Bimetallic low thermal-expansion panels of Co-base and silicide-coated Nb-base alloys for high-temperature structural applications |
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Authors: | R.K. Rhein M.D. NovakC.G. Levi T.M. Pollock |
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Affiliation: | a Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, USA b Materials Department, University of California, Santa Barbara, CA 93106-5050, USA |
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Abstract: | 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. |
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Keywords: | Oxidation Low thermal expansion Composite structures Cobalt alloy Niobium alloy |
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