Thermal and Irradiation Creep Behavior of a Titanium Aluminide in Advanced Nuclear Plant Environments
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INTRODUCTION
INTERMETALLIC titanium aluminides are a relatively young class of structural high-temperature materials compared with steels or nickel-base alloys. They combine good high-temperature strength, creep properties, and low density, which makes them candidates for automotive and energy applications. Typical examples are engine parts, turbine blades,[1,2] and turbochargers.[2,3] Besides their low room-temperature ductility, they are mainly limited by their low oxidation resistance above about 800 C. This limits possible applications to temperatures below their mechanical capabilities. Recent international projects for advanced nuclear fission plants, such as the international generation IV initiative (GIF), search for materials for operating conditions that are different from the ones known for conventional light water reactors. New nuclear power plants will operate at higher temperatures and higher doses and in different environments (helium, liquid metal, molten salt). They are also intended to operate as combined cycle plants for PER MAGNUSSON, Scientist, JIACHAO CHEN, Senior Scientist, and WOLFGANG HOFFELNER, Leader, are with the High Temperature Materials Project, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland. Contact e-mail: wolfgang.hoff[email protected] This article is based on a presentation given in the symposium ‘‘Materials for the Nuclear Renaissance,’’ which occurred during the TMS Annual Meeting, February 15–19, 2009, in San Francisco, CA, under the auspices of Corrosion and Environmental Effects and the Nuclear Materials Committees of ASM-TMS. Article published online September 11, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
electricity production and heat. Suggested reactor technologies are outlined in the roadmap of the GIF.[4] A very-high-temperature reactor (VHTR) and gas-cooled fast reactor (GFR) operate at high temperatures and use helium as a coolant. An environment such as helium could provide a basis for the use of intermetallics at its strength limits rather than at its oxidation resistance. The fact that the material can be cast would, in principle, allow simple and relatively cheap production of components (control rod elements, heat exchanger parts, etc.). While the creep properties at intermediate temperatures have been studied in numerous publications,[1,5–10] the data of creep properties at temperatures above 800 C are still scarce in the literature. Therefore, information on high-temperature creep is very important for the evaluation of c-TiAl as structural material for helium-cooled reactors. The evaluation of c-TiAl for nuclear applications also requires knowledge of irradiation properties. Irradiation creep was investigated using helium implantation. This method limits the sample thickness to 200 lm to obtain the required through irradiation. Based on these data and the existing literature data, an assessment of the mechanical capabilities of this cast titanium aluminide for structural applications in advanced nuclear plants is performed. Comparisons will be made
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