Cold Spraying of Nickel Using High-End Parameter Sets

Even though cold spraying is well established today, the handling of some materials, as for example nickel, is still challenging because of nozzle clogging at higher process gas temperatures. Due to these process limitations in the past, it was not possible to produce coatings of sufficiently high quality. These problems can be solved by new nozzle modifications. By a more effective nozzle cooling system, newly developed at Helmut Schmidt University, the nozzle clogging during cold spraying of Nickel could be avoided. This enables the use of high-end spray conditions, attainable by a modified cold spray gun heating system.

For the presented study, nickel spray powders varying in shape and size were used as feedstock. The coatings were produced with different nozzle types and by varying the spray parameters up to a process gas temperature of 1000 °C at a pressure of 5 MPa with a gas flow of about 160 Nm³, conditions that were not within reach in cold spraying so far. Coating microstructures are almost fully dense, with negligible porosity below 0.1%. The coatings processed under these high-end parameters show high tensile strength of 560 MPa, similar to that of highly deformed bulk material. As well, the corrosion resistance of coatings could be significantly improved over coatings produced using maximum parameters (800°C, 40 bars) of standard spray systems.

In summary, the results demonstrate that the quality of cold-sprayed nickel coatings significantly improves with higher process gas temperatures and pressures, pushing cold spraying to new limits. This may also apply to other high-strength metals and alloys, opening the opportunity to meet the quality requirements for many new applications.