Researchers at theUniversity of Nottingham’s Centre for Additive Manufacturing(CfAM), in collaboration withThe Manufacturing Technology Centre(MTC) andAutodesk Research, have analyzed how interface orientation affects defect formation and microstructure evolution in laser powder bed fusion (LPBF) of IN718 and GRCop-42. Published inAdditive Manufacturing Letters, the study evaluates horizontal, vertical, and angled interfaces to determine how deposition sequence and recoating direction influence alloy mixing and phase formation in aerospace-relevant bimetallic parts.
The work focuses on components such as rocket combustion chambers, where IN718 provides high-temperature strength and GRCop-42, a Cu-Cr-Nballoy developed by NASA, enhances heat dissipation.
Multi-material LPBF using selective powder deposition
To produce the bimetallic samples, the researchers used anAconityMIDI+LPBF system equipped with a 1 kW continuous wave ytterbium fibre laser (80 μm spot diameter) and aSchaeffler Aerosintselective powder deposition (SPD) recoater. The SPD system enables spatially controlled multi-material deposition in a single recoating pass, allowing different powders to be placed in defined regions of each layer.
Samples were fabricated with horizontal interfaces, vertical interfaces, and 45° angled transitions between IN718 and GRCop-42. For each geometry, both deposition sequences were tested. In some builds, IN718 was deposited onto GRCop-42; in others, the order was reversed. The recoating direction was also varied relative to the interface plane to assess how powder spreading affected alloy distribution and interfacial microstructure.
Deposition sequence influences horizontal interface defects
For horizontal interfaces, deposition order proved critical. When IN718 was deposited onto GRCop-42, lack-of-fusion (LoF) defects formed at the interface. Backscatter imaging revealed unmelted IN718 particles. The authors attribute this behavior to the high thermal conductivity of the copper alloy substrate, which dissipates heat rapidly and reduces melt pool temperature. Increasing laser power during the first few IN718 layers mitigated these defects.
Reversing the sequence altered the outcome. Depositing GRCop-42 onto IN718 did not generate LoF defects. Instead, significant alloy mixing occurred at the interface. X-ray diffraction indicated a small additional peak near the interface consistent with a body-centered cubic α-Cr phase in copper-rich regions above the transition line, while electron backscatter diffraction (EBSD) revealed grain refinement and evidence of epitaxial growth.
Recoating direction affects vertical and angled interfaces
For vertical and angled interfaces, the orientation of the interface relative to the recoating direction played a critical role.
Source: 3D Printing Industry
