Laser-power-regulated microstructure, tribological performance, and corrosion resistance of Bi-In-Sn/TiN coatings fabricated by laser cladding nitriding

Bi-In-Sn/TiN composite protective coatings were fabricated on Ti6Al4V by laser cladding nitriding under different laser powers to clarify the power-dependent evolution of microstructure, tribological behavior, and corrosion performance. XRD analysis confirmed TiN, α-Ti, BiIn, and BiSn as the principal phases. Raising the laser power enhanced the nitriding reaction and promoted the development of TiN from relatively fine and isolated structures into well-developed dendritic and needle-like morphologies. However, excessive thermal input intensified the loss of the low-melting-point Bi-In-Sn constituent. At 1200 W, a relatively uniform coating without obvious continuous cracks was obtained, together with favorable migration and retention of the lubricating phase. Further increasing the power enhanced TiN growth but increased cracking susceptibility and Bi-In-Sn loss. The peak hardness rose from approximately 670 HV 0.5 at 1000 W to 1010 HV 0.5 at 1600 W. The tribological responses showed different power dependences: the minimum average friction coefficient was 0.31 at 1200 W, 39.2 % below that of the Ti6Al4V substrate, whereas the lowest wear rate, 1.18 × 10⁻⁶ mm 3 ·N⁻ 1 ·m⁻ 1 , was obtained at 1600 W, corresponding to a reduction of 66.8 %. Electrochemical measurements identified 1200 W as the most favorable condition for corrosion protection, giving a charge-transfer resistance approximately 5.8 times that of the substrate and a corrosion current density of 2.02 μA·cm⁻ 2 , representing a 43.1 % reduction. These results demonstrate that laser power governs the trade-off among TiN strengthening, Bi-In-Sn lubrication, and corrosion protection, leading to distinct optimum conditions for friction reduction and wear resistance.