Atomic-Scale Investigation of the Borides Precipitated in a Transient Liquid Phase-Bonded Ni-Based Superalloy
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AS the critical component materials, Ni-based superalloys are widely used in the hot sections of aero-engines and power generation turbines because of their excellent high-temperature mechanical and corrosion resistant properties. By removing grain boundaries which are weak sections, the operating temperature of superalloys can be further increased. In modern gas turbines, the optimized shape geometry of blades, vanes and other related components become more and more complicated to endure higher temperature since higher operating temperature indicates a better efficiency.[1] The intricate
X.B. HU is with the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 110016, China and also with the Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA. Contact e-mail: [email protected]. N.C. SHENG, J.D. LIU, and X.F. SUN are with the Superalloys Division, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China. Y.M. ZHU and J.F. NIE are with the Department of Materials Science and Engineering, Monash University, Clayton, VIC, 3800, Australia. X.L. MA is with the Chinese Academy of Sciences and also with the School of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, China. Contact e-mail: [email protected] Manuscript submitted October 14, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
shape of the component always exerts difficulties for being cast in single-crystal form without formation of defects, such as stray grains, low-angle grain boundaries and freckles, which will greatly deteriorate the macroscopical mechanical properties.[2–5] In order to overcome the manufacturing problem in fabricating complex components, transient liquid phase (TLP) bonding by joining several separate smaller castings together was developed. This modular approach provides the possibility of selecting different types of materials in different parts of the same component depending on the applied stress and the corrosion resistance needed. In addition, for the integral gas turbines, damage of some component is unavoidable during service in extreme environment. Thus, as an economical way, repairing of damaged component is necessary in order to extend the total life, where TLP also finds wide applications. Based on above facts, interest in TLP bonding technique has increased over the last few years.[6–14] In contrast to the widely used welding technique, TLP bonding is more suitable in jointing the highly alloyed engineering materials, such as Ni-based superalloys because of its combined beneficial effect of liquid phase jointing and diffusion bonding.[7,8] In TLP bonding of Ni-based superalloys, boron (B) was considered as an ideal MPD element due to the formation of eutectic with Ni and its rapid diffusion in superalloys substrate.[15] However, solubility of B in superalloys matrix is as low
as ~ 100 ppm.[16] Therefore, precipitation of borides in the vicinity of the joint is una
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