Bimetallic low thermal-expansion panels of Co-base and silicide-coated Nb-base alloys for high-temperature structural applications

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2011-05, Vol.528 (12), p.3973-3980
• Main Authors: Rhein, R.K., Novak, M.D., Levi, C.G., Pollock, T.M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Bimetals; Coating; Cobalt alloy; Cobalt base alloys; Composite structures; Creep; Exact sciences and technology; Intermetallics; Lattices; Low thermal expansion; Mathematical analysis; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Niobium alloy; Niobium base alloys; Oxidation; Silicides; Superalloys; Thermal expansion
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.02.011

► Low net thermal expansion bimetallic structural lattice constructed. ► Temperatures on the order of 1000 °C reached. ► Improved silicide coating for niobium alloy developed. The fabrication and high temperature performance of low thermal expansion bimetallic lattices composed of Co-base and Nb-base alloys have been investigated. A 2D sheet lattice with a coefficient of thermal expansion (CTE) lower than the constituent materials of construction was designed for thermal cycling to 1000 °C with the use of elastic–plastic finite element analyses. The low CTE lattice consisted of a continuous network of the Nb-base alloy C-103 with inserts of high CTE Co-base alloy Haynes 188. A new coating approach wherein submicron alumina particles were incorporated into (Nb, Cr, Fe) silicide coatings was employed for oxidation protection of the Nb-base alloy. Thermal gravimetric analysis results indicate that the addition of submicron alumina particles reduced the oxidative mass gain by a factor of four during thermal cycling, increasing lifetime. Bimetallic cells with net expansion of 6 × 10 −6/°C and 1 × 10 −6/°C at 1000 °C were demonstrated and their measured thermal expansion characteristics were consistent with analytical models and finite element analysis predictions.