The weightless environment enables the formation of an alloy’s structure to be driven by diffusion as described by Brownian motion rather than gravity driven sedimentation. A diffusion-driven process encourages molecules to be distributed evenly in the material and results in a more uniform microstructure.

When an alloy, for example, solidifies on Earth, gravity-driven phenomena such as convection, sedimentation, and hydrostatic pressure can significantly impact the material’s internal microstructure. Non-uniform densities in materials can cause the alloying elements in an alloy to separate during phase transitions. Microgravity offers opportunities to promote uniformity within a material’s microstructure because of its independence from convection, sedimentation, and hydrostatic pressure.

Some alloys are challenging to produce on Earth. A class of alloys, known as Superalloys or high-performance alloys, contain heat and wear-resistant metals like tungsten, niobium, and molybdenum. These elements, also called refractory metals, are often employed in high-heat, high-stress environments, such as gas engine turbine blades, nuclear power reactors, and rocket engines.
But the very properties that make these materials attractive (their heat- and wear-resistance) also prevent them from being machined or processed easily on Earth due to their high melting points.

Microgravity enables different methodologies for processing and melting the desired amount of alloy material and allows for better control of microstructure uniformity throughout the alloy. For example, alloy creation can be conducted without a container in microgravity. “Containerless” processing allows researchers to examine the unique properties of refractory metals not easily studied on Earth, and presents a significant opportunity for manufacturing novel, high performance Superalloys.

The weightless environment of the space station also creates opportunities to develop novel alloys that would be almost impossible to fabricate on Earth. On-board research has already stretched the definition of ‘alloy’ with the fabrication of bulk metallic glasses. These non-crystalline metallic alloys have a high degree of hardness but a contrastingly low melting point. As a result, these alloys are extremely durable and highly reflective, but are much easier to process than traditional full-density metals.