Cr-based Alloys

Cr base alloys BCC 11-12.5 Good High Difficult Very expensive... 

Fe-Ni-Cr base alloys FCC 15-20 Good High Readily Fairly expensive... 

Ni(-Fe)-Cr base alloys FCC 14-19 Good High Readily Expensive... 

Other categories of chromia forming alloys—including Ni(-Fe)-Cr base and Fe(-Ni)-Cr base alloys (e.g., austenitic stainless steels)—have a face-centered cubic (FCC) substrate structure. In comparison to the FSS, the FCC base alloys, in particular the Ni(-Fe)-Cr base alloys, are generally much stronger and potentially more oxidation resistant in the SOFC interconnect operating environment [6, 123-129], However, the FCC Ni(-Fe)-Cr base alloys with sufficient Cr for an appropriate... 

Nevertheless, Ni(-Fe)-Cr base alloys may find application as interconnect materials through the use of innovative SOFC stack and seal designs and novel interconnect structures. For example, a cladding approach has been applied to fabricate a stable composite interconnect structure consisting of FCC Ni-Cr base alloy claddings on a BCC FSS substrate [134,135], The clad structure appeared to be stable over 1000 hours at 800°C in air and exhibited a linear CTE close to that of the FSS, but needs further long-term stability evaluation before its commercial use. 

Early works were typically carried out using single atmosphere exposure conditions, either air (or moist air) representing the cathode side environment [124-129, 139, 142,144-162] or a reducing atmosphere simulating the anode side environment [124, 125, 127-129, 144, 145], Lately, studies have been also performed to determine the oxidation/corrosion behavior of metal and alloys under dual-atmosphere exposure conditions that closely simulate the interconnect exposure conditions during SOFC operation [154-159], The alloys studied include both Fe-Cr base FSSs and Ni or Ni-Cr base heat-resistant alloys, as well as Cr or Cr base alloys. 

Despite the experience of the EADS with Pt-based alloys and their good acceptance, the increasingly competitive satellite market demands structural materials with lower prices that nevertheless must remain chemically stable (no coating). This motivated research in the field of Cr based alloys. 

Comparison of chromium exposed to atmospheric air at 1600°C with chromium exposed to combustion chamber solicitations (figure 8) permitted to conclude that mechanisms responsible for the material failure were similar for both cases so testing in high temperature air is a representative method to obtain qualitative results on chemical resistance of Cr-based alloys to combustion chamber gasses. 

Fig. 2 shows the oxidation behaviour of alloys JS-1 and JS-3 (batches UNA and JEX) oxidized in both air and simulated anode gas. A general tendency is that the oxide scales formed in anode gas are slightly thinner than those formed in air. As has previously been reported for Cr-based alloys... 

HfB2> NbB2, and TaB2 and Ni-Co-Cr based alloys. The refractory and extraordinarily hard MB2 phases are hence in equilibrium with a comparatively soft and brittle ternary compounds. 

Keywords Intermetallics, Ni-based alloys, Cr-based alloys, Metallothermic process... 

There are several candidate metaUic materials proposed as follows [4, 5] Ni-Cr alloy, Fe-Cr alloy, and Cr-based alloys. Traditionally, Ni-Cr alloys are high temperature resistant materials, such as Incoimel, Hastelloy, and Haynes. Fe-Cr (ferritic) alloys are often used as high temperature metallic components, such as stainless steel (SUS), E-Brite, ZMG-series, and Crofer-series. Cr-based alloys are specially developed for SOFC intercoimects, which contains oxide materials, such as Cr-Fe-Y203. 

Metal interconnects typically made of ferritic alloys have slightly higher thermal expansion coefficients than YSZ. A new alloy was produced so as to fit the thermal expansion of YSZ this is a Cr-based alloy, Cr5Fel Y2O3 [39]. Since this alloy is oxide dispersed and therefore quite hard, it is not easy to fabricate it into a desired shape. For this purpose, powder metallurgy process has been developed [40]. 

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