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Metallic Materials Vol. 51 (2013), no. 2, pp.89-99

Title: Effect of solidification parameters on microsegregation behaviour of main alloying elements in a peritectic TiAl based alloy

Abstract: The effect of solidification parameters such as growth rate V and temperature gradient GL 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 GL. 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 keff 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 σmAL for aluminium decreases with increasing growth rate V in the mushy zone and only slightly increases below the mushy zone. Moderate decrease of σmAL with the increase of GL is observed at all measured positions except the position located close to the dendrite tip.

Keywords: titanium aluminides, TiAl, solidification, energy-dispersive spectrometry, microsegregation
Published online: 20-Sep-2017
Year: 2013, Volume: 51, Issue: 2 Page From: 89, Page To: 99
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