Abstract
The selective laser melting (SLM) process was used to fabricate an Alloy718 specimen. The microstructure and creep properties were characterized in both the as-built and post-processed SLM materials. Post-processing involved several heat treatments and a combination of hot isostatic pressing (HIP) and solution treatment and aging (STA) to homogenize the microstructure. The experimental results showed that the originally recommended heat treatment process, STA-980 °C, for cast and wrought materials was not effective for SLM-processed specimens. Obvious grain growth structures were obtained in the STA-1180 °C/1 h and STA-1180 °C/4 h specimens. However, the grain size was uneven since heavy distortion or high-density dislocation formed during the SLM process, which would be harmful for the mechanical properties of SLM-fabricated materials. The HIP+ direct aging process was the most effective method among the post-processes to improve the creep behavior at 650 °C. The creep rupture life of the HIP+ direct aging condition approached 800 h since the HIP process had the benefit of being free of pores, thus preventing microcrack nucleation and the formation of a serrated grain boundary.
Highlights
The IN718 superalloy is widely used in gas turbine and related aerospace applications due to its excellent mechanical properties and structural stability at elevated temperatures [1,2,3]
As shown in [9], Amato et al indicated that post-treatments may promote the formation of secondary precipitates, namely, Laves and carbides, which will affect the mechanical properties of the Inconel625 superalloy built up by selective laser melting (SLM)
The objective of this study is to analyze the effects of post-processes on the microstructure and creep properties of Alloy718 built up by the SLM process
Summary
The IN718 superalloy is widely used in gas turbine and related aerospace applications due to its excellent mechanical properties and structural stability at elevated temperatures [1,2,3]. IN718 components produced by conventional processing techniques are limited in terms of their potential complexity and, in their operating range and efficiency [4]. Additive manufacturing processes such as selective laser melting (SLM) offer several advantages in comparison to conventional processing techniques, such as a large degree of design flexibility and reductions in the number of production steps, lead time, and investment cost [5,6,7,8]. As shown in [9], Amato et al indicated that post-treatments may promote the formation of secondary precipitates, namely, Laves and carbides, which will affect the mechanical properties of the Inconel625 superalloy built up by SLM. In our previous experience with the solution treatment and aging (STA) process (980 ◦ C/1 h), Materials 2018, 11, 996; doi:10.3390/ma11060996 www.mdpi.com/journal/materials
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