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La–Cr coating was applied to SUS 430 steel using magnetron sputtering for solid oxide fuel cell (SOFC) interconnects. The coated steel was then thermally exposed to air at 800 °C for 5 weeks. The results showed the formation of a LaCrO 3 layer on top of a Cr 2 O 3 sub-layer on the coated steel. The LaCrO 3 layer not only inhibited the growth of the Cr 2 O 3 layer but also effectively retained out-migrating Cr species. After 5 weeks of exposure, the La–Cr coated steel achieved a surface scale area specific resistance (ASR) of 33.912 mΩ cm2. The thermally developed LaCrO 3 from the sputtered La–Cr coating shows promise for SOFC interconnects application. • A La–Cr coating was applied to SUS 430 stainless steel using DC magnetron sputtering. • LaCr coated steel was subjected to thermal exposure in air at 800 °C to form a LaCrO 3 coating. • LaCr coated SUS 430 was exposed at 800 °C for 5 weeks. • LaCrO 3 layer has significantly suppressed the growth of Cr 2 O 3. [ABSTRACT FROM AUTHOR]

A high-entropy alloy coating of FeCoNiMnCu was prepared on SUS 430 steel via magnetron sputtering for solid oxide fuel cell (SOFC) interconnects application. The coated steels were subject to thermal exposure in air at 800 °C for up to 10 weeks. Phase constituents, microstructure and area specific resistance (ASR) of the coated steel before and after the oxidation testing were investigated. Results indicated the alloy coating was thermally converted into a high-entropy spinel coating of (Fe,Co,Ni,Mn,Cu) 3 O 4 after oxidation and a protective Cr 2 O 3 layer was formed at the steel/coating interface. The (Fe,Co,Ni,Mn,Cu) 3 O 4 spinel coating effectively suppressed growth of Cr 2 O 3 layer and outward diffusion of Cr during the long term exposure. Scale ASR of the coated steel was as low as 6.59 mΩ·cm2 at 800 °C after 10 weeks. It indicates that (Fe,Co,Ni,Mn,Cu) 3 O 4 is a promising coating material for SOFC metallic interconnects. • A high-entropy alloy coating of FeCoNiMnCu is sputtered on SUS430 steel. • The coating is thermally converted into a high-entropy (Fe,Co,Ni,Mn,Cu) 3 O 4 spinel. • The spinel coating effectively suppresses growth of Cr 2 O 3 and out-diffusion of Cr. • Area specific resistance of coated steel is sufficiently low after long term exposure. [ABSTRACT FROM AUTHOR]

A sputtered coating of a low-Cr alloy without Si was deposited on the cast alloy with the same composition. The short term (100 h) oxidation behavior of the sputtered coating and the cast alloy was evaluated in air at 800 °C. The results indicated that the sputtered coating exhibited a higher oxidation resistance than the cast alloy. It was found that the mass gain of the cast alloy increased continuously with oxidation time and was higher than that of the sputtered coating, which demonstrated only a slight increase in mass gain with oxidation time after 5 h thermal exposure. During the initial thermal exposure of 0.5 h, the oxide scale formed on the cast alloy consisted of FeO and (Fe,Co,Cr)O spinel with a small amount of Cr. However, (Fe,Co,Cr)O spinel and FeO were thermally grown on the sputtered coating. After oxidation for 100 h, the oxide scale formed on the cast alloy consisted of CoO and (Fe,Co)O with internal oxide of Cr, while a double-layer oxide consisting of an outer (Fe,Co,Cr)O spinel layer and an inner CrO layer was developed on the sputtered coating. [ABSTRACT FROM AUTHOR]

• Cr x N/Mn 1.7 Cu 1.3 coating is prepared by multi-arc ion plating plus magnetron sputtering. • Mn 1.7 Cu 1.3 layer is thermally converted into highly conductive Mn 1.7 Cu 1.3 O 4 layer. • Cr x N is gradually oxidized to form a Cr 2 O 3 layer at Cr x N/Mn 1.7 Cu 1.3 O 4 interface. • Cr x N layer restrains the interdiffusion between the coating and steel substrate. • Surface scale exhibits excellent electrical property after 15-week exposure. Cr x N/Mn 1.7 Cu 1.3 dual layer coating was prepared on SUS 430 steel via multi-arc ion plating and magnetron sputtering in sequence for use of solid oxide fuel cell (SOFC) interconnects. The coated steel was exposed to air at 800 °C corresponding to SOFC cathode environment to evaluate the oxidation behavior and electrical property of the surface scale. Results indicated that the Mn 1.7 Cu 1.3 outer layer was thermally converted into Mn 1.7 Cu 1.3 O 4 spinel outer layer and the Cr x N inner layer was gradually oxidized to form a protective Cr 2 O 3 layer at the interface of Cr x N and Mn 1.7 Cu 1.3 O 4. After the Cr x N layer was completely oxidized, the surface scale mainly consisted of an outer Mn 1.7 Cu 1.3 O 4 spinel layer and an inner Cr 2 O 3 layer. Area specific resistance of the surface scale formed on Cr x N/Mn 1.7 Cu 1.3 coated steel after 15 weeks oxidation was 17.28 mΩ·cm2. The superior performance of the coated steel benefited from the combination of Cr x N barrier layer and Mn 1.7 Cu 1.3 O 4 spinel. [ABSTRACT FROM AUTHOR]

Ni-Mn 3 O 4 and Ni-Mn 3 O 4 -CeO 2 composite coatings are fabricated on SUS 430 steel via electrophoresis/electrodeposition. The initial oxidation results reveal that the CeO 2 deposited by electrophoresis retards the interdiffusion between coating and steel. Besides thin scale with Cr 2 O 3 inner layer and NiO/(Ni,Mn,Fe) 3 O 4 outer layer, oxide nodules form at the edge of Ni-Mn 3 O 4 coated steel oxidized for 3 weeks. A tri-layer oxide structure with (Ni,Mn,Cr) 3 O 4 outer layer, NiO/(Ni,Mn,Cr) 3 O 4 middle layer and Cr 2 O 3 inner layer is developed on the Ni-Mn 3 O 4 -CeO 2 coated steel oxidized for 10 weeks. CeO 2 effectively improves high temperature oxidation resistance. An area specific resistance (ASR) of 25.1 mΩ cm2 is achieved. • Ni-Mn 3 O 4 -CeO 2 coating is deposited on steel by electrophoresis/electrodeposition. • CeO 2 retards the interdiffusion between Ni-Mn 3 O 4 coating and substrate. • (Ni,Mn,Cr) 3 O 4 /NiO atop Cr 2 O 3 layer is thermally developed on the coated steel. • CeO 2 effectively improves the high temperature oxidation resistance. • The surface scale exhibits a high electrical conductivity by addition of CeO 2. [ABSTRACT FROM AUTHOR]

Ni/NiFe 2 dual layer coating is fabricated to improve the performance of SUS 430 steel as solid oxide fuel cells (SOFCs) interconnects by a combined approach. Ni layer is deposited by electroplating or magnetron sputtering, and subsequently the NiFe 2 layer is sputtered on it. The coated steels are evaluated at 800 °C in air corresponding to SOFC cathode environment. It is found that the coating with electroplated Ni and sputtered NiFe 2 results in breakaway oxidation after 5 weeks. Preoxidation treatment in 900 °C air for electroplated Ni steel prior to depositing NiFe 2 layer improves oxidation resistance. The sputtered Ni and NiFe 2 sample exhibits superior oxidation resistance and inhibition against Cr outward migration while maintaining a low area-specific resistance (ASR) of surface scale. Comparative analyses of the coating preparation and resultant oxidation behavior with possible mechanisms and implications are discussed. • Ni layer is electroplated and sputtered to prepare Ni/NiFe 2 dual layer coating. • Cr out-migration was effectively prevented by the converted oxide coating. • Electroplating Ni reduced oxidation resistance while sputtering Ni enhanced it. • Surface scale of sputtered Ni sample exhibited a better electrical conductivity. [ABSTRACT FROM AUTHOR]

NiFe 2 coating with thickness of 3.5, 6.5 and 9.5 μm was deposited on SUS 430 steel by magnetron sputtering 2 h, 4 h and 6 h, respectively, for application as protective coating of solid oxide fuel cell (SOFC) interconnects. Oxidation and electrical behavior of the coated steels were evaluated in air at 800 °C for durations of up to 15 weeks to investigate the effect of coating thickness. It is found that 4 h and 6 h samples showed better oxidation resistance and Cr-blocking effectiveness compared to 2 h sample. The lowest area specific resistance (ASR) after 15-week oxidation was achieved for 4 h sample. Results suggest that 6.5 μm NiFe 2 coating of 4 h sample exhibited an appropriate thickness for effectively inhibiting Cr out-diffusion and improving the oxidation resistance while maintaining a low scale ASR. • NiFe 2 coatings with different thickness was sputtered on interconnect steel. • Increase of coating thickness enhanced the inhibition against Cr out-migration. • The lowest scale area specific resistance was achieved for 6.5 μm NiFe 2 coated steel. • NiO layer exhibited superior ability to prevent both Cr and Mn out-migration. [ABSTRACT FROM AUTHOR]

• The conversion and evolution of the scale on FeCoNi coated steel is investigated. • Mechanism of the (Ni,Co)O out-migration is discussed. • The scale ASR is predicted for solid oxide fuel cells lifetime by a parabolic law. • The thermally converted coating is chemically compatible with LSCF. The thermal conversion and evolution of surface scale formed on FeCoNi coated SUS430 steel was investigated in static air at 800 °C under isothermal and cyclic conditions. Fe and Co were preferentially oxidized to (Co,Fe) 3 O 4 on the coating surface. Simultaneously, a thin Cr 2 O 3 layer developed at the steel/coating interface. Then (Ni,Co)O developed beneath the (Co,Fe) 3 O 4 layer, and Co 3 O 4 was formed at the outermost layer. (Fe,Co,Ni) 3 O 4 was formed by a solid-state reaction of thermal converted oxides. The discrete (Ni,Co)O gradually migrated outwards through the alternating process between the formation and decomposition of unstable (Fe,Co,Ni) 3 O 4 and finally aggregated close to the outer surface. The (Fe,Co,Ni) 3 O 4 /(Ni,Co)O effectively improved the electrical performance of scale and exhibited adequate compatibility with cathode La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3+ δ. [ABSTRACT FROM AUTHOR]

• Self-sustainable oxychlorination process in Fe-Al coatings is inhibited effectively in Ni-Al coatings. • The formation of gaseous tungsten oxide is greatly inhibited by unaluminised Ni film barrier. • Interdiffusion is largely alleviated due to the smaller indiffusion coefficient in Ni-Al coating. Fe-Al and Ni-Al coatings were prepared by aluminizing ferritic-martensitic steels without and with pre-electroplating a Ni film, respectively. The corrosion behaviour of two aluminide coatings in marine environment, where high temperature oxidation and corrosion occur under the synergistic effect of solid NaCl and water vapour, were investigated. The results indicated that Ni-Al coatings showed superior corrosion resistance to Fe-Al coatings, the improved performance is mainly due to the beneficial influence of the Ni-plating layer on inhibiting self-sustainable oxychlorination, tungsten outward diffusion and interdiffusion behaviour. The detrimental effects of Fe on breakaway oxidation of Fe-Al coatings are discussed. [ABSTRACT FROM AUTHOR]