Effect of TiC and ZrC additions on microstructure evolution and wear behavior of laser-clad AlNbTiZr coatings on zirconium alloy

In this study, AlNbTiZr-TiC/ZrC composite coatings were fabricated on a Zr-4 alloy surface by laser cladding. The microstructural characteristics of the coatings and their effects on hardness and wear resistance were systematically investigated using X-ray diffraction (XRD), electron channeling contrast (ECC) imaging, electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results show that the AlNbTiZr coating without ceramic addition exhibits a body-centered cubic (BCC) solid solution structure, with a hardness of 313.2 HV, representing an increase of ∼86.7% compared to the substrate (167.8 HV). This improvement is mainly attributed to the solid-solution strengthening effect induced by elements such as Al, Nb, and Ti. After adding TiC, petal-like and rod-like ZrC precipitates are formed, which is associated with TiC decomposition during laser cladding and its subsequent reaction with Zr. In contrast, direct ZrC addition leads to the formation of fine and uniformly dispersed spherical or rod-like ZrC precipitates. The incorporation of TiC and ZrC further increases the hardness of the coatings to 378.6 HV and 430.4 HV, respectively, owing to the combined effects of solid-solution, grain-refinement, and second-phase strengthening. Wear tests reveal that the wear rates of the AlNbTiZr, AlNbTiZr-TiC, and AlNbTiZr-ZrC coatings are reduced by approximately 13%, 21%, and 31%, respectively, compared with the substrate. The results demonstrate that TiC-induced in situ ZrC formation and direct ZrC addition result in distinct microstructural evolution pathways, thereby influencing the strengthening mechanisms and wear behavior of the coatings.