Investigation of Additive Manufactured GRCop-42 Alloy Developed by Directed Energy Deposition Methods

GRCop is an alloy family constructed of copper, chromium, and niobium and was developed by NASA for high heat flux applications. The first of its kind, GRCop-84, was specifically designed for the environments seen in regeneratively-cooled combustion chambers and nozzles [1]. To further increase thermal conductivity while maintaining material strength characteristics, the percentage of alloying elements were cut in half and GRCop-42 was developed. Over recent years, NASA has successfully additively manufactured GRCop-42 with comparable material characteristics to wrought GRCop-42 using a Powder Bed Fusion (PBF) process. Benefits of this process include fabrication of intricate cooling channels as well as a decrease in manufacturing time. However, there are some large disadvantages in using this process. The nature of the powder bed process imposes a strict volume constraint as well as an excessive amount of material inventory required. A Directed Energy Deposition (DED) process addresses these limitations while also speeding up the manufacturing process even more. With little data on how DED performs with GRCop-42, an investigation into the thermomechanical properties was conducted. More specifically, Blown Powder Deposition (BPD, a DED process of jetting atomized material into a high energy laser to deposit material), was used to compare properties to that of the PBF manufactured GRCop-42. The DED manufactured material was found to have less than 0.1% porosity which improved upon the very best porosity results of 0.5% found in the PBF process. This could be explained by imagining all of the voids that must be present in the powder bed whereas the BPD is essentially a mixture of PBF and cold spray techniques. Tensile tests concluded that the DED manufactured GRCop-42 had lower tensile strengths at room temperature while having higher tensile strengths at higher temperature when compared to the PBF results. The generalized trend of such ultimate tensile strengths decreasing with temperature was seen to be comparable to PBF results with less susceptibility to temperature. The results point towards a process capable of producing fully dense parts capable of meeting mechanical strength requirements with some possible refinement of printing parameters. One major drawback of the DED process is the large increase in surface roughness and decrease in accuracy capabilities when compared to the PBF process. It is recommended that more porosity measurements are taken on specimens created using DED which include horizontal layering as opposed to only vertical layering as seen in this study. Also, to reduce on potential surface roughness stress concentrators, it is recommended that more tensile testing is conducted on specimens machined to specification.