In this study, fine aluminum powder was cold sprayed onto aluminum substrates, some of which were polished, some grit blasted, and some pretreated using a nano-pulsed Nd:YAG laser. In the latter case, the laser is coupled with the cold spray gun and the irradiation treatment occurs just prior to deposition. To better understand the interaction mechanisms involved with laser pretreating, coating-substrate interfaces were examined on thin-foil specimens and adhesion strength was determined by laser shock testing. The results show that substrate pretreatment with a nano-pulsed laser significantly improves the coating-substrate interface as well as coating adhesion.

The aim of this study was to investigate the microstructure (including surface roughness, microstructure and microhardness) of cold sprayed copper coatings on 2017 Al alloy, before and after annealing at 350°C for 1h. It seemed that keeping constant the powder flow rate and increasing the gas pressure from 2.0 to 2.5 MPa, the surface roughness of the coating tended to decrease, while the thickness of the coating tended to increase. Also, it seemed that keeping constant the pressure and increasing the powder flow rate from 22 to 130 g/min, the surface roughness and the thickness of the coating tended to increase. The microstructural study of the coatings after etching revealed particle interfaces and in some cases grain boundaries. Twins were observed in some of the coatings. Negligible porosity, absence of cracks and good adhesion of the coatings to the substrate were observed. The microhardness of the coatings varied between 95 HV 0.3 and 150 HV 0.3 for the different employed cold sprayed conditions. After coatings’ annealing the microhardness of all the coatings (cold sprayed and HVOF sprayed) decreased. The aforementioned results were compared with those of HVOF coating.

During the deposition of metallic cold sprayed coatings, it could be observed that only a thin layer is formed on the substrate and further building-up of a thick coating is not enabled. As for other thermal spray techniques, the formation of cold sprayed coatings can be divided to two stages: the creation of the first layer onto the substrate and the building-up of the coating itself onto as-sprayed layers. This two-stage build-up process was evidenced according the study of two Ti-6Al-4V powders exhibiting different characteristics (particle size, morphology, oxygen content, hardness, etc) which were sprayed by cold gas dynamic spraying onto substrates of different nature with various hardnesses (Ti-6Al-4V, AISI 304L, Al-alloy 2017). The phenomenology of the two-stage process is investigated in the present study. Cold spray conditions with pure nitrogen or pure helium as processes gas were applied to achieve a significant difference for particle velocities. The first stage of the process was completed by both powders with the formation of a first coating layer onto the various substrates. However, very different features for particle-substrate interactions (penetration depth and comparative deformation) were observed. For the particle-particle interaction (the second stage of the process), despite similar spraying conditions for both powders, the results were completely different since the formation of thick coating was achieved only with one of the powders. It was found that the intrinsic ductility of the material powder is the main parameter to promote the successful completion of both stages in order to achieve thick coatings.

The demand of industry for metallic thermal sprayed coatings with controlled porosity until now is fulfilled by the spraying of metallic powders mixed with additives (organic element in many cases) which play the role of pores. The new technology of cold spray can lead to the formation of innovate coatings of controlled porosity by using pure metallic (or alloy) powder without any further addition. A fine Al-12Si powder (<45 µm) was sprayed with a cold spray system (CGT Kinetic 3000-M) on stainless steel substrate under different spraying conditions. In the present study, the new polymeric nozzle PBI-33 of CGT was used for the formation of al-based coatings. The microstructure, the porosity, the Vickers microhardness and the superficial Rockwell hardness (R15Y) of the produced coatings are examined.