Session: 18-05: Failure Prediction & Life Assessment II

Paper Number: 153876

High-Temperature Mechanical Performance and Microstructural Development in Nickel-Based Alloy 617 Diffusion Bonds for High-Efficiency Heat Exchangers 

Microchannel heat exchanger technology is being developed for next-generation concentrating solar power (CSP) systems to enable primary supercritical CO2 (sCO2) power cycle heat addition. The economic viability of these plants hinges on a high-efficiency heat exchanger that can last 30 years, resisting creep, fatigue, corrosion, and erosion, while also handling thermal cycling. However, the longevity and operational limits of microchannel heat exchangers, especially those made from high-nickel alloys, remain unclear in part because the long-term performance of the diffusion bonds is not well characterized. These compact heat exchangers are constructed by diffusion bonding of thin metallic etched sheets, where grains of the base material grow across sheet interfaces under high temperatures and pressures. This manuscript explores the use of Inconel alloy 617 (IN617) in manufacturing diffusion-bonded heat exchangers, focusing on the mechanical properties of an IN617 diffusion-bonded test block subjected to tensile, creep, and fatigue testing. Prior work on Ni-Cr, and Fe-Ni-Cr alloys utilized Ni-interlayers which showed debits in creep strength, fatigue, and ductility compared to wrought materials.  In this work, room and elevated temperature tensile testing of a new direct bonded process without interlayers demonstrated excellent repeatability, with good ductility and strength comparable to wrought IN617 material. Based on these findings, a more extensive test program was initiated.  Creep tests show good ductility across various temperatures, with rupture life and creep strain responses similar to wrought IN617. Fatigue performance exceeded the minimum design curves within ASME Section III, though a creep-fatigue debit was observed with a 30-minute hold-time. Ongoing pre- and post-test material characterization aims to identify key microstructural features of IN617 diffusion bonds, quantify grain growth, and understand potential high-temperature damage modes that could affect component performance. This effort provides critical materials data to enable improved life prediction of CSP heat exchangers and ensure quality control in the manufacture of high-temperature diffusion bonds for advanced power cycle applications such as sCO2 turbomachinery.

 

This research was supported by the U.S DOE Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office (SETO) under contract DE-LC0000003.

Presenting Author: Nikki Harless Electric Power Research Institute

Presenting Author Biography: Ms. Nikki Harless is a Materials Scientist IV at the Electric Power Research Institute (EPRI). She has experience in materials characterization, microscopy, failure analysis, and advanced manufacturing with a demonstrated history of working in the nuclear power, aviation, and aerospace industries. She has prior and current experience supporting technical work scopes on collaborative DOE-sponsored research including CSP and advanced manufacturing microstructural characterization. More recently she was the EPRI lead researcher and author of a paper discussing the impact of three additive manufacturing techniques (Laser-Based Power Bed Fusion, Binder Jet, and Wire-DED) on microstructure and creep damage development in Alloy 718. She was also the EPRI lead author for a supply chain workshop summary report which included identification of challenges and opportunities for codes & standards with DED-AM.

Authors:

Nikki Harless Electric Power Research Institute
John Shingledecker Electric Power Research Institute
Bonnie Antoun Sandia National Laboratories
Dereje Amogne Vacuum Process Engineering, Inc. (VPE)
Kevin Albrecht Vacuum Process Engineering, Inc. (VPE)
Matthew Sandlin Sandia National Laboratory - Concentrating Solar Technologies