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A Cu-Fe2O3 composite coating was deposited on SUS 430 steel via a cost-effective approach of electrophoresis-electroplating for solid oxide fuel cell (SOFC) interconnects application. Oxidation behavior and oxide scale electrical property of the coated steels corresponding to the SOFC cathode environment were investigated. After oxidation for 5 weeks in air at 800 ℃, the oxide scale exhibits a tri-layer structure including an inner layer of Cr2O3, a middle layer of (Cu, Fe, Cr)3O4 and an outer layer of (Cu, Fe)3O4. The results demonstrate that the (Cu, Fe)3O4 spinel converted from Cu-Fe2O3 composite coating not only significantly suppresses the out-diffusion of Cr and reduces the growth rate of Cr2O3, but also lowers the area specific resistance (ASR) of the oxide scales. [ABSTRACT FROM AUTHOR]

The Ni-Mn3O4, Ni-Mn3O4-CeO2, and Ni-Mn3O4-La2O3 composite coatings are deposited on SUS 430 steel via cataphoresis/electrodeposition as the protective coatings of metallic interconnect materials. Oxidation and electrical behaviors of the coated steels are evaluated in the air at 800 °C to investigate the effect of La2O3. A multilayered oxide scale consisting of a surface layer of (Ni,Mn)3O4 spinel, an outer layer of NiO, a middle layer of Ni-Mn-Fe–Cr spinel, and an inner layer of Cr2O3 (1 μm) has thermally grown on the Ni-Mn3O4-La2O3 sample after a 10-week exposure. The NiO exhibits excellent suppression against Cr outward migration. An area-specific resistance of 17.3 mΩ cm2 is achieved. The oxidation kinetics obeys the parabolic law with a rate constant of 1.1 × 10–13 g2 cm−4 s−1. The addition of La2O3 shows highly effective in suppressing the growth of the Cr2O3 layer and enhancing the electrical property of surface scale compared with CeO2. [ABSTRACT FROM AUTHOR]

In an attempt to optimize the properties of FeCoNi coating for planar solid oxide fuel cell (SOFC) interconnect application, the coating composition is modified by increasing the ratio of Fe/Ni. An Fe 1·5 CoNi 0.5 (Fe:Co:Ni = 1.5:1:0.5, atomic ratio) metallic coating is fabricated on SUS 430 stainless steel by magnetron sputtering, followed by oxidation in air at 800°C. The Fe 1·5 CoNi 0.5 coating is thermally converted to (Fe,Co,Ni) 3 O 4 and (Fe,Co,Mn,Ni) 3 O 4 without (Ni,Co)O particles. After oxidation for 1680 h, no further migration of Cr is detected in the thermally converted coating region. A low oxidation rate of 5.9 × 10−14 g2 cm−4 s−1 and area specific resistance of 12.64 mΩ·cm2 is obtained for Fe 1·5 CoNi 0.5 coated steels. • Fe 1·5 CoNi 0.5 coating is deposited on SUS 430 stainless steel by magnetron sputtering. • The tri-layer oxide scale is thermally formed on the Fe 1·5 CoNi 0.5 coated steel. • The oxidation resistance of the steel substrate is improved. • The out-migration of Cr is effectively inhibited. • A low ASR of 12.64 mΩ·cm2 is exhibited. [ABSTRACT FROM AUTHOR]

Initial oxidation behavior of ferritic stainless steel with a sputtered NiFe2 coating for solid oxide fuel cells interconnect application was investigated in air at 800 °C to understand the transformation process from the NiFe2 alloy coating to NiFe2O4 spinel layer. The results indicated that the NiFe2 coating was initially converted to a surface scale with a layered structure consisting of a top Fe2O3 layer followed by NiFe2O4 mid-layer and an NiO inner layer. Cr oxide started to form at scale/steel interface before the coating was completely oxidized. The preferential growth orientation of Fe2O3 on the surface varied with time during the initial oxidation stage. Steel preoxidation prior to coating not only accelerated the oxidation of NiFe2 coating and the growth of NiFe2O4 layer, but also suppressed the orientated growth of Fe2O3. The surface scales on the coated steels were electrically conductive. The oxidation mechanism of the coated steels is discussed. [ABSTRACT FROM AUTHOR]

• Oxidation behaviours of Ni–Fe–Cr alloys with different Cr content were investigated at 960 °C in air. • A tri-layer oxide structure of (Ni,Fe) 3 O 4 /(Ni,Fe,Cr) 3 O 4 /Cr 2 O 3 was developed on Ni–Fe–15Cr alloy. • The continuous Cr 2 O 3 inner layer significantly improved the oxidation resistance of Ni–Fe–Cr alloys. • The layered oxide scale exhibited a good electrical property. • (Ni,Fe) 3 O 4 /(Ni,Fe,Cr) 3 O 4 /Cr 2 O 3 was highly corrosion resistant in molten alumina-cryolite at 960 °C. High temperature oxidation and corrosion behaviours of Ni–Fe–Cr alloys with different Cr contents (Cr = 0, 10, 15 wt.%) were investigated as inert anodes for aluminum electrolysis. Oxidation results at 960 °C in air showed that Ni–Fe–15Cr alloy formed a tri-layer oxide structure with an outer layer of (Ni,Fe) 3 O 4 spinel, a middle layer of (Ni,Fe,Cr) 3 O 4 spinel and an oxidation resistant inner layer of Cr 2 O 3. Simultaneously, the tri-layer oxide scale exhibited good electrical property and corrosion resistance in aluminum electrolysis condition. [ABSTRACT FROM AUTHOR]

Abstract A uniform trimanganese tetraoxide (Mn 3 O 4) coating has been prepared on Ni-coated SUS 430 steel by novel electrophoretic deposition (EPD) approach based on stable Mn 3 O 4 suspension which has been achieved in ethanol medium with iodine (I 2) as dispersant. Different suspension characteristics and deposition kinetics have been systematically studied to optimize the suspension chemistry and deposition process parameters. The suitable EPD conditions including the current density (1 mA cm−2), deposition time (10 s) and I 2 concentration (1.2 g L−1) are applied to deposit uniform nano-Mn 3 O 4 coating. It is also revealed that the deposited mass and the thickness of Mn 3 O 4 coatings can be controlled by adjusting the EPD process parameters. The Mn 2 O 3 /(Mn,Cr) 3 O 4 /Cr 2 O 3 oxide is formed via oxidizing the coated SUS 430 stainless steel and no Cr-containing species migrates outwards. Graphical abstract Image 1 Highlights • The uniform nano-Mn 3 O 4 coatings have been fabricated by EPD approach. • Stable Mn 3 O 4 suspension is prepared using iodine as dispersant. • Optimization of suspension chemistry and process parameters. • The deposited mass and the thickness of Mn 3 O 4 coatings are readily controlled. • Mn 2 O 3 /(Mn,Cr) 3 O 4 layer effectively reduced the Cr 2 O 3 evaporation. [ABSTRACT FROM AUTHOR]

Abstract NiFe 2 alloy coating was applied on SUS 430 steel substrate for solid oxide fuel cell (SOFC) interconnects via magnetron sputtering technology. The coated steel was exposed for 15 weeks in air at 800 °C. SEM/EDS and XRD analysis results indicated that NiFe 2 O 4 spinel layer atop chromia sub-layer was obtained on the coated steel. The top NiFe 2 O 4 spinel layer not only suppressed chromia layer growth, but also exhibited excellent effect on retention of out-migration Cr species. The long term durability of the double-layered scale was demonstrated by the distinct adhesion of the steel/chromia and chromia/spinel interfaces. An area specific resistance (ASR) of 49.25 mΩ cm2 was achieved for NiFe 2 coated steel after 15 weeks exposure. NiFe 2 O 4 spinel thermally developed from sputtered NiFe 2 coating is promising for the FSS interconnects application. Highlights • NiFe 2 alloy coating was deposited on steel using magnetron sputtering technology. • NiFe 2 O 4 spinel was thermally developed from sputtered NiFe 2 coating. • Surface oxide scale adhesion was still excellent after 15 weeks oxidation. • NiFe 2 O 4 spinel reduced Cr out-migration and improved electrical property. [ABSTRACT FROM AUTHOR]

Ni/CeO 2 mulriple coating has been fabricated on SUS 430 steel via electrodepositing approach. 100-h initial and 3-week long-term thermal exposing to air at 800 °C has enunciated that the oxide scale grown on the Ni/CeO 2 coated steel contains an external oxide layer of NiFe 2 O 4 spinel, a middle oxide layer of NiO and an internal oxide layer of Cr 2 O 3 . Simultaneously, dispersive CeO 2 particles embed in the oxide scale. Compared to the Ni coated steel on which the same tri-layer oxide structure without discrete CeO 2 particles grows in the same exposing environment, growth rate of the internal Cr 2 O 3 layer on the Ni/CeO 2 coated steel has been profoundly suppressed, which subsequently lowers the oxide scale area specific resistance (ASR). Enhancement of the oxidation resistance and reduction of the oxide scale ASR are attributed to the presence of CeO 2 . [ABSTRACT FROM AUTHOR]

A Cu coating was deposited on SUS 430 ferritic stainless steel by a low-cost method of electroplating which was employed for the protection of solid oxide fuel cell metallic interconnects. After oxidation, a two-layer oxide scale consisting of an external layer of CuO and an internal layer of Cr 2 O 3 was primarily formed on the coated steel, and a spinel layer consisting of Cu, Cr, Fe and Mn was formed at the CuO/Cr 2 O 3 interface. The CuO outer layer not only suppressed the Cr 2 O 3 scale growth but also served as an effective obstacle against Cr outward diffusion. The coated steels had lower scale area-specific resistances (ASRs) compared to the uncoated steel. The oxidation mechanism and surface scale electrical properties of the coated steel were discussed. [ABSTRACT FROM AUTHOR]

Initial oxidation behavior of SUS 430 steel with a sputtered Mn-Cu coating was investigated in air at 800 °C. It was found that Mn was preferrentially oxidized upon thermal exposure from 2 to 10 min. The surface scale mainly consisted of MnO inner layer and MnO outer layer, although a small amount of Fe was observable in the scale. In addition, CuO developed on the outer surface of the scale after 10 min of oxidation. However, the scale formed on the coated steel upon oxidation for 20-300 min was obviously different from that upon oxidation for 2-10 min. It was composed of a tri-layer containing a top layer of CuO, a middle layer of (Mn,Cu)O with some Fe, and an inner layer of Cr-rich oxide from the outer surface to the interface between scale and steel. With increasing oxidation time, furthermore, the top layer of CuO thickened first and then became thin. The oxidation mechanism was discussed. [ABSTRACT FROM AUTHOR]

MnCu (Mn:Cu = 1:1, atomic ratio) metallic coatings have been deposited by magnetron sputtering on bare and on 100 h pre-oxidized SUS 430 steel for planar solid oxide fuel cells interconnects application. After oxidation at 800 °C in air, the MnCu coating directly deposited on the bare steel has been thermally converted to (Mn,Cu) 3 O 4 spinel with Fe, containing discrete CuO on the outer surface. Nevertheless, the converted (Mn,Cu) 3 O 4 /CuO layer from the MnCu coating deposited on the pre-oxidized steelis almost free of Fe. A double-layer oxide structure with a main (Mn,Cu) 3 O 4 spinel layer atop a Cr-rich oxide layer has been developed on the bare and pre-oxidized steel samples with MnCu coatings after thermal exposure. The outer layer mainly consisted of (Mn,Cu) 3 O 4 spinel has not only significantly suppressed Cr outward migration to the scale surface, but also effectively reduced the area specific resistance (ASR) of the scale. The sputtered MnCu metallic coating is a very promising candidate for steel interconnect coating material. [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]

Abstract: Sputtered coating of a low-Cr Fe–Co–Ni alloy with 0.36wt.% Si has been prepared on the same cast alloy via magnetron sputtering method. The sputtered low-Cr alloy coating with columnar nanocrystalline structure is thermally oxidized in air at 800°C corresponding to the cathode atmosphere of solid oxide fuel cell (SOFC). It is found that the oxidation resistance of the sputtered low-Cr alloy coating is significantly improved in comparison with the cast low-Cr alloy. A double-layer oxide scale is thermally developed on the sputtered low-Cr alloy coating after oxidation for 12 weeks. The outer layer is (Co,Fe)3O4 spinel containing small amount of Ni and Cr. The inner layer is a continuous Cr2O3 layer, followed by oxides of CrNbO4 and Nb2O5. The surface scale formed on the sputtered coating after 12-week thermal exposure demonstrates an area specific resistance (ASR) of 31.97mΩcm2. The sputtered low-Cr alloy nanocrystaline coating exhibits a promising perspective for intermediate temperature SOFC interconnects application. [Copyright &y& Elsevier]

Abstract: Fe–Co–Ni coating is deposited on ferritic stainless steel using a cost-effective technique of electroplating for intermediate-temperature solid oxide fuel cell (SOFC) interconnects application. The steel with Fe–Co–Ni coating has been evaluated in air at 800°C corresponding to the cathode environment of SOFC. The results indicate that the steel with Fe–Co–Ni coating experiences an initially large mass gain, and then the mass gain increases slightly after the first-week rapid oxidation stage. After thermal exposure in air at 800°C, the Fe–Co–Ni coating has been converted into (Fe,Co,Ni)3O4 spinel layer underneath which a Cr2O3 layer is developed from the steel substrate. The outer layer of (Fe,Co,Ni)3O4 spinel has not only suppressed Cr migration outward but also reduced the growth rate of the inner layer of Cr2O3. The steel with Fe–Co–Ni coating exhibits a stable surface oxide scale area specific resistance (ASR) which is much lower than that of the bare steel. (Fe,Co,Ni)3O4 spinel is a promising protective coating for SOFC steel interconnect. [Copyright &y& Elsevier]

Abstract: The nanocrystalline coating of a low-Cr Fe–Co–Ni base alloy with 0.36wt.% Si was deposited on the as-cast low-Cr alloy with identical compositions by means of magnetron sputtering. The effect of sputtered columnar nano-grain structure on the oxidation behavior of the low-Cr alloy was investigated in air at 800°C. It was found that the columnar nano-grain structure significantly lowered the oxidation rate and changed the surface oxide structure of this alloy. The formation of a continuous Cr2O3 inner layer beneath the CoFe2O4 spinel outer layer on the sputtered nanocrystalline coating resulted in a remarkable improvement in oxidation resistance compared to the cast low-Cr alloy. [Copyright &y& Elsevier]

Abstract: Ni–Fe2O3 composite coating was applied onto ferritic stainless steel using the cost-effective method of electroplating for intermediate temperature solid oxide fuel cell (SOFC) interconnects application. By comparison, the coated and bare steels were evaluated at 800 °C in air corresponding to the cathode environment of SOFC. The oxidation investigations indicated that the oxidation rate of the coated steel was close to that of the bare steel after initially rapid mass gain. The mass gain of the coated steel was higher than that of the bare steel owing to the formation of double-layer oxide structure with an outer layer of (Ni,Fe)3O4/NiO atop an inner layer of Cr2O3. The area specific resistance (ASR) of the double-layer oxide scale was lower than that of the Cr2O3 scale thermally grown on the bare steel. [Copyright &y& Elsevier]

Abstract: Ni coating was deposited on ferritic stainless steel by means of magnetron sputtering method for intermediate temperature solid oxide fuel cell (SOFC) interconnects application. The steel with the sputtered Ni coating was evaluated at 800 °C in air corresponding to the cathode environment of SOFC. The oxidation investigations indicated that the oxidation rate of the steel with Ni coating was close to that of the bare steel after 100 h thermal exposure, in spite of its mass gain being higher than that of the bare steel. The oxide scale formed on it consisted of double layers containing an inner layer of Cr2O3 and an outer layer of NiO with (Ni,Fe,Cr)3O4. The area specific resistance (ASR) of the double-layer oxide scale was lower than that of the Cr2O3 scale thermally developed on the bare steel. [Copyright &y& Elsevier]

Abstract: Fe–Ni alloy is electrodeposited on ferritic stainless steel for intermediate-temperature solid oxide fuel cell (SOFC) interconnects application. The oxidation behavior of Fe–Ni alloy coated steel has been investigated at 800°C in air corresponding to the cathode environment of SOFC. It is found that the oxidation rate of the Fe–Ni alloy coated steel becomes similar to that of the uncoated steel after the first week thermal exposure, although the mass gain of the coated steel is higher than that of the uncoated steel. Oxide scale formed on the uncoated steel mainly consists of Cr2O3 with (Mn,Cr)3O4 spinel. However, a double-layer oxide structure with a Cr-free outer layer of Fe2O3/NiFe2O4 and an inner layer of Cr2O3 is developed on the Fe–Ni alloy coated steel. The scale area specific resistance (ASR) for the Fe–Ni alloy coated steel is lower than that of the scale for the uncoated steel. [Copyright &y& Elsevier]

A sputtered nanocrystalline coating of IN738 alloy was obtained by means of magnetron sputtering technique. The oxide distribution was presented of the cast IN738 and its coating after 50 h in air at 1000 °C. The results indicated that the oxide scale formed on the cast alloy consisted roughly of three sections: the top-most section being Cr2O3 and TiO2 mixture, followed by internal aluminum oxide, and scattering beneath which being TiN particles. In the case of nanocrystalline coating, however, only two sections were obvious: the top Cr2O3, TiO2 and NiCr2O4 spinel mixture layer and the inner continuous Al2O3 layer. No internal oxidation and nitridation occurred. [Copyright &y& Elsevier]

A nanocrystalline coating of Ni was deposited on a pure Ni substrate via magnetron sputtering. The oxidation behavior of the Ni substrate and the nanocrystalline coating was studied in air at 700–900 °C. The samples were examined by scanning tunneling microscopy, scanning electron microscopy with energy dispersive X-ray and X-ray diffraction. The mass gain in the coated sample was higher than that without the coating. The study showed that the nanocrystallization in pure Ni promoted oxidation during early stage, after that, the oxidation rates are about the same in samples with or without the nanocrystalline layer. The oxidation mechanism was also discussed. [Copyright &y& Elsevier]

• A CuFe 1.8 alloy is prepared on SUS 430 steel by magnetron sputtering technology. • The conversion of CuFe 2 O 4 layer from CuFe 1.8 alloy is studied at 800 °C in air. • CuFe 2 O 4 spinel grows in different ways with extended time. • The Cr 2 O 3 layer forms at the steel/converted oxide layers interface. This study reports the thermal conversion process of CuFe 2 O 4 coating as a protective layer on chromia-forming steels. A CuFe 1.8 alloy layer is obtained on steel substrate via magnetron sputtering technology, and then sample is exposed to a simulated solid oxide fuel cell (SOFC) cathode atmosphere (in air at 800 °C) for up to 60 min. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that Fe is preferentially oxidized (Fe 2 O 3 externally and Fe 3 O 4 internally). Then, CuO is formed atop Fe 2 O 3 , while the CuFeO 2 grows within the internal oxidation zone. The CuFe 2 O 4 spinel layer further grows in different ways with increasing time. The Cr 2 O 3 layer forms at the steel/converted oxide layers interface after the alloy layer disappears. [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]

In this paper, the corrosion behavior of GH4169 superalloy under alternating oxidation (at 900 °C) and solution immersion (in 3.5% NaCl solution, 30 ± 1 °C) has been studied by SEM, XRD, XPS, and electron probe microanalysis (EPMA). The results show that the alternating environment increases the corrosion rate of GH4169. The reaction of NaCl and Cr2O3 generates various volatile and soluble corrosion products, such as Na2Cr2O7, CrCl3, Cl2, and Na2CrO4, at a high temperature. The destruction of the protective Cr2O3 film leads to the increase of defects in the oxide scale, promoting the formation of oxides, such as NiO and Fe2O3, and changes the composition and structure of the oxide film. After repeated iterations, the mixed oxides will result in the spalling of the oxide film because they can reduce the fracture toughness of the corrosion scale. Therefore, the corrosion is comprehensively intensified. [ABSTRACT FROM AUTHOR]