In cold spray, innovative coating process, powder particles are accelerated by a supersonic gas flow above a certain critical velocity. Particles adhesion onto the substrate is influenced by particle impact velocity, which can change dramatically depending on particle position from the core of the jet. In the present work, an original experimental set-up was designed to discriminate the particles as a function of the levels of velocity to investigate the influence of this parameter on adhesion. Particles at given positions could therefore be observed using scanning electron microscope, which showed different morphologies as a function of impact velocity. High pressure and temperature at the interface during impact were calculated from numerical simulations using ABAQUS Ò . Transmission electron microscope analyses of thin foils were carried out to investigate into resulting local interface phenomena. These were correlated to particle impact velocity and corresponding adhesion strength which was obtained from LAser Shock Adhesion Test.
WOSInternational audienceThis paper proposes a state-of-the-art laser adhesion test. It consists of testing material interfaces with laser-driven shock wave. Since the first demonstration in the 1980s by Vossen, many studies and developments have been done. This paper presents recent experiments and developments on the basic physics involved. Results show the ability of the technique to perform a quantitative adhesion test for a wide range of materials and configurations. Edge effect principle and ultra-short shock wave give perspectives for new applications for multi-layer combination of material. Fundamental principles are evidenced through experiments on bulk ductile materials before demonstrating their application to coated systems
The deposition of cold-sprayed titanium on various substrates is studied in this work. A rather coarse powder of titanium (270 + 45 lm) was sprayed under uniform spraying conditions using a cold spray system onto five different substrates: two aluminum-based alloys (AISI 1050-H16 and AISI 2017-T4), copper, stainless steel AISI 304L, and Ti-6Al-4V. All the spraying experiments were carried out using alternatively nitrogen (N 2 ) or helium (He) as the process gas. Thick coatings were formed on the various substrates, with the exception of the AISI 2017 substrate. When N 2 was used as the process gas, only a few particles remained adhering to the AISI 2017. The thick pre-existing superficial oxide layer on AISI 2017, which was detected by Electron MicroProbe Analysis (EPMA), appeared to prevent adhesion of cold-sprayed titanium particles. The interaction of the sprayed particles with the various substrates was also studied by means of numerical simulations to better understand the adhesion mechanisms. The microstructure and the characteristics of the coatings were investigated. Deposition efficiency and coating density were found both to be strongly improved by spraying helium as the process gas.
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