The excellent corrosion resistance and biocompatibility of titanium make of it the material to choose for biomedical applications. Cold spraying, as a new coating technique, can be used to deposit protective Ti coatings onto less performing materials such as stainless steel and Co-Cr alloys, commonly used for biomedical implants. In addition, Cold Spray has the advantage, in comparison with conventional thermal spray techniques, to permit the deposition of oxygen-sensitive materials. In this study, Cold Sprayed Ti coatings were prepared on Co-Cr alloy substrates by using different spray process conditions. The microstructure of coatings was observed by SEM and the inner porosity was estimated by image analysis. Oxygen and nitrogen contents were investigated on a set of free standing deposits obtained using different process parameters. In the same way, the roughness and microhardness of deposits, such as the adhesion strength with the substrate, were measured. Finally, the corrosion performance of the coatings was evaluated by mean of open circuit potential measurement (OCP) and potentiodynamic polarizations scans. The electrochemical response was therefore discussed and compared to the corrosion behaviour of the Co-Cr alloy substrate and the bulk Titanium.

The processes of microstructural evolution in titanium during deposition by cold spray were investigated. Titanium particles underwent plastic deformation at very high strain rates, resulting in (a) extensive refinement and (b) large inhomogeneities in microstructure. There were large nanostructured areas (several micrometres in extent) with high dislocation densities and subgrain sizes less than 100 nm. Dense dislocation tangles and elongated subgrains were observed in other places. It is hoped that by further understanding the microstructural changes that occur during cold spray, improvements in mechanical properties may be realised.

Titanium and titanium alloy coatings have high potential for applications in several industrial fields such as aerospace, bio-medical and chemical industries. Its eligibility for each single application depends on physical, chemical and mechanical properties. Cold spray as a deposition technique for titanium coating is growing because there is no need for vacuum or protective atmospheres. The properties of cold spray titanium coatings can be tailored by controlling and optimizing the process parameters. In this study the effect of the gas pressure and temperature on the deposition process and the coatings properties were examined. Cold spray CP-titanium coatings were produced using nitrogen as propellant gas at different gas pressures (from 2.0 MPa to 3.5 MPa) and temperatures (from 400°C to 800°C). Morphology and the microstructure of the CP titanium powder and coatings were studied by scanning electron microscope (SEM) and light optical microscope (LOM). Micro-hardness measurements and oxygen and nitrogen contents of titanium powder and the coatings were performed. As a final step, residual stress analysis of deposits were measured by means of X-ray diffraction.

This study investigates microstructural alterations in copper powder during cold spraying. A highly nonhomogeneous structure was observed with average strains of almost 50% close to the interface. Large strains and high strain rates resulted in significant grain refinement and the formation of sub 100-nm grains. Deformation occurred by slip and twinning, the latter promoted by impurities in the copper feedstock. Thin foils from the deposits were studied by TEM analysis and cross-sections of deformed particles were made and examined using FIB-SEM techniques.

Titanium is widely used in aerospace, highly corrosive environments and implants due to unique properties such as high strength to weight ratio and excellent corrosion resistance. Cold gas dynamic spray (cold spray) technology in contrast to current fabrication technologies has provided the potential for titanium to be utilised in broader industrial applications and at lower cost. Particle velocity is the most important parameter in cold spray process that leads to successful deposition of titanium at supersonic speeds. In this study, particle image velocimetry (PIV) is used to determine particle velocities for a commercially pure (CP) titanium powder in respect to cold spray parameters such as temperature and pressure. The results show the significance of flow field measurements using PIV in optimization of the nozzle configuration to achieve the maximum velocity for particles. Further more, PIV results can be used to validate the current models developed for cold spray process.

Copper particles with median diameter 15.2 micrometres were cold sprayed onto a polished aluminium 1139 substrate. Under the spray conditions used, deep embedment of the copper particles occurred. The as-sprayed copper particles were dissected using a focussed ion beam (FIB), and their microstructure investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At the crater wall an intense shear zone developed due to sliding of copper past aluminium. Evidence of melting is presented.