Microstructures and tribological properties of laser-clad FeCrAl-TiX composite coatings on ferritic-martensitic steel

Abstract

To enhance the surface performance of ferritic-martensitic (FM) steel for potential nuclear application, three defect-free FeCrAl-TiX composite coatings (namely FeCrAl–TiC, FeCrAl–TiN, and FeCrAl–TiB₂) were fabricated on a typical FM steel by employing laser cladding. Various characterization techniques were jointly used to meticulously examine the microstructures of these coatings, which were then correlated with their hardnesses and tribological properties. Results indicate that the cladding zones (coatings) of all laser-clad specimens primarily consist of finely equiaxed grains. The FeCrAl–TiC and the FeCrAl–TiB₂ coatings have grain sizes of 2.0 ± 1.3 μm and 1.5 ± 0.6 μm, respectively, smaller than that of the FeCrAl–TiN coating (2.9 ± 1.5 μm). The TiC, TiN, and TiB₂ particles added into the premixed powders are dissolved during the laser cladding and then re-precipitate as fine granular TiC, strip-like and petal-like TiN, granular TiB₂ and net-like Cr₂B₃ compounds in these coatings, respectively. The heat-affected zones of all three laser-clad specimens primarily consist of fine martensitic laths and a small number of blocky ferrites, with a thickness of approximately 85–95 μm. The wear rates of the FeCrAl–TiC, FeCrAl–TiN, and FeCrAl–TiB₂ coatings are determined to be 0.7 × 10⁻⁵ mm³ N⁻¹ m⁻¹, 2.5 × 10⁻⁴ mm³ N⁻¹ m⁻¹, and 1.2 × 10⁻⁵ mm³ N⁻¹ m⁻¹, respectively. Notably, the FeCrAl–TiC and the FeCrAl–TiB₂ coatings have wear rates much lower than the substrate (2.9 × 10⁻⁴ mm³ N⁻¹ m⁻¹), indicating significantly enhanced wear resistance. Comprehensive analyses reveal that their superior tribological performances could be ascribed to synergistic effects of multiple hardening/strengthening mechanisms resulting from adding TiC and TiB₂ ceramic particles.