**2. Materials and Methods**

All samples have been processed and solidified from the liquid state onboard the International Space Station. In Figure 4 we can see the largest space station in the world—the International Space Station (ISS)—which was created as a result of cooperation between Russia, Canada, the United States, Japan, and 11 other member countries of the European Space Agency, including Germany and is in operation since about 20 years. The microstructure of these samples processed in space under microgravity conditions has been analyzed by SEM (Scanning Electron Microscopy—Zeiss LEO 1550).

**Figure 4.** International Space Station (ISS). Picture taken by a crew member of the space shuttle Atlantis after undocking from the space station (Image source NASA/Crew of STS-132).

The presented structure reconstruction we continued to apply on different microsuperalloy samples, for example, please see Figures 5–8. for the visualization of the space (Figures 5 and 6) and earth (Figures 7 and 8) samples under different magnifications.

An ingot of CMSX-10 was produced from the elemental materials by arc melting. Subsequently, rods were produced by suction casting. Pieces were cut from the rod for EDX investigation and suction casting of spheres of 6.5 mm diameter. The composition and its homogeneity were confirmed by energy-dispersive X-ray spectroscopy (EDX), using an Oxford Instruments Inca X-Sight 7426.

For further information on the EML on ISS, we refer to the literature. The facility, developed and built by airbus defense and space, is centered around a high vacuum experiment chamber that can be operated under high vacuum or in inert gas atmospheres, such as argon or helium. Each sample is stored in an individual sample holder, of which up to 18 are contained in an exchangeable sample chamber with a dedicated sample transport system. For processing, the desired sample can be moved into the experiment chamber. The core of the levitator consists of a coil system (SUPOS coil system) on which two radiofrequency RF generators are connected. One generator is used to produce

a quadrupole field, imposing the positioning forces onto the sample. The second RF generator is used to establish a dipole field for heating the sample. The sample, being loosely confined in a wire cage, was placed within the coils during the experiment, leading to the free and extremely stable levitation of the sample.

CMSX-10 is a third generation single-crystal alloy, developed by Cannon Muskegon for a temperature range of 850–950 ◦C, and is, e.g., used in the Rolls-Royce engine TRENT 800. The composition of the investigated CMSX-10 sample was chosen from Erickson (please see Table 1 for the nominal compositions of the investigated sample).

**Figure 5.** Superalloy with magnification 1.50 KX.

**Figure 6.** Superalloy with magnification of 200 KX.

**Figure 7.** Superalloy with magnification of 104 KX.

**Figure 8.** Superalloy with magnification of 2.00 KX.



#### *2.1. Short Experimental Review on the Differences in Solidification of CMSX-10 in 1g and 0g*

We solidified a CMSX-10 sphere of 6.5 mm diameter in microgravity onboard the international space station. The sample showed high undercooling of about 140 K. Figure 9 shows the corresponding temperature-time diagram recorded for the sample using the EML onboard the ISS. The sample was heated from the solid phase, then molten until fully liquid at the alloys liquidus temperature *T*liq = 1706 K, then the liquid was further overheated until a maximum temperature of about 1900 K. Subsequently, the sample was cooled freely. This way, the sample undercooled about 140 K below its equilibrium melting point. In comparison, a sample was solidified on ground, while placed on a water cooled copper mold. Due to heterogeneous nucleation on the contact area, this represents the case of minimal undercooling. Figure 9 shows the temperature-time diagram recorded during the relevant melt cycle performed on ISS in microgravity of the 6.5 mm sphere of CMSX-10.

**Figure 9.** Temperature-Time Diagram of the melt-cycle performed on the CMSX-10 sphere.

2.1.1. SEM Images of the Surface

We have done SEM images on the surface of two samples:


A schematic overview of the situations is given in Figure 10.

**Figure 10.** Samples and the solidification conditions.

For each series, 5 magnifications (200, 500, 1000, 1500, 2000) have been used to take the images. The images on the 0g sample were taken at a random position, since the sample appears identical in every single spot. The images of the 1g sample were taken on the top face (green arrow in Figure 10).

Images A, C, E, G, and I in Figure 11 are from the 0-g samples. Images B, D, F, H and J on Figure 11 are from the 1-g samples.

Images A, C, E, G, and I in Figure 12 are from the 0-g samples. Images B, D, F, H and J on Figure 12 are from the 1-g samples.

Images A, C, E, G, and I in Figure 13 are from the 0-g samples. Images B, D, F, H and J on Figure 13 are from the 1-g samples.

(**E**) 1000x (**F**) 1000x

**Figure 11.** Series of 5 SEM images of the CMSX-10 surface of the 0-g sample (**A**,**C**,**E**,**G**,**I**) and the 1-g sample (**B**,**D**,**F**,**H**,**J**).

(**C**) 500x (**D**) 500x

(**A**) 200x (**B**) 200x

**Figure 12.** *Cont*.

(**E**) 1000x (**F**) 1000x

(**G**) 1500x (**H**) 1500x

(**I**) 2000x (**J**) 2000x

**Figure 12.** Series of 5 SEM images of the CMSX-10 surface of the 0-g sample (**A**,**C**,**E**,**G**,**I**) and the 1-g sample (**B**,**D**,**F**,**H**,**J**).

(**G**) 1500x (**H**) 1500x

**Figure 13.** *Cont*.

(**I**) 2000x (**J**) 2000x

**Figure 13.** Series of 5 SEM images of the CMSX-10 surface of the 0-g sample (**A**,**C**,**E**,**G**,**I**) and the 1-g sample (**B**,**D**,**F**,**H**,**J**).
