2026 Rubio Ejchel Ti64 C103 GRCop42 FGM DED

Functionally graded materials (FGMs) provide an avenue to combine two alloys with different primary benefits such as Ti–6Al–4 V (Ti64) and GRCop‑42, which expands the bounds of engineering design possibilities. However, direct grading between Ti64 and GRCop‑42 via laser powder directed energy deposition (LP‑DED) is limited by the formation of brittle Cu–Ti intermetallics. This study utilizes C103 (Nb–Hf–Ti) as a partially successful metallurgical bridge to bypass these deleterious phases. Thermodynamic calculation‑informed design was validated through the fabrication of dense, crack ‑free unidirectional gradients. Mechanical integrity was evaluated using a “tensile sandwich” methodology with digital image correlation. While Ti64–C103 interfaces exhibited superior strength and 45% elongation, the transition from GRCop‑42 to C103 revealed a critical thermal sink effect resulting in brittle cleavage failure due to rapid cooling and unforeseen Cu–Hf compounds. These results establish design rules for Ti‑to‑Cu FGMs and demonstrate the tensile sandwich as a robust protocol for characterizing multi‑material additive manufacturing interfaces.