Low-pressure cold spray has been used as an innovative method to deposit metal matrix composite (MMC) coatings: boron carbide-nickel (B4C-Ni) and tungsten carbide-cobalt-nickel (WC-Co-Ni) composites. The coatings were studied using scanning electron microscopy, X-ray diffraction with Rietveld refinement, and acoustic emission-coupled four-point flexural test. Indentation fracture toughness tests were performed on the WC-Co-Ni coatings, only. The results showed that the composites had reinforcing particle volume fractions of 45.8 ± 0.3 vol.% and 22.7 ± 0.1 vol.% for the WC-Co-Ni and B4C-Ni MMC coatings, respectively. Flexural tests were used to evaluate the fracture strain of the composites. In these tests, the WC-Co-Ni composite failed by brittle facture at approximately 0.5% nominal strain. The B4C-Ni composite showed flexural behaviour similar to that of an unreinforced Ni matrix. These results suggest that there was insufficient B4C within the coating to affect significantly the ductile failure mode of Ni matrix. Post bending fracture analysis showed the presence of straight, continuous cracks on the WC-Co-Ni surface and the indentation fracture toughness of WC-Co-Ni was found to be 1.2 ± 0.2 MPa·m0.5. Discontinuous, random cracks were observed on the B4C-Ni surface. The quantification of these properties is essential in evaluating the performance of the low-pressure cold sprayings to determine their potential applications.

The aim of this study is to clarify the factors that control the macroscale strength of cold spray coatings by evaluating local strength at the microscale. Using pure copper powder and high-pressure cold spray equipment, thick (15 mm) copper layers were deposited on aluminum substrates. The coatings were evaluated by SEM and EBSD analysis, then freestanding Cu specimens were fabricated in a FIB system, where in-situ micro tensile tests were carried out. The results are presented and discussed along with the role of microvoids.

With the purpose of elaborating high-quality FeAl coatings, a so-called very low pressure reactive plasma spray technique that combines VLPPS and SHS processes was used in the present study. A dense and homogeneous FeAl coating was thus successfully in situ synthesized by reactive plasma spraying of an Al/Fe 2 O 3 composite powder under 1 mbar. The phase composition and microstructural features of the coating were characterized by XRD and SEM. Results indicated that the B2 ordered FeAl phase was synthesized, and the coating featured a dense and defect-free microstructure. The fracture mechanism of the coating remains mainly a brittle failure but the appearance of some dimples in local zones suggests some unexpected toughness.

A successful combination of isolating substrates with conducting metal coatings produced by cold spraying could open new industrial application areas like the fabrication of power electronic components. For minimizing the number of industrial process steps, isolating ceramic layers should ideally be processed by thermal spray techniques. Thus, the present study investigates the impact behaviour and coating formation of ductile metallic feedstock powders onto brittle ceramic coatings. With respect to high electrical conductivity of the metallic lines and good electrical isolation of the ceramic interlayer, copper was cold gas sprayed on previously thermally sprayed Al 2 O 3 coatings. Successful cold coating formation requests different strategies for the activation of the ceramic layer to increase adhesion and to avoid brittle failure. Both can be achieved by applying a bondcoat on the ceramic layer or by using heated substrates during the cold spray process.

In this study, ethylene methacrylic acid copolymer (EMAA) was used as the matrix to produce EMAA/Al2O3 and EMAA/NiCr composite coatings from dry-blended powder mixtures. This work was conducted to determine processing concerns when using similar sized reinforcement particles of different density in a flame-spray process. This work has utility for applications that require a reduction in mechanical wear and/or to confer upon a polymeric deposit a certain functional property by the introduction of value-added powder. Free-standing coatings were produced to test the mechanical properties of the sprayed deposit. The effects of the filler content on the secant modulus, yield stress, and tensile strength are discussed. The differences in deposition efficiencies among the EMAA, Al2O3, and NiCr are highlighted with respect to particle size and density.