Recently, additive manufacturing (AM) became a promising technology to manufacture complex structures with acceptable mechanical properties. The laser powder-bed fusion (L-PBF) process is one of the most common AM processes that has been used for producing a wide variety of metals and composites. Invar 36 is an austenite iron-nickel alloy that has a very low coefficient of thermal expansion; therefore, it is a good candidate for the L-PBF process. This chapter covers the state-of-the-art for producing Invar 36 using the L-PBF process. The chapter aims at describing research insights of using metal AM techniques in producing Invar 36 components. Like most of nickel-based alloys, Invar 36 is weldable but hard-to-machine. However, there are some challenges while processing these alloys by laser. This chapter also covers the challenges of using the L-PBF process for producing nickel-based alloys. In addition, it reports the L-PBF conditions that could be used to produce fully dense Invar 36 components with mechanical properties comparable to the wrought Invar 36.
TopIntroduction
Since its discovery in 1920, Invar 36 is being used in the aerospace and electronic devices industries for its dimensional stability (Yakout, Cadamuro, Elbestawi, & Veldhuis, 2017). Although Invar 36 is a weldable material, it faces the following challenges during laser processing or welding (Corbacho, Suárez, & Molleda, 1998; Yakout, Elbestawi, & Veldhuis, 2018d):
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Internal cracking due to its large heat-affected zone (HAZ).
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Columnar grain formation at high temperatures.
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Presence of inclusions, impurities, and interdendritic precipitates.
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Migration of a grain boundary due to heat transferred from later layers.
The properties of Invar 36 are sensitive to laser processing conditions in laser-based manufacturing processes. Most importantly, the coefficient of thermal expansion (CTE) of additive parts could also be different than that of the wrought Invar 36 (G. Li, Gao, Chen, Zhang, & Zeng, 2014; Tepylo, Huang, & Patnaik, 2019). Accordingly, studying the process-structure-property relationships in laser-based manufacturing processes has been of utmost importance (DebRoy et al., 2018; Fereiduni, Yakout, & Elbestawi, 2019; Gallmeyer et al., 2020; Herzog, Seyda, Wycisk, & Emmelmann, 2016; Smith et al., 2016; Yakout, Elbestawi, Wang, & Muizelaar, 2019a; Yakout, Elbestawi, & Veldhuis, 2018b, 2019b, 2020a; Yan et al., 2018). This chapter focused on the Laser powder-bed fusion (L-PBF) of Invar 36. L-PBF is a common additive manufacturing (AM) process that produces metal parts using a focused laser source (DebRoy et al., 2018; Herzog et al., 2016; Yakout, Elbestawi, & Veldhuis, 2018c). L-PBF of Invar 36 has been presented in the open literature with some challenges (Harrison, Todd, & Mumtaz, 2017; Khanna, Mistry, Rahman Rashid, & Gupta, 2019; Qiu, Adkins, & Attallah, 2016; Wei et al., 2020; Yakout et al., 2018b, 2018d, 2019b; Yakout, Elbestawi, Veldhuis, & Nangle-Smith, 2020b). The L-PBF process is associated with internal cracking, spatter generation, pore formation, vaporization of some of the alloying elements, and residual stress formation (Bai, Yang, Wang, & Zhang, 2017; Collur, Paul, & Debroy, 1987; Fereiduni et al., 2019; He, DebRoy, & Fuerschbach, 2003; Herzog et al., 2016; Khan & Debroy, 1984; Yakout & Elbestawi, 2017, 2019; Yakout, Elbestawi, & Veldhuis, 2018a).
This book chapter focuses on the challenges and manufacturing flaws during the L-PBF of Invar 36. The laser processing conditions that provide stable melting, crack-free microstructures, and minimum residual stresses are discussed. The chapter starts with an introduction to Invar 36 and nickel-based alloys with regards to their properties and applications. Then, it explains the laser processing conditions for Invar 36, including their influences on part quality. It describes the properties of Invar 36 parts, including mechanical, thermal, and surface properties. In addition, applications, promises, and future work roadmaps of Invar 36 produced using additive manufacture are explored at the end of this chapter.