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http://dx.doi.org/10.7777/jkfs.2016.36.5.167

Effect of Heat-treatment on Microstructure and Tensile Properties in Cast Alloy 718  

Do, Jeong-Hyeon (High Temperature Materials Group, Korea Institute of Materials Science)
Kim, In-Soo (High Temperature Materials Group, Korea Institute of Materials Science)
Choi, Baig-Gyu (High Temperature Materials Group, Korea Institute of Materials Science)
Jung, Joong-Eun (High Temperature Materials Group, Korea Institute of Materials Science)
Jung, In-Yong (High Temperature Materials Group, Korea Institute of Materials Science)
Jo, Chang-Yong (High Temperature Materials Group, Korea Institute of Materials Science)
Publication Information
Journal of Korea Foundry Society / v.36, no.5, 2016 , pp. 167-173 More about this Journal
Abstract
The effect of various types of heat-treatment on the mechanical properties of cast Alloy 718 has been investigated. Cast Alloy 718 bars were subjected to 'standard heat-treatment'_(SHT), 'HIP (Hot Isostatic Pressing) heat-treatment'_(HHT), and 'HIP-simulated heat-treatment'_(HS). In the absence of long time high temperature heat-treatment, a small amount of Laves phase remained in the 'SHT' specimen, and needle shaped ${\delta}$ precipitated in the vicinity of the Laves phase. Due to the formation of the Laves and ${\delta}$ phases in the 'SHT' specimen, it exhibited lower tensile properties than those of the others_specimens. On the other hand, the Laves phase was completely dissolved into the matrix after 'HHT' and 'HS' treatments. It is known that isostatic pressure reduces the self-diffusion coefficient, because of the lower self-diffusivity under HIP conditions in the interdendritic region, Nb segregation and the high amount of ${\gamma}^{{\prime}{\prime}}$ precipitation that occurs. Due to the higher fraction of coarse ${\gamma}^{{\prime}{\prime}}$ phases, the 'HHT' treated Alloy 718 showed excellent tensile strength.
Keywords
Cast Alloy 718; Segregation; ${\gamma}^{{\prime}{\prime}}$ strengthening; HIP; Heat-treatment;
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