Effects of deposition sequence on microstructural evolution in additively manufactured Cu-Cr-Nb alloy / superalloy bimetallic structures

Although Cu-Cr-Nb alloys / superalloys bimetallic components for liquid rocket engine applications have been fabricated using additive manufacturing, a detailed understanding of their process-structure relation is currently lacking. To bridge this gap, GRCop-42 / Alloy 718 bimetallic structures were fabricated with two different deposition sequences, using powder feedstock with a laser-based directed energy deposition process. The deposition sequence resulted in significant variations in precipitate morphology, composition, and crystal structure within the GRCop-42, particularly at locations near the interface. When Alloy 718 was deposited first, dilution and convective mixing resulted in elevated Ni and Fe levels within the GRCop-42 deposit, which contributed to the formation of C14 (Cr, Ni, Fe)₂Nb Laves and α-Cr phases. The anticipated C15 Cr₂Nb precipitates were observed within the GRCop-42 material when the deposition sequence was reversed.