Microstructure and Mechanism of Ti2AlNb/TiC+Ti3SiC2 Gradient Materials by In-situ Reaction Laser Cladding

The Ti connecting layer-Ti+SiC transition layer-ceramic composite layers structure is designed and the Ti2AlNb/TiC+ Ti3SiC2 system gradient material is successfully fabricated by in-situ reaction laser cladding. The microstructures of different layers are analyzed by scanning electron microscope(SEM), energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD). The results show that the interlayer bonding is fine and the gradient transition in the composition and the microstructure is realized. The gradient material consists of six composite layers and the total thickness is 1.5 mm. In the Ti+SiC transition layers, Ti and SiC react to produce TiC and Ti5Si3, and some Ti-rich phases are retained in the layers. In the ceramic composite layers, Ti, Si and C react to form Ti5Si3, TiC and Ti3SiC2. The microhardness gradually increases from the matrix, to the Ti connecting layer, the Ti+SiC transition layer and to the ceramic composite layer. The maximum value is 1 341 HV. The ternary Ti3SiC2 in the outermost layer exhibits the evidently lower microhardness than TiC and Ti5Si3, which leads to a slight decrease in the microhardness of the composite layer. The fabricated gradient materials should exhibit superior heat-resistance due to the presence of refractory TiC, Ti5Si3 and Ti3SiC2.