HAZ Liquation Cracking Mechanism of IN-738LC Superalloy Prepared by Laser Solid Forming
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precipitation-strengthened cast nickel-based superalloy IN-738LC is strengthened by precipitating the ordered Ni3(Al,Ti)-c¢ phase in the c matrix. This alloy
JIANJUN XU, XIN LIN, PENGFEI GUO, XIAOLI WEN, QIUGE LI, HAIOU YANG, and WEIDONG HUANG are with the State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, 127 Youyixilu, Xi’an, Shaanxi 710072, P.R. China and also with the Key Laboratory of Metal High Performance Additive Manufacturing and Innovative Design, MIIT China, Northwestern Polytechnical University, 127 Youyixilu, Xi’an, Shaanxi 710072, P.R. China. Contact e-mail: [email protected], [email protected] YUFAN ZHAO is with the Department of Materials Processing, Graduate School of Engineering, Tohoku University, 6-6-11 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan. HONGBIAO DONG is with the Department of Engineering, University of Leicester, Leicester LE1 7RH, UK. Contact e-mail: [email protected] LEI XUE is witn the Xi’an Bright Laser Technologies LTD, Xiyuan, Northwestern Polytechnical University, Western Part of South Second Ring Road, Xi’an 710072, Shaanxi, P.R. China. Manuscript submitted March 12, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
is widely used in the production of hot section components of both land-based and aeronautic gas turbine engine owing to its excellent high-temperature creep properties and remarkable resistance to hot corrosion.[1,2] In addition, laser solid forming (LSF) is a typical laser additive manufacturing technology that provides several advantages over the conventional cast process, such as the absence of dies, no size restrictions, fully dense structures, and high performance.[3,4] However, LSF is a layer-by-layer deposition process, and thus the heat accumulation and the reheating effect of subsequent depositions will cause the deposited layer to undergo a certain high-temperature heat treatment with the maximum treatment temperature close to the melting point. The previously deposited layer, as a heat-affected zone (HAZ), is prone to cracking during the subsequent deposition when the deposited materials present a high cracking susceptibility. Therefore, clarifying the cracking mechanism and avoiding cracking become key factors to ensure the high performance of LSF-fabricated parts. Chen et al.[5] have achieved an LSFed IN-738LC thin-walled component with a reasonably good thermal stability after exposure to high temperature (845 C) for 3 to 6 days. Further, Rickenbacher et al.[6] have produced an IN-738LC part with mechanical properties
superior to cast IN-738LC by selective laser melting (SLM), though cracking, which was found to be unavoidable in this part, limits further improvement of the part performance. The same problem also exists in the LSF-fabricated Rene 88DT alloy,[7] which is also a c¢-precipitation-strengthened nickel-based superalloy, wherein the cracking can be attributed to the high content of Al and Ti in these c¢-precipitation-strengthened superalloys (Al+Ti > 6 wt pct, generally). It should be noted t
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