摘要
The phase transformation behavior of an as-cast Ti-42Al-5 Mn(at.%)alloy after subsequent quenching from 1380℃to 1000℃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→βo+α2+γ→βo+γ+α2/γ→βo+γ+α2/γ+βo,sec,with the phase transformationα→βtemperature(Tβ)=1311℃,phase transformationγ→βtemperature of(Tγsolv)=1231℃,phase transformationα2→αorβo→βtemperature(Tα2→α/Tβo→β)=1168 C,eutectoid temperature(Teut)=1132℃and T(α2/γ→βo,sec)≈1120℃.In comparison with Ti-42 Al alloy,the Teut and Tγsolv are slightly increased while both the Tp is decreased obviously by 5%Mn addition.When quenched from the temperature of 1380-1260℃,the martensitic transformationβ→α'could occur to form the needlelike martensite structure inβarea.This kind of martensitic structure is much obvious with the increase of temperature from 1260℃to 1380℃.When the temperature is below Tγsolv(1231℃),theγgrains would nucleate directly from theβphase.For the temperature slightly lower than T(eut)(1132℃),the dottedβ(o,sec)phases could nucleate in the lamellar colonies besides theγlamellae precipitated withinα2 phase.Finally,at room-temperature(RT),the alloy exhibits(po+α2+γ)triple phase with microstructure ofβo+lamellae+γ,of which the lamellar structure consists ofα2,γandβo,sec phases.The phase transformation mechanisms in this alloy,involvingβ→α',β→γ,α2→α2/γandα2→βo,sec were discussed.
The phase transformation behavior of an as-cast Ti-42Al-5 Mn（at.%） alloy after subsequent quenching from 1380 ℃ to 1000 ℃ 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→βo+α2+γ→βo+γ+α2/γ→βo+γ+α2/γ+βo,sec,with the phase transformation α→β temperature（Tβ）=1311℃,phase transformation γ→β temperature of(Tγsolv)=1231℃,phase transformation α2→α or βo→β temperature(Tα2→α/Tβo→β)=1168 C,eutectoid temperature(Teut)=1132 ℃ and Tα2/γ→βo,sec≈1 120℃.In comparison with Ti-42 Al alloy,the Teut and Tγsolvare slightly increased while both the Tp is decreased obviously by 5% Mn addition.When quenched from the temperature of 1380-1260 ℃,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℃ to 1380 ℃.When the temperature is below Tγsolv（1231℃）,the γ grains would nucleate directly from the β phase.For the temperature slightly lower than Teut（1132℃）,the dotted βo,sec phases could nucleate in the lamellar colonies besides the γ lamellae precipitated withinα2 phase.Finally,at room-temperature（RT）,the alloy exhibits（po+α2+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.
