Cold spray as an innovative process to develop leak tight aluminum coatings for ultrahigh vacuum applications in a large particle high-energy collider

Vacuum chambers used in the experiments of high-energy particle accelerators are conventionally made of bulk beryllium, which shows significant drawbacks due to cost and toxicity. The objective of the present work is to develop cold sprayed Al-coated chamber as an alternative solution. This requires that cold sprayed Al behaves as a perfect vacuum barrier as beryllium. The study focuses on the relation between porosity in the cold sprayed aluminum coatings and leak tightness. Coatings from 0.18% to 9% porosity were achieved, and related to their tightness through helium leak testing. Multiscale porosity was studied, in both 2D and 3D, by SEM, X-ray microtomography and TEM nanotomography. The porosity networks obtained in this way were used for gas flow simulation study at different scale and in different flow conditions. Outputs from modeling are discussed in the light of those from leak tests. In addition, numerical 3D finite element analyses of single and multi-particle impacts were led to go into mechanisms involved in the creation of porosity in cold spray coatings. This study involved different approaches to be compared: an Arbitrary Lagrangian Eulerian method and a coupled Eulerian-Lagrangian one. The porosity rates obtained from simulations will be compared to those from experiments.