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A laboratory based high resolution x-ray radiograph was developed for the investigation of solidification dynamics in alloys. It is based on a low-power microfocus x-ray tube and is potentially appropriate for x-ray diagnostics in space. The x-ray microscope offers a high spatial resolution down to approximately 5 μm. Dynamic processes can be resolved with a frequency of up to 6 Hz. In reference experiments, the setup was optimized to yield a high contrast for AlCu-alloys. With samples of about 150 μm thickness, high quality image sequences of the solidification process were obtained with high resolution in time and space. [ABSTRACT FROM AUTHOR]

For the first time, isothermal equiaxed solidification of a metallic alloy has been observed in situ in space, providing unique benchmark experimental data. The experiment was completed on board the MASER 13 sounding rocket, launched in December 2015, using a newly developed isothermal solidification furnace. A grain-refined Al–20 wt%Cu sample was fully melted and solidified during 360 s of microgravity and the solidification sequence was recorded using time-resolved X-radiography. Equiaxed nucleation, dendritic growth, solutal impingement, and eutectic transformation were thus observed in a gravity-free environment. Equiaxed nucleation was promoted through application of a controlled cooling rate of −0.05 K/s producing a 1D grain density of ~6.5 mm −1 , uniformly distributed throughout the field of view (FOV). Primary growth slowed to a visually imperceptible level at an estimated undercooling of 7 K, after which the cooling rate was increased to −1.0 K/s for the remainder of solidification and eutectic transformation, ensuring the sample was fully solidified inside the microgravity time window. The eutectic transformation commenced at the centre of the FOV proceeding radially outwards covering the entire FOV in ~3 s Microgravity-based solidification is compared to an identical pre-flight ground-based experiment using the same sample and experiment timeline. The ground experiment was designed to minimise gravity effects, by choice of a horizontal orientation for the sample, so that any differences would be subtle. The first equiaxed nucleation occurred at an apparent undercooling of 0.6 K less than the equivalent event during microgravity. During primary equiaxed solidification, as expected, no buoyant grain motion was observed during microgravity, compared to modest grain rotation and reorientation observed during terrestrial-based solidification. However, when the cooling rate was increased from −0.05 K/s to −1.0 K/s during the latter stages of solidification, in both 1 g and micro-g environments, some grain movement was apparent due to liquid feeding and mechanical impingement of neighbouring grains. [ABSTRACT FROM AUTHOR]

A novel isothermal solidification furnace (XRMON-SOL) has been developed for operation under terrestrial and microgravity conditions, using aluminium-based alloys, in conjunction with real-time in situ X-radiography. The furnace is scheduled to fly on board the MASER 13 Sounding Rocket with a view to investigating isothermal equiaxed solidification under microgravity conditions. The present work provides details of the furnace design as well as detailed analysis of pre-flight terrestrial solidification experiments investigating nucleation and growth characteristics of a thin sample of grain refined Al–20 wt%Cu alloy isothermally solidified at a constant cooling rate of −0.05 K/s. Measurements of nucleation density, nucleation undercooling, grain orientation, grain envelope evolution, primary tip growth velocities, and equiaxed grain interactions are provided. Although the effects of gravity were minimised by choice of sample orientation, we show that such effects can only be eliminated in a microgravity environment. [ABSTRACT FROM AUTHOR]