This IMPRESS experiment will give the science team a chance to answer two important questions:

How does gravity affect the alloy’s behaviour, as it transforms from liquid to solid?
And how does this shape the structure that forms during this solidification process?

By varying different process parameters such as temperature gradients, it becomes possible to study other phenomena such as structural transition, segregation of alloying elements and effects due to adding small nucleating particles, known as grain refiners.

The sounding rocket furnace of MAXUS-8 enables the simultaneous processing of four titanium-aluminide samples at different boundary temperatures up to a maximum of 1,700°C.
Comparison between sounding rocket and ground experiment samples will help pinpoint the effects of gravity on casting alloys. These results are of paramount importance for industrial applications and will be exploited to enhance the predictive capability of computer models applied to commercial casting processes. All these studies will ultimately help the production, of a new generation of lightweight and fuel-saving turbine blades for aeroplane jet engines with half the density of conventional turbine blades.

The module flown on MAXUS 8 contained four integrated furnaces, working independently from each other. Each furnace was equipped with three in-line resistance heaters.
Two different TiAlNb sample materials have been processed. One refined with Boron the other one without refinement. Both samples were redundant to test the reproducibility. The samples were enclosed in an yttrium oxide crucible and of 8 mm diameter and 165 mm length. Temperature measurement was done by four Thermocouples and the thermal data was retrieved for experiment analysis.
The furnaces were heated up, including pre-heating of the samples to below melting temperature before lift-off, and temperature gradients have been established along the axis of the sample by applying different temperate values to each heater. Complete directional solidification was reached by subsequent cooling (power-down technique) within the microgravity time of the MAXUS flight.

The module contained in four identical high temperature furnaces 2 pairs of identical samples. Three out of four furnaces showed nominal performance while one furnace had a short-cut on one of the heater coils so that the experiment could not be processed as planned. This failure had a slight thermal impact on another furnace as well.
The in-depth analysis of the flight samples, i.e. thermal data and microstructure analysis, consisted therefore of one refined and one non-refined sample. The microstructure analysis of the samples have been performed by state-of-the-art metallographic techniques and revealed the following:

• Applying the same thermal gradients as well as the same cooling rates, the results clearly show differences in the microstructure of the refined and non-refined sample.
• The unrefined sample displays a columnar dendritic growth pattern. The columnar dendrites are growing in axial direction, a behavior that was expected. However longer into the experiment duration the radial columnar growth becomes dominant generating a V-shape microstructure at this transition point. The refined sample shows a fully equiaxed grain structure.

The results will now be used by project partners to validate their numerical models.
The evaluation of and comparison with ground reference experiments performed in the spare flight furnaces is ongoing.

article on the ESA website:
Hypergravity helping aircraft fly further - 5 November 2012