The cold gas dynamic spray process offers a unique advantage to form composite coatings by applying powder mixtures. The powder mixture constituents are supposed to interact with each other during impact. In this study, Al and Cu-based powder mixtures are used with the aim to define specific features of the coating formation. Composite coatings with different Al 2 O 3 , SiC, and Ti content are sprayed. Impact behavior of various powder mixtures is analyzed based on scanning electron microscopy images. The Al 2 O 3 and SiC phases of the initial powder are found to be fractured on impact and preserved in the coatings. Another advantage of the kinetic spray process is the ability to mix materials which would normally react with each other and form a composite coating. Some experimental data of such reactions are discussed. Within the composite coating, each constituent changes the initial properties of the sprayed powder material: for example, the soft matrix is strengthened, and hard particles are fractured. The fracture and deformation behavior of the particles and their reactions induced by the impact are determined by micromechanical tests and EDX analysis. Morphology, physical and mechanical properties of the sprayed coatings are discussed.

Spraying metal-ceramic coatings is a complicated task because, in addition to the spray parameters of the metal particles, it is necessary to take into account those of ceramics. This paper presents some results concerning the effect of the nature, particle size, and velocity of ceramics on the metal-ceramic coating properties. Copper and aluminium powders are used as metal components. Two fractions (fine and coarse) of aluminium oxide and silicon carbide are sprayed in the tests. Ceramic particle velocity is varied by the particle injection into different zones of the gas flow: in the subsonic (pre-chamber) and supersonic parts of the nozzle, and in the free jet after the nozzle exit. Simulation results and measurements of the particle velocity by the track method are compared. Influence of the ceramic particle parameters on the coating formation process and its properties is discussed.

This paper presents some results of investigation of the cold spraying various composites including metal-ceramics, metal-metal with a new nozzle design. The objective of this study was to develop a nozzle with an ejector that allows the injection of powder components in different points of the gas flow that can provide optimal spray parameters for each component. For this purpose the installation was equipped with three feeders and three powder feed ports. The first one was located in a pre-chamber (high pressure powder feeder) and two others were located in the ejector in supersonic part of the nozzle. Varying the powder injection location of any component allowed us to change the spray parameters of the mixture. Some preliminary spray results of different powder mixtures are presented to illustrate possibilities of such approach. It is shown that an addition of ceramic or metal powder to the sprayed metal can significantly change the spray process and coating characteristics

The response of Ni-SiC powders deposited by Gas Dynamic Spraying (GDS) with various particle velocities, and their compaction behavior to the different packing densities were studied in parallel. Bulk compacts (90–99% dense), made in the form of 6 mm diameter by 3 mm thick disks, were analyzed to determine the structural changes occurring within the particles and at the particle boundaries, and to examine their mechanical properties. Optical microscopy and SEM observations revealed the presence of a lamellar morphology and a strong interparticle bonding in the composite coating. An analysis of the experimental data revealed the retention of the nanoscale structure and a localized grain refinement. Adiabatic shear band areas were observed and thought to be responsible for the grain refinement. Powder layers, which were shear compacted to the packing density (up to 90% dense), showed the best densification characteristics. Correspondingly, coatings with enhanced mechanical properties and a strong exchange coupling between hard and soft phases are obtained.

In this paper, three goals are attacked, namely synthesis of nanostructured hydroxyapatite (HA) powder, obtaining HA phase constitution close to that of the bone hydroxyapatite, and preserving the initial HA composition and crystal structure in the sprayed coating. HA-aluminum composite coatings are produced using the cold gas dynamic spray method (CGDS). It is observed that the CGDS process enables the application of coatings without changing the phase composition of the HA, whereby the HA biocompatibility is retained. Paper includes a German-language abstract.

In an emerging thermal spray process a coating is formed by exposing a metallic or dielectric substrate to a high-velocity jet of solid-phase particles, which have been accelerated by a supersonic gas jet at a temperature much lower than the melting or softening temperature of the particle material. This is known as "Cold Gas-Dynamic Spray" (CGDS) method. Using this method, 2618 Al substrates were coated with nickel-aluminum bronze powders (~100 and ~400 mesh) in an effort to obtain improved wear resistance. The coatings have been examined for their microstructure, hardness, and bond strength. Triple lug shear tests performed on coated panels provided quantitative measurement of the coating/substrate interfacial shear strength. The steady state wear rates were determined using the pin-on-rotating ring test at a pressure of 690 kPa and a sliding velocity of 9 m/s. The wear resistance of the nickel-aluminum bronze coatings is discussed in conjunction with scanning electron microscopy (SEM) examination of the wear tracks and metallography of the polished transverse cross-sections. Though the coatings are not completely free from porosity, they exhibit high interfacial shear strength and wear resistance due to the low-temperature, ballistic impingement of the powders in the cold gas-dynamic spray method. The ~400 mesh powder coating shows higher interfacial shear strength and wear resistance in comparison with the ~100 mesh powder coating.