High-temperature materials for structural applications: New perspectives on high-entropy alloys, bulk metallic glasses,
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Introduction Advances in engines and other applications with hightemperature requirements have been constrained by our limited ability to garner heat losses and improve performance metrics by optimization. In addition, materials researchers are pursuing advanced metallic materials to answer the challenging strength–ductility dilemma. Due to the advantages of their higher toughness and predictable fracture behavior, metals, such as aluminum and titanium alloys, have been used in aerospace applications.1 Recent elevated-temperature alloy developments have raised the bar on high-temperature stability through advances in precipitation hardening and microstructure design. Besides the conventional perspectives for high-temperature metals for structural applications,2–6 new demands for emergent businesses and industries have arisen. For example, while new power technologies have surpassed coal in addressing global warming,7–9 the development of high-temperature alloys for structural applications directly improves thermal efficiency and reduces greenhouse gas emissions, such as those alloys used in ultra-supercritical coal plants that
utilize supercritical fluids and reduce air pollution.10–12 Because increased operating pressures and temperatures are needed, the US Department of Energy Fossil Energy Program requires an increase in the steam temperature for ultra-supercritical steam turbines13 of the coal plants. The increasing need for boilers and other high-temperature metals demands the development of superalloys for elevatedtemperature applications.14 New high-temperature materials are currently approaching 70% or higher of their absolute melting temperatures, which is the upper limit to resist creep and vacancy formation. In structural applications, materials capable of performing under these temperatures, as defined by their percentage of their absolute melting temperatures, are designated “superalloys.” Advances in combustion performance, structural performance, or other performance metrics for a variety of applications are hampered by the lack of availability of alloys that are stable at high temperatures. Although researchers have pushed the envelope on these new alloys, and the world needs to further push for the next generation of alloys.
E-Wen Huang, National Chiao Tung University, Taiwan; [email protected] Peter K. Liaw, The University of Tennessee, USA; [email protected] doi:10.1557/mrs.2019.257
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High-temperature materials for structural applications New perspectives The Gartner Hype Cycle,15 which helps industries and companies predict the maturity and adoption of technologies and applications, reports several new applications that need structural materials for higher operati
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