首页|Microstructure evolution and phase transformation of the mushy zone in a quenched β-solidifying TiAl alloy
Microstructure evolution and phase transformation of the mushy zone in a quenched β-solidifying TiAl alloy
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This study investigates the phase constitutions and transformations that occur in the mushy zone and in the adjacent phase fields of a directionally solidified Ti-44Al-8Nb-1Cr alloy via quenching technique.The results indicate that the mushy zone consists of unmelted β dendrites and interdendritic liquid,whose formation can be attributed to the difference in melting point aroused by local heterogeneity in solutecontent.The β dendrite is composed of numerous subgrains with various orientations.During quenching,the β dendrite transforms into Widmanstätten α via a precipitation reaction,owing to the decreasing cooling rate caused by heat transfer from the surrounding liquid.Additionally,after quenching,the interdendritic liquid is transformed into y plates.Within the single β phase field and the lower part of the mushy zone,a massive transformation of β to γ occurs.Conversely,in the β+α phase field,both β and α phases are retained to ambient temperature.During the heating process,the transformation of α → β gives rise to the formation of β variants,which affects the orientation of β dendrites in the mushy zone.The growth kinematics of the α → β transformation was elucidated,revealing the preferential growth directions of<111>and<112>for β variants.Furthermore,this study presents an illustration of the formation process of the mushy zone and the microstructural evolution during the heating and quenching process.
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