Reducing the mass of equipment and machines is vital to making future space missions more efficient and cost-effective.
To do this, innovating new ways of fabricating parts, such as tubular structures with a low density and high mechanical performance, is crucial. One recently closed TDE contract is assessing whether a new way of welding components, called Friction Stir Welding (FSW), could be used to optimise pressure tanks without affecting their structure or useful properties.
The tests, performed on plates made up of a mixed-metal composite called Titanium Silicon Carbide (TiSiC) and a light-weight but strong titanium alloy with 3% aluminum and 2.5% vanadium (originally developed for aerospace tasks), showed that overall FSW is comparable to or better than the standard way of welding in almost every area.
To see if the new welding method held up, the team tried to destroy it with a series of performance tests, which included visual inspection, microstructure, microhardness, tensile, fracture toughness, fatigue crack growth and residual stress.
Overall, the welding survived its attempted destruction with little to no changes – after the tests the welds appeared the same and even X-rays showed no signs of significant cracks or pores. The welds could withstand a tensile strength of 768MPa.
They then made a xenon tank using this welding method. Currently, xenon tanks for space are built using diffusion bonding. This technique operates on the principle of solid-state diffusion – that the atoms of two solid, metallic surfaces intersperse themselves over time. Friction stir welding, however, works on the principle that by creating friction between two materials, it heats and softens the two pieces at the point where they touch, and then a tool is used to mechanically mix the two pieces of metal as if you were mixing two colours of clay.
The tests showed that the FSW was just as strong, if not stronger, in almost all areas (except strain to failure) for holding the tank together.