Deposition and Evaluation of Protective PVD Coatings on Ferritic Stainless Steel SOFC Interconnects

Abstract

Reduced operating temperatures ͑600-800°C͒ of solid oxide fuel cells ͑SOFCs͒ may enable the use of inexpensive ferritic steels as interconnects. Due to the demanding SOFC interconnect operating environment, protective coatings are gaining attention to increase long-term stability. In this study, large area filtered arc deposition and hybrid filtered arc deposition-assisted electron beam physical vapor deposition technologies were used to deposit two-segment coatings with Cr-CoAl -ON based bottom segment and Mn-CoO top segment. The bottom segment serves as a diffusion barrier and bond segment, while the top segment is meant to increase electrical conductivity and inhibit Cr volatility. Coatings were deposited on ferritic steel and subsequently annealed in air for various time intervals. Surface oxidation was investigated using Rutherford backscattering spectrometry, scanning electron microscopy, and energy-dispersive spectrometry analyses. Cr volatilization was evaluated using a transpiration apparatus and inductively coupled plasma-mass spectrometry analysis of the resultant condensate. Electrical conductivity ͑area specific resistance, ASR͒, was studied as a function of time using the four-point technique. Significant improvement in oxidation resistance, Cr volatility, and ASR were observed in the coated versus uncoated samples. Transport mechanisms for various oxidizing species and coating diffusion barrier properties are discussed.

Oxidation Resistant, Cr Retaining, Electrically Conductive Coatings on Metallic Alloys for SOFC Interconnects

“…These results indicate the substrate/coating interface toughening mechanism provided by the dual segment coating architecture. This indicates a significant influence of the lower segment coating on the surface morphology and its evolution [27].…”

“…ASR values for uncoated Crofer 22 APU continue to rise past 40mΩ·cm 2 after ~1,000 hours, while coated samples display relatively stable ASR behavior, with values below ~25mΩ·cm 2 after ~2,000 hours. The upper segment coating alone had the lowest ASR values, while the dual segment coating exhibited the most ASR stability [27]. The continued growth of a chromium-rich scale under the single, upper segment coating is likely responsible for the continued rise in ASR.…”

“…The hybrid LAFAD+EBPVD Mn 1.5 Co 1.5 O 4 spinel system was investigated as a top segment coating because of its SOFC cathode compatibility, its recently reported success in reducing ASR, as well as its anticipated reduction in Cr volatilization [14][15][16]27].…”

“…The single and dual segment coatings were deposited on ~1.6cm 2 x 1mm thick mechanically-lapped and polished (50-80nm nominal roughness by LapRite, Inc) substrate coupons of both commercial 430 stainless steel and Crofer 22 APU by Arcomac Surface Engineering, LLC using a patented Filtered Arc Plasma Source Ion Deposition (FAPSID) technology [7,27,29]. FAPSID employs a rectangular plasma-guide chamber with two rectangular deflecting coils installed on opposite sides, with electron beam evaporators within the chamber, as shown in Figure 2.…”

Avances en el desarrollo de interconectores metálicos de celdas SOFC

“…La espinela (Mn,Co) 3 O 4 se puede aplicar a los materiales interconectores metálicos, por medio de revestimientos (pasta) 57 , impresión de película 55 y PVD 60 . La electrodeposición de aleaciones y/o metales individuales, seguidos por la oxidación controlada y/o reacción de la fase deseada, puede ser un método eficaz para la formación de revestimientos densos.…”