Microstructural Characterization and Analysis of Laser-Powder Bed Fusion GRCop-84 by Metallurgical and Neutron Scattering Methods

GRCop-84 or Cu-8Cr-4Nb (atomic %) is a structural high-heat-flux Cu alloy that is dispersion strengthened by C15 Laves Cr₂Nb [Niobium Chromide] that has seen significant development with laser additive manufacturing (AM), specifically laser-powder bed fusion (L-PBF) in recent years. A review of the development, properties, and performance of GRCop alloys has been conducted and provides pertinent background. The body of research provides fundamental understanding regarding microstructure evolution and phase interaction of GRCop-84 through characterization by neutron and X-ray scattering and metallographic techniques. This research is intended to bridge fundamental research of L-PBF, Cu alloys, structural thermal conductors, and ex-situ and in-situ neutron diffraction techniques. Little is understood regarding the additive microstructure evolution and phase interaction in the Cu-Cr-Nb system. Understanding of melting and crystallization behavior are critical to laser-based processing and can be used to improve the final performance and properties. The microstructure and phases of GRCop-84 have been characterized with scanning electron microscopy (SEM), back-scattered diffraction (EBSD), and X-ray diffraction (XRD). Residual stress mapping with constant wavelength neutrons revealed unexpectedly high residual stress in the Cu matrix that should exceed the yield strength. The high loading of Cr₂Nb [Niobium Chromide] is theorized to provide significant balancing of stress to the Cu phase which allows for relatively easy processing and evidence to this persists in time of flight (TOF) diffraction results where both phases are visible.