, phase transformation α2→α or βo→β temperature (Tα2→α/Tβo→β) = 1168 °C, eutectoid temperature (Teut) = 1132 °C and Tα2/γ→βo,sec≈1120 °C. In comparison with Ti-42Al alloy, the Teut and Tγsolv are slightly increased while both the Tβ is decreased obviously by 5% Mn addition. When quenched from the temperature of 1380-1260 °C, the martensitic transformation β→α′ could occur to form the needlelike martensite structure in β area. This kind of martensitic structure is much obvious with the increase of temperature from 1260 °C to 1380 °C. When the temperature is below Tγsolv (1231 °C), the γ grains would nucleate directly from the β phase. For the temperature slightly lower than Teut (1132 °C), the dotted βo,sec phases could nucleate in the lamellar colonies besides the γ lamellae precipitated within α2 phase. Finally, at room-temperature (RT), the alloy exhibits (βo2+γ) triple phase with microstructure of βo+lamellae+γ, of which the lamellar structure consists of α2, γ and βo,sec phases. The phase transformation mechanisms in this alloy, involving β→α′, β→γ, α2→α2/γ and α2→βo,sec were discussed.

Key words: Titanium aluminides, Quenching, Phase transformation, Microstructure, β phase