Dislocation Substructure in the Cold-Rolled Ni-20 Mass Pct Cr Alloy Analyzed by X-ray Diffraction, Positron Annihilation
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TRODUCTION
NI-BASED heat-resistant alloys are strengthened complicatedly by solution elements and precipitations inside the grain and at the grain boundary. These alloys are superior in terms of high-temperature characteristics such as heat resistance, corrosion resistance, oxidation resistance, and creep resistance, and they are utilized in various critical environments including the space industry, pipes in nuclear power plants, aircraft engines, high-temperature boiler piping, and automobile mufflers. In terms of boiler piping, although clean energies such as solar power and wind power are expected to lead the next generation of power generation, fossil fuels will still play an important role as a major energy source. However, the situation will become more serious if there is a large increase in CO2 emissions due to increased consumption of fossil fuels at thermal power plants. Therefore, reducing CO2 emissions is a key factor for realizing a low-carbon society. Thus, high-efficiency thermal power generation is essential to meet the energy demand while protecting the environment and resources. Furthermore, the acceleration of technology development for the coexistence of thermal power generation and CO2 reduction is urgently needed for MITSUHARU YONEMURA, Senior Researcher, is with the Technical Research & Development Bureau, Nippon Steel & Sumitomo Metal Corporation, 1-8 Fuso-cho, Amagasaki, Hyogo 660-0891 Japan. Contact e-mail: [email protected] KOJI INOUE, Associate Professor, is with The Oarai Center, Institute for Materials Research, Tohoku University, 2145-2 Narita, Oarai, Ibaraki 311-1313, Japan. Manuscript submitted March 21, 2016. Article published online August 16, 2016 6384—VOLUME 47A, DECEMBER 2016
sustainable energy in the future. For example, the development of high-temperature-resistant alloys is an important issue for high efficiency under elevated temperatures and pressures. To date, ferritic steels such as STBA24, STBA28, STBA29, and NF12 and austenitic steels such as SUS347, SUS304, and SUS310 have been mainly used for the tubes and pipes exposed to high-temperature steam. However, the creep resistance significantly deteriorates at temperatures over 923 K (650 C). Recently, Ni-based alloys, which have superior creep strength at high temperatures have been developed, and alloys A740, A263, and A617 for boiler tubes have been studied with respect to their practical use[1,2] and the possibility of high efficiency under the elevated temperatures and pressures. The behavior of the dislocation that is induced into the matrix in Ni-based alloys under the elevated temperatures and pressures controls creep deformation; however, the strengthening factors such as precipitation inside the grain and at the grain boundary complicate the deformation mechanism at high temperatures. With regard to the interaction between the precipitate and the dislocation under high-temperature deformation, many studies have been conducted, providing important understanding of the deformation mechanism in Ni-based
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