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With the objective of achieving high strength and low cost for hot-forged TiAl based alloy containing β phase, the applicability of oxide-crucible-melted ingot was considered for compositions centered on Ti–28.7Al–7.0Mn (wt%). First, as a result of evaluating the influence of crucible contaminants on the hot-forgeability of ingots, it was confirmed that, even at the extremely high oxygen content of 0.35 wt%, hot-forgeability could be maintained if the amount of β phase was recovered at the forging temperature by reducing the Al content. Next, as a result of verifying the industrial practicality of large ingot, it was found that hot-forging under industrially required conditions was indeed possible for an yttria-crucible-melted ingot corresponding to the above-mentioned center composition with an oxygen content of 0.16 wt%; and in terms of machinability and Charpy impact properties of hot-forged and heat treated material, this ingot was superior to triple-melted VAR ingot having an oxygen content of 0.055 wt%, as well as having substantially better creep rupture strength. |
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