Cold-Spraying of Ti2AlC MAX-Phase Coatings

Cold spraying has been applied to deposit Ti₂AlC on different substrate materials. The study of single impacts by scanning electron microscopy indicates that bonding of the first layer is mainly attributed to the deformation and shear instabilities of the substrates. Nevertheless, the irregularly shaped particles flatten by the impact. This deformation appears to be attributed to local, internal shear, but also to internal fracture.

By applying up to five passes under more sophisticated spray parameters, Ti₂AlC - coatings with thicknesses of about 50 to 80 µm can be achieved. Coatings analysis was performed by optical microscopy, scanning electron microscopy and X-ray diffraction. XRD analysis of the coating proves that the crystallographic structure of the feedstock can be retained during cold spraying. The coating microstructures show rather low porosity, but several cracks between spray layers. Successful build-up of more than one monolayer can probably be attributed to internal deformation and occurring shear instabilities within the highly anisotropic Ti₂AlC – phase. The final coating is textured, which is probably due to distinct gliding systems of the nano-laminated MAX powder.

So far, attainable properties of cold sprayed MAX coatings are still strongly influenced by defects, in particular cracks. Further experiments are under investigation to improve coating microstructures and performance. Nevertheless, the first successful deposition of MAX–phases by cold spraying is very encouraging in view of applications.