Effect of Ti content on microstructure evolution and properties of Ni50A-B4C coatings

Ni50A-B₄C-Ti coatings with varying Ti contents (0–6 wt.%) were fabricated on H13 steel via laser cladding technology, and the effects of Ti content on the phase composition, microstructure, properties of the coatings, and microstructure evolution were systematically investigated. Results indicate that the introduction of Ti promotes the formation of TiC and TiB₂ phases and increases the lattice constant of the FeNi phase (from 0.17855 nm to 0.17975 nm), attributed to the solid solution strengthening effect caused by the larger atomic radius of Ti (132 p.m.). Microstructural analysis reveals that the addition of 1 wt% Ti generates submicron TiC particles (0.17–0.2 μm) pinned within lamellar precipitates, significantly enhancing the hardness (659.83 HV_0.5) and wear resistance (wear loss of 1 mg). However, when Ti content increases to 6 wt%, TiC/TiB₂ eutectic structures form through a preferential precipitation mechanism, while the exothermic nature of in situ reactions induces microstructural coarsening, leading to a hardness reduction (415.83 HV_0.5). Electrochemical tests demonstrate that the 6 wt% Ti coating exhibits optimal corrosion resistance, characterized by the lowest corrosion current density (I_corr), which is attributed to the high compactness and self-healing capability of the TiO₂-Cr₂O₃ composite passive film. The study demonstrates that moderate Ti addition (1 wt%) optimizes mechanical performance, whereas higher Ti content (6 wt%) significantly improves corrosion resistance, providing a theoretical foundation for the composition design and performance regulation of laser-clad coatings.