Abstract
The solidification behaviour of a number of Ti-Al-Mn alloys has been investigated both experimentally and through CALPHAD methods. The alloys were prepared as 1 kg buttoms by plasma arc melting and had a nominally constant Ti:Al ratio of 1.14 with Mn levels of 5, 10, 20 and 30 at.%. X-ray diffraction showed that the phases γ-TiAl, α2-Ti3Al, β-Ti (Al,Mn) and (Mn,Al)2Ti are present in the alloys in varying quantities following solidification. The 5 and 10% Mn alloys both comprise transformed lamellar dendrites of γ/α2 with interdendritic γ, β and (Mn,Al)2Ti. The quantity of interdendritic material is significantly greater in the 10% Mn alloy. The 30% Mn alloy contains a large volume fraction of primary (Mn,Al)2Ti with only a small amount of γ, β and α2. The 20% Mn alloy has acicular plates of (Mn,Al)2Ti which form a eutectic-like microstructure with the other phases. Melting endotherms, obtained by differential thermal analysis (DTA), for 5 and 10% Mn alloys compare well with CALPHAD calculations. Furthermore the CALPHAD prediction of a eutectic valley between the [β + L] and [(Mn,Al)2Ti + L] phase fields is consistent with both DTA and microstructural observations on all the alloys. © 1997 Acta Metallurgica Inc.
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