The TaC growth axis was in each case, but the carbide morphology changed progressively across the phase diagram. The decreasing volume fraction can be explained by a lever-arm rule application for the ternary phase diagram, based on the liquidus trough and tie-line compositions determined in this study. The volume fraction of TaC decreased from 6.7 vol pct to 1.7 vol pct as Ta/C increased from 1.3 to 8.8. Volume fraction and microstructural features of the TaC phase were also studied. The matrix compositions and TaC stoichiometries were used to map tie-lines across the ternary diagram. Fiber compositions ranged from TaC 0.99 to TaC 0.97 as the Ta/C ratio of the aligned region increased. Matrix composition was determined by electron microprobe analysis, and lattice parameters of extracted TaC fibers were measured by X-ray diffraction. Ratios of Ta/C atoms varied from 1.3 to 8.8 in the aligned regions. Bulk chemistries were determined for aligned regions to map the liquidus trough compositions. The liquidus trough rises in temperature across the ternary diagram moving away from the Ni−C eutectic (1320☌) and toward the Ni−Ni 3Ta eutectic (1380☌). Alloys were melted with Ta/C atomic ratios of 0.79 to 3.33 in an attempt to define the composition range that would produce two-phase γ+TaC eutectics. The investigation was directed toward developing a detailed picture of γ+TaC composites. The Ni−Ta−C ternary system has been studied at the Ni-rich end of the phase diagram.
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