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

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.

Research highlights
► Low net thermal expansion bimetallic structural lattice constructed.
► Temperatures on the order of 1000 °C reached.
► Improved silicide coating for niobium alloy developed.