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MM: Metall- und Materialphysik

MM 10: Intermetallic phases

MM 10.5: Vortrag

Montag, 27. März 2006, 17:30–17:45, IFW D

Metastable phase formation in Ti-Al-Nb undercooled melts — •Olga Shuleshova, H-Günther Lindenkreuz, Regina Hermann, Thomas George Woodcock, Wolfgang Löser, and Bernd Büchner — IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany

Metastable phase formation processes in ternary Ti-Al-Nb turbine blade alloys have been studied by containerless electromagnetic levitation for melt undercooling up to 300 K below the liquidus temperature. The recalescence behaviour of Ti₄₅Al₄₅Nb₁₀ indicates β-phase formation with subsequent β to α transformation, whereas from the double-recalescence events of Ti₄₀Al₅₀Nb₁₀, Ti₄₅Al₅₀Nb₅ melts metastable β-phase formation is inferred beyond critical undercooling in the range of 150 K. Dendrite growth velocities of 10 to 20 m/s for highly undercooled Ti-Al-Nb melts are consistent with primary β-phase formation, which is promoted by Nb addition. For Ti₄₅Al₅₀Nb₅ and Ti₄₀Al₅₀Nb₁₀ alloys a second recalescence near 1300^∘C attributed to an α to γ solid state transformation was observed in the pyrometer trace. The γ-phase formation was suppressed in favour of a homogeneous α₂-phase in undercooled Ti₄₅Al₄₅Nb₁₀ samples quenched onto a chill substrate. Whereas, in Ti₄₀Al₅₀Nb₁₀, high undercooling enabled a direct γ-phase solidification.