HVAF deposition mechanism of γ-TiAl-based coating containing β phase

The Ti-45Al-7Nb-4V, Ti-45Al-7Nb-4Cr, Ti-45Al-7Nb-2V-2Cr alloy coatings were prepared on the surface of the aluminum alloy by high-velocity-air-fuel (HVAF). The surface and cross-section of three kinds of titanium aluminum alloy coatings and the micromorphology of the bonding interface between the coating and substrate were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The deformation behavior of titanium aluminum alloy particles and the phase composition of the titanium aluminum alloy coating were analyzed by X-Ray Diffraction (XRD) and energy dispersive x-ray analysis (EDAX). The results show that the coordinated deformation between TiAl particles and Al alloy matrix is a necessary condition for the deposition of the first layer of titanium‑aluminum alloy particles. The bonding mechanism of the TiAl coating and the matrix is mechanical bonding, and there are both mechanical bonding and metallurgical bonding between spraying particles. In the process of coating deposition and formation, the β phase grains undergo coordinated deformation to form typical structures such as striped grains and circular columnar crystals. The deformation mechanism of the titanium aluminum alloy particles is the slip and kink mechanism in the grains, and the sliding and rotation mechanism of the grain boundary and the phase boundary. Adiabatic shear instability and dynamic recrystallization occurred during the formation of titanium aluminum alloy coating.