​Additive manufacturing processes can spur the formation of micro-porosities and specific microstructures, which makes these processes likely to modify the mechanical resistance of the materials used. ArianeGroup turned to Liten, a CEA Tech institute, and LaSie* to investigate the influence of this new manufacturing technique on the resistance of certain parts used in the engines of the company's launchers. 

First, scanning and transmission electron microscopy were used to conduct an in-depth analysis of the microstructure and grain size and distribution of the material being studied. Next, a series of tests were completed to study the mechanisms underpinning the interaction of hydrogen with the metal. A gas permeation test entailed putting hydrogen under pressure upline from a disk made from the material and measuring the flow of hydrogen downline from the disk was completed. Spectroscopy was also used to measure thermodesorption, providing insights into the different ways hydrogen is trapped inside the material. 

An analysis of the mechanical resistance test results and microscope observations were combined with finite-element calculations to determine the potential mechanisms that could negatively affect the resistance of the material. Liten also uses these research techniques in other fields, such as to study the influence of hydrogen content in natural gas on gas utility GRTgaz pipe networks.

*CNRS and La Rochelle University Laboratory for Engineering Science for the Environment