Alloys with thermal expansion matching to electrolyte materials for solid oxide fuel cells

Abstract

The thermal expansion of the Fe-(30–40) wt.% Ni-(20–30) wt.% Co-(6–10) wt.% Cr alloys matches closely with yttria-stabilized zirconia, often used as electrolyte in solid oxide fuel cells. At the best fit, the difference in the thermal expansion coefficients does not exceed 0.7·10–6 K–1 in the range from room temperature to ~500°C. Significant mismatch begins above 600°C, but the internal stresses this mismatch might cause in the metallic component of the metal/ceramics junctions remain significantly below the yield strength up to the temperatures exceeding the starting temperature of relaxation processes by ~180–240°C. The above alloys are phase stable so that no phase transformations are expected at the cell operating temperatures. Their resistance to corrosion attacks in cathodic and anodic environments is comparable to ferritic steels containing 25–30% chromium. The transfer of chromium from the alloys containing 34% Ni, 30% Co and 6–14% Cr into the La0.6Sr0.4MnO4 cathode material occurs after 400–600 h heating at 900°C. Chromium penetrated to a depth of 20 μm at most.

Formation of the physicomechanical properties in high-strength invar alloys

“…Such mate rials include a new generation of high strength Invar alloys, used for the manufacture of high technology components [3,4]. At the same time, there is a notable lack of high strength multifunctional Invar alloys with good performance and low temperature coefficient of linear expansion.…”

“…Researchers at Nosov Magnitogorsk State Techni cal University, in collaboration with specialists at OAO Motovilikhinskie Zavody (Perm) and Bardin Central Research Institute of Ferrous Metallurgy, have developed a design for a mini mill manufacturing blanks made from high strength multifunctional Invar alloys [4][5][6][7]. The system produces long high strength round and square rod (diameter or side of square 6-30 mm) with excellent performance and physicome chanical properties in combinations that are difficult to obtain, such as low and controllable thermal expan sion, with temperature coefficient of linear expansion (0.2-8) × 10 -6 K -1 ; low and controllable temperature coefficient of the elastic modulus, in the range from ⎯30 × 10 -6 K -1 to +30 × 10 -6 K -1 ; high mechanical strength (σ B ≥ 1200 MPa) and plasticity (up to 30%); high yield point (up to 1400 MPa); high quality in mechanical vibrations (Q factor up to 50000) or high damping (up to 10%); and high corrosion resistance (1-2) and high resistance to corrosion cracking.…”