Laser powder directed energy deposition fabrication and tensile sandwich evaluation of Ti64-C103-GRCop-42 functionally graded materials

Abstract

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.