FY18 Alabama NASA EPSCoR Rapid Response: Characterization of Bi-Metallic Joints Formed by Different Processes

The family of Cr-Cu alloys is used as the liner in high heat flux applications. Alloying considers the addition of Zr, Nb, Co, and Ag to improve the properties. C-18150 is based on Zr additions which promote age hardening to strengthen the alloy. However, subsequent operation at elevated temperatures can result in Ostwald ripening of the precipitates thereby reducing strength. In contrast GRCop-84 is strengthened by Cr2Nb dispersoids which form during solidification. The formation of these dispersoids leaves an almost pure Cu matrix which increases the thermal conductivity. Nickel based superalloy 625 will be evaluated along with the lower strength 300 series stainless steel alloys (SS). Inconel 625 can be operated up to 1500° F (816° C) while SS alloys are generally limited to 900° F (482° C). Although short term operation can extend the use of SS alloys upwards of 1500° F (816° C). Although Ni and Cu form a single-phase alloy, the influence and stability of the alloying elements must be evaluated for operation in a high flux environment. This project has three objectives designed to fully characterize SLM fabricated GRCop 42: 1) Baseline the interfaces of the as-fabricated material combinations by characterizing the microstructure in two orientations using optical microscopy (OM) and scanning electron microscopy (SEM). 2) Evaluate the effectiveness of various heat treatments on NASA supplied samples. Trade off in temperature between the two alloys will be evaluated due to the limitations of the lower melting temperature Cu alloys. After heat treatment, hardness profiles across the interface will be conducted. Miniature specimens will be machined and tested before and after heat treatments. 3) Evaluate stability of the interface following long term exposure to high temperatures simulating the operational environment. As diffusion is expected to occur in Ni-Cu interfaces, elevated temperature tests will be conducted and specimens characterized microscopically and in tension following exposure to evaluate potential Kirkendall effects.

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