University of Birmingham
Advanced concentrated solar plants (CSP) aim to integrate CSP particle system into highly efficient supercritical carbon dioxides (s-CO2) Brayton power cycles to achieve higher turbine inlet temperature and to push the boundary of thermal efficiency. However, this design creates many challenges for the heat exchange tubes, including resistance to erosion, oxidation and s-CO2 corrosion at >700°C. Chromium (Cr) based materials are sought for CSP applications due to its high melting point (~400°C > nickel/iron), low price (<Ni/other refractory metals) and good oxidation resistance. But the poor mechanical properties and brittleness at room temperature limit their applications. Mirroring to the gamma/gamma’ of nickel superalloys, recently developed Cr superalloys following a "bcc-superalloy” design strategy, comprising a bcc ferritic matrix with B2 NiAl / L21 Heusler Ni2AlTi intermetallic precipitates, have been shown to have significant improvement in strength and creep resistance. This work presents intermetallic (B2, Nickel Aluminide) precipitate strengthened (A2) chromium matrix, creating beta/beta’ superalloys. Alloys were produced using arc melting, heat treated to produce beta/beta' microstructure, and electrical discharge machining sectioned for mechanical tests. High Temperature compression and small punch were performed to investigate their mechanical properties including ductile-brittle transition temperature (DBTT), yield strength and creep resistance. The deployment of chromium superalloys into CSP, the design of the beta/beta’ Cr superalloy, and the investigation of their mechanical properties will be presented.
Abstract
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