Mechanically Blended Al: Simple but Effective Approach to Improving Mechanical Property and Thermal Stability of Selecti
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INTRODUCTION
INCONEL 718 superalloy (IN718) is widely used in the fields of aviation, mechanical engineering, power generation, etc. because of its low cost and excellent mechanical properties at elevated temperatures, particularly its good creep resistance, good fatigue life, and high strength.[1,2] These are achieved by combined effects from (1) solid solution strengthening by the face-centered-cubic (FCC) c phase (a = 3.60 A˚) that is normally enriched with Ni and Co; (2) precipitation strengthening by the (FCC) c¢ phase (a = 3.61 A˚ and
Z.H. ZHANG and Y.H. ZHOU are with the Department of Materials Science and Engineering and Shenzhen Key Laboratory for Additive Manufacturing of High-performance Materials, Southern University of Science and Technology, Shenzhen 518055, P.R. China, and with the Harbin Institute of Technology, Harbin 150001, P.R. China. S.Y. ZHOU and M. YAN are with the Department of Materials Science and Engineering and Shenzhen Key Laboratory for Additive Manufacturing of High-performance Materials, Southern University of Science and Technology. Contact e-mail: [email protected] L. ZHANG is with Shenzhen Polytechnic, Shenzhen 518055, P.R. China. Manuscript submitted January 8, 2019. Z.H. Zhang and Y.H. Zhou contribute to the study equally. Article published online June 5, 2019 3922—VOLUME 50A, AUGUST 2019
enriched with Al, Nb, and/or Ti), and/or the body-centered tetragonal (BCT) c¢¢ phase (a = 3.63 A˚ and c = 7.05 A˚), which is close to Ni3Nb in chemistry; and (3) grain boundary pinning by carbides.[3,4] Topologically closed packed (TCP) hexagonal Laves phase and/or the orthorhombic d phase (a = 5.11 A˚, b = 4.25 A˚ and c = 4.54 A˚), which is enriched with Nb, Cr, Mo, and/or W, might be also present in the microstructure, whose effects, however, are detrimental to the ductility, especially under high temperature conditions.[5] The working temperature limit of the IN718 alloy is ~ 650 C. Above the temperature, the metastable c¢¢ phase will be converted to the d phase (orthorhombic structure), causing a rapid decline in strength and creep property.[6] Thus, it will be important to develop IN718-based material whose limits are beyond 650 C for harsher conditions.[7] Many studies have been conducted for this purpose, and a popular way to solve the problem is to increase the content of strengthening phase c¢ by changing the ratio of (Ti+Al)/Nb, especially Al, as it is known that a fraction of the c¢ phase will increase at higher Al concentrations.[8,9] The increased content of the c¢ phase improves the alloy’s thermal stability by reducing the content of the c¢¢ phase, and it maintains good mechanical properties of the alloy due to low mismatch with the matrix phase.[10,11]
METALLURGICAL AND MATERIALS TRANSACTIONS A
On the other hand, Ni-based superalloys, including IN718, are typical work-hardening materials. This makes their machining difficult. The rapid development of novel advanced manufacturing techniques, particularly selective laser melting (SLM) additive manufacturing (AM), offers a p
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