| Abstract: |
The nanoscale features of a dense pure titanium coating obtained by Cold Gas Spraying onto an aluminium 7075-T6 substrate were investigated in order to enlighten some controversy that exists concerning the bonding mechanisms. Whether the so called adiabatic shear instabilities or the mechanical interlocking is the most dominant is not still clear and it rather seems to depend on the coating-substrate pair.
In the present case, the Transmission Electron Microscopy results reveal a nanostructure containing elongated large grains with crystallite size around a few micrometers, which coexist with more equiaxed grains. The occurrence of those elongated grains would be in agreement to the model of the adiabatic shear instabilities phenomena, where upon impact, within the contact region near the interface, the grains are highly deformed. An important amount of dislocation cells are created as well as subgrains, which were also observed by TEM. Furthermore, a slightly gradual compositional change along the interface as well as a non-sharp hardness transition would confirm that titanium is bonding thanks to a thermal softening rather than interfacial instabilities.
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