The Workability of "XD" Titanium Aluminide Alloys With Low Volume Fractions of TiB2

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Titanium aluminides are being considered as possible replacements for superalloys in some aerospace structural and engine applications [1,2]. However, the low temperature brittleness of these alloys and their high temperature strength, makes them difficult to process. The addition of titanium diboride particles to titanium aluminides has been shown to improve their high temperature workability. Current practice in this field usually involves adding 7.5 vol% titanium diboride to these alloys [1]. This volume fraction of TiB2 was believed to maximize the strength of the alloy, but was found to have little effect on the strength. The most visible effect of the titanium diboride addition is a reduction in grain size. The effects of lower volume fractions of titanium diboride have not been examined in detail. However, recent studies at the Howmet Corporation on the effect of the amount of titanium diboride on the microstructure of as cast alloys have shown that the small grain size present in the 7.5 vol% alloys was retained to volume fractions as low as ~0.5 volume percent titanium diboride [3]. The purpose of this study was to determine the effect of lowering the volume fraction of titanium diboride on the workability of a given titanium aluminide alloy, Ti-48AI-2Mn-2Nb.



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