M. Yandouzi

Aircraft Skin Restoration and Evaluation

The recent development of the cold spray technology has made possible the deposition of low porosity and oxide-free coatings with good adhesion and with almost no change in the microstructure of the coated parts. This focuses on the use of low-pressure cold spray process to repair damaged Al-based aircraft skin, aiming at obtaining dense coatings with strong adhesion to the Al2024-T3 alloy. In order to prove the feasibility of using of the cold spray process as a repair process for aircraft skin, series of characterisation/tests including microstructures, microhardness, adhesion strength, three-point bending, surface finish, fatigue test, and corrosion resistance were performed. The obtained results revealed that the low-pressure cold spray process is a suitable for the repair of aircraft skin.

Oxidation Behaviour of Conventional and Nanocrystalline CoNiCrAlY Bond Coats Manufactured by Cold Spray

The purpose of the present study is to investigate and compare the oxidation behaviour of conventional and nanocrystalline CoNiCrAlY bond coats. The nanocrystalline feedstock powder is produced from the conventional feedstock powder using the cryogenic milling process. Conventional and nanocrystalline bond coats are produced using the Cold Spray (CS) process in order to avoid the onset of thermally induced grain growth and minimize the inclusion of oxides in the bond coat microstructure. The oxidation behaviour of free-standing CoNiCrAlY coating samples is determined by means of isothermal oxidation experiments consisting of heat treatments in air at 1000°C for various periods of time. Characterization of the feedstock powders and resulting CS coatings, as well as investigation of the oxide scale growth dynamics, is achieved by means of SEM, XRD and TEM analyses. Mass gain measurements were also carried out throughout the oxidation tests to evaluate oxide growth rates.Copyright

Enhanced reactivity of mechanically-activated nano-scale gasless reactive materials consolidated via the cold-spray technique

The present study presents a novel method to prepare nano-scale energetic materials with high reactivity, vanishing porosity, structural integrity and arbitrary shape. The experiments have focused on the Ni-Al system. To increase the reactivity, an initial mechanical activation was achieved by the ball milling technique. The consolidation of the materials used the supersonic cold gas spray technique, where the particles are accelerated to high speeds and consolidated via plastic deformation upon impact, forming activated nanocomposites in arbitrary shapes with close to zero porosity. This technique permits to retain the microstructures in the powders and prevents any reactions during the consolidation phase. The material reactivity is addressed through the flame propagation velocity, which showed an increase in the flame speed of the cold sprayed samples by up to one order of magnitude compared to their cold pressed counterparts.