Ti60 high-temperature titanium alloys are widely used in the blades and fasteners of aero-engines, which often suffer severe high-temperature fretting damage, leading to crack initiation and reliability reduction. To address the issue, an effort of reliable protective coatings on titanium is essential. Thus, in this work, Ti2AlC-reinforced Ti-based coatings with inhomogeneous microstructure were designed and fabricated by laser direct deposition to enhance the fretting damage resistance and impact toughness. Special attention has been made to the plastic deformation mechanisms under the dynamic impact and high-temperature fretting damage. Results show that a continuous formation of gradient microstructures in α lath size, inner-strain and colony size, which are fabricated by the modulation of the laser energy density along building direction, contributes to a remarkable 170 % increase in the impact absorbed energy and a significant 54 % reduction in the fretting wear rate at 500 °C. Furthermore, the high impact toughness is attributed to the precipitation of α'' martensite and α to β phase transformation during the dynamic impact, which is induced by the high strain rate, activation of dislocations and severe deformation resulting from the inhomogeneous microstructure after the dynamic impact tests. For the anti-fretting damage, a formation of the nanocrystalline layer and plastic deformation layer in the inhomogeneous microstructure coating was detected during the high-temperature fretting. The kink structure generation and nanotwin formation result in the suppression of inner-strain concentration and crack initiation. This work can not only provide valuable insights into the deformation mechanisms of inhomogeneous microstructures under multi-loading conditions of dynamic impact and high-temperature fretting damage, but also offer a new strategy to improve the fretting damage resistance of the high-temperature titanium alloys.
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