Abstract
Nickel-based superalloys processed by additive manufacturing have demonstrated directional solidification, which has been shown to equal or improve mechanical properties compared to cast and wrought alloys. Inconel 625 cylinders have been manufactured by electron beam melting (EBM) and selective laser melting (SLM) and compared. EBM cylinders were built in the Z-axis direction (parallel to the build direction), and SLM cylinders were built in XY-axis (perpendicular to build direction) and Z-axis directions. The microstructures of as-fabricated as well as fabricated and HIPed cylinders were characterized by light optical metallography (LOM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive (X-ray) spectroscopy (EDS). EBM fabricated components contained columnar plates of ?¢¢ (Ni3Nb) precipitates while SLM components contained columnar arrays of fine ?¢¢ nanoparticles. The EBM fabricated and HIPed samples and SLM fabricated and HIPed samples exhibited equiaxed grains, but both components contained complex arrays of dissimilar precipitates.
Highlights
Over the past decade a variety of additive-layer manufacturing technologies employing electron and laser beam fabrication have demonstrated novel prospects for developing complex and multifunctional components with applications in biomedical, aeronautical, and automotive areas (Cormier, et al, 2004; Murr, et al, 2009; Murr, et al, 2012a)
In both electron beam melting (EBM) and selective laser melting (SLM) processes, columnar architectures are formed parallel to the build direction by γ bct Ni3Nb precipitates, yet the difference in cooling rates of the melt pools in each process significantly alters the size and shape of the precipitates as well as the columnar spacing, column width, and texture
The presence of melt banding does not exist in the EBM microstructure as it does in the SLM microstructure (Figure 2 and Figure 13, respectively)
Summary
Over the past decade a variety of additive-layer manufacturing technologies employing electron and laser beam fabrication have demonstrated novel prospects for developing complex and multifunctional components with applications in biomedical, aeronautical, and automotive areas (Cormier, et al, 2004; Murr, et al, 2009; Murr, et al, 2012a). In contrast to more conventional metal or alloy fabrication involving cast or wrought processing, electron and laser beam processing, especially electron beam melting (EBM) and selective laser melting (SLM) involve new directional solidification concepts as well as novel prospects for microstructure control through the development of scanning strategies or related process variables (Thijs, et al, 2010; Bontha, et al, 2009). These features produce solidification cooling rate and thermal gradient phenomena which contribute to microstructure and microstructural architecture development and resulting mechanical properties. These thermo-kinetic phenomena can influence precipitate or other phase development and transformation in complex ways which differ notably from more conventional thermo-processing
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