Research on microstructure and properties of Ti-based coating prepared by laser cladding on titanium alloy: simulation and experiment

The heat transfer and solidification characteristics significantly affect the solidified microstructure of direct laser deposited coatings. In this work, a Ti-based coating was prepared on the Ti811 alloy by coaxial laser cladding to reveal the in-situ synthesis mechanism of the reinforcing phase and enhance its mechanical properties. The heat transfer evolution and solidification characteristics of the molten pool were investigated by numerical simulations and experiments. The phase composition, microstructure, interface characteristics, nano-hardness, and tribological properties of the deposited coating were studied. The results showed that the sufficient temperature of the molten pool ensured the formation of a deposited coating. The Marangoni convection of the molten pool facilitated the powder particles melting process as well as the uniformity of the reinforcing phase distribution. In addition, the temperature gradient and solidification rate at the upper of the solidified interface increased 2.27 and 29 times, respectively, compared to those at the bottom of the solidified interface. Thermodynamic and simulation results determined the precipitation sequence and mechanism of the phases. Due to the solid solution strengthening, dispersion strengthening effects, and robust interfacial bonding between phases, the nano-hardness of the deposited coating was 2.5 times higher than the substrate. Compared to the Ti811 alloy, the friction coefficient of the coating was reduced by around 30%. The tribological properties of the deposited coating dramatically improved, and the wear mechanism was mainly abrasive wear. This work theoretically and experimentally revealed the primary mechanism of in-situ enhancement to protect titanium alloys.