Microstructure evolution-based design of thermal post-treatments for EBM-built Alloy 718
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Microstructure evolution-based design of thermal posttreatments for EBM-built Alloy 718 Sneha Goel1,* , Enrico Zaninelli2, Johannes Ga˚rdstam3, Uta Klement4, and Shrikant Joshi1 1
Department of Engineering Science, University West, 46186 Trollhättan, Sweden Department of Engineering Enzo Ferrari, University of Modena and Reggio Emilia, 41100 Modena, Italy 3 Quintus Technologies AB, 72166 Västerås, Sweden 4 Department of Industrial and Material Science, Chalmers University of Technology, 41296 Gothenburg, Sweden 2
Received: 7 September 2020
ABSTRACT
Accepted: 17 November 2020
Alloy 718 samples were fabricated by electron beam melting (EBM) additive manufacturing process. The work focused on systematic investigation of response of the material to various thermal post-treatments, involving hot isostatic pressing (HIPing), solution treatment (ST) and two-step aging, to tailor post-treatment procedure for EBM-built Alloy 718. Results showed that HIPing at lowered temperature can be used for attaining desired defect closure while preserving grain size. Subjecting the material to ST, with or without prior HIPing, mainly caused precipitation of d phase at the grain boundaries with prior HIPing decreasing the extent of d phase precipitation. Moreover, results suggest that the utility of ST, with prior HIPing, could be dictated by the need to achieve a certain d phase content, as the typically targeted homogenization after ST had already been achieved through HIPing. Detailed investigation of microstructural evolution during subsequent aging with and without prior HIPing showed that a significantly shortened aging treatment (‘4 ? 1’ h), compared to the ‘standard’ long treatment (‘8 ? 8’ h) traditionally developed for conventionally produced Alloy 718, might be realizable. These results can have significant techno-economic implications in designing tailored post-treatments for EBM-built Alloy 718.
The Author(s) 2020
Handling Editor: Sophie Primig.
Address correspondence to E-mail: [email protected]
https://doi.org/10.1007/s10853-020-05595-2
J Mater Sci
GRAPHICAL ABSTRACT
Introduction Additive manufacturing (AM) through electron beam melting (EBM) powder bed fusion technique has gained growing interest for production of difficult-tomachine materials. One such material is Alloy 718, which is a Ni–Fe-based precipitation strengthened superalloy extensively used in off-shore, aerospace and energy sectors [1, 2]. Although Alloy 718 produced by EBM has been studied for several aspects, such as microstructure, mechanical behavior, residual stress, etc. [3, 4], relatively less attention has been paid on the effect of thermal post-treatments. EBM-built Alloy 718 is typically subjected to thermal post-treatments to enhance the mechanical integrity. Thermal post-treatments typically involving hot isostatic pressing (HIPing) and heat treatments have been developed to reduce defects attributable to gas porosity, shrinkage porosity and lack of fusion, promote desired phase precipitation, etc., to ultimately improve the perfor
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