To investigate the correlation between the quality and structure of gradient coatings, this study employs laser cladding to fabricate in-situ synthesized Ti(C,N) ceramic phase-reinforced gradient composite coatings on the surface of cast alloy semi-steel substrates, and analyzes microstructure, composition, and properties of the coatings through microstructural characterization and performance testing.

In the experiment, cast alloy semi-steel was used as the substrate. Ni-based NiCrBSi, Fe-based FeCrBSiMo self-fluxing alloy powders, and TiN+C mixed powder (molar ratio 1:1) were used to prepare the coatings via a gradient design. First, a Ni-based transition layer was prepared at a power of 3000–3200 W, a spot diameter of 3 mm, and a scanning speed of 300–400 mm/min. Then, an Fe-based working layer containing 30 % TiN+C was prepared on the transition layer at the same power but a scanning speed of 200–300 mm/min, with Ar protection throughout the process. The coatings were characterized using optical microscopy, scanning electron microscopy, X-ray diffraction, and microhardness testers.

The results showed that sound metallurgical bonding was achieved between all layers. No cracks or pores were observed at the interfaces between the transition layer and the substrate or between the transition layer and the working layer, and an Fe–Ni interdiffusion zone was present, indicating high bonding strength. The Fe-based working layer exhibited an α-Fe cellular dendritic matrix in which in-situ synthesized Ti(C,N) reinforcement phases were uniformly dispersed. These phases showed rhombic, circular, or irregular shapes of varying sizes and existed mainly as Ti(C0.3N0.7). Ti(C,N) was synthesized via an in-situ reaction between Ti produced by TiN thermal decomposition and C and N in the molten pool. Due to the good lattice matching between TiC and TiN, a solid solution combining the advantages of both was ultimately obtained. Hardness tests showed that the coatings exhibited a gradient distribution: the Fe-based working layer had an average hardness of HV_0.2880, the transition layer of about HV_0.2635, and the heat-affected zone of about HV_0.2550. The increase in hardness of the working layer resulted from the combined effects of dispersion strengthening and grain refinement by Ti(C,N), and its network distribution effectively improved wear resistance.

This study confirms the feasibility of fabricating in-situ synthesized Ti(C,N)-reinforced gradient coatings by laser cladding, providing theoretical and technical guidance for the industrial application of laser cladding in surface modification. It is particularly significant for enhancing the wear resistance of components and extending their service life.