Abstract
The effect of solidification parameters such as growth rate V and temperature gradient G_L on microsegregation behaviour of main alloying elements in peritectic Ti-44Al-5Nb-0.2B-0.2C (at.%) alloy was studied. Samples for microsegregation study were prepared by quench during directional solidification (QDS) at various combinations of V and G_L. The studied alloy solidifies with β (Ti-based solid solution with cubic crystal structure) primary solidification phase and undergoes L + β → α peritectic transformation. The energy-dispersive spectrometry (EDS) analyses and calculated effective distribution coefficients k_eff for Al, Ti and Nb confirm that the alloying elements such as Ti and Nb segregate predominantly into the β dendrites and Al into the interdendritic liquid during directional solidification. Formation of the peritectic α-phase (Ti-based solid solution with hexagonal crystal structure) leads to an intensive back-diffusion of the alloying elements. Boron segregates into interdendritic liquid where it forms (Ti,Nb)B particles with ribbon-like morphology. Severity of microsegregation expressed by segregation deviation parameter σ_m^AL for aluminium decreases with increasing growth rate V in the mushy zone and only slightly increases below the mushy zone. Moderate decrease of σ_m^AL with the increase of G_L is observed at all measured positions except the position located close to the dendrite tip.

Key words
titanium aluminides, TiAl, solidification, energy-dispersive spectrometry, microsegregation

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