Alexander List

Single Impact Bonding of Cold Sprayed Ti-6Al-4V Powders on Different Substrates

The objective of this study is to investigate particle deformation and bonding over a wide range of impact conditions, cold spraying of spherical Ti-6Al-4V powders was carried out with nitrogen as process gas onto titanium grade II, Ti-6Al-4V, and aluminum and magnesium alloy substrates. The bond strength was assessed by applying a modified cavitation test. The corresponding impact morphologies and fracture morphologies, as obtained after cavitation testing, were studied by scanning electron microscopy. The investigations demonstrate that bonding and adhesion of spherical Ti-6Al-4V particles depend strongly on substrate properties. Higher bond strength is achieved for material combinations that show lower differences in properties (density, hardness, thermal and mechanical properties), e.g., in the case of Ti-6Al-4V on Ti and Ti-6Al-4V substrates. This is attributed to more pronounced formation of adiabatic shear instabilities for more compatible material combinations.

Cold Spraying of Amorphous Cu50Zr50 Alloys

A new range of applications in cold spraying is expected for bulk metallic glass (BMG) coatings. For retaining amorphous structures in cast multi-component BMG parts, typically high purity raw material must be used. The present investigation explores an alternative approach, where cold spraying is used to deposit a technical-grade binary amorphous alloy. This approach is shown to be potentially cost-effective and suitable for rapid manufacturing. For this purpose, amorphous Cu50Zr50 was chosen as a model alloy system, and cold spraying was performed using nitrogen as process gas. By a systematic variation of the spray parameter sets, the critical velocities for coating formation were determined experimentally. Based on the current models of bonding of amorphous Cu50Zr50 powder in cold spraying, a new, more comprehensive concept of bonding and rebound is presented, which also considers the presence of liquefied interfaces and quenching rates for resolidification. Results concerning impact morphologies and coating formation demonstrate that under suitable choice of spray conditions, well-adhering coatings with amorphous structure of the Cu50Zr50 powders can be obtained by cold spraying.

Coating formation, fracture mode and cavitation performance of Fe40Al deposited by cold gas spraying

The present study investigates the coating formation by cold spraying Fe–40 at.-%Al intermetallics and evaluates their cavitation performance. Coating properties identify them as good candidates for application in many industrial environments. Despite their low ductility, after optimising the spraying parameters, dense layers were achieved. Fracture surfaces after bending tests indicate a combination of ductile and brittle failure, revealing some information on bonding features. The high microstructural homogeneity of these coatings, similar to that of bulk materials, is beneficial for their resistance to cavitation damage. The high strength of cold sprayed intermetallics makes them an interesting alternative to other materials and coating solutions.