Microstructural evolution of titanium matrix composite coatings reinforced by in situ synthesized TiB and TiC by laser cladding

Titanium-based composite coatings reinforced by in situ synthesized TiB and TiC particles were successfully fabricated on Ti6AI4V by laser cladding using Ti-B4C-Al or Ti-B4C-C-Al powders as the precursor materials. The microstructural and metallographic analyses were made by X-ray diffraction (XRD), optical microscope (OM), manning electron microscopy (SEM), and electron probe micro-analysis (EPMA). The results show that the coatings are mainly composed of ot-Ti cellular dendrites and a eutecfic transformation product in which a large number of coarse and fime needle-shaped TiB and a few equiaxial TiC particles are homogeneously embedded. A thin dilution zone with a thickness of about 100 μm is present at the interface, and it consists of a few TiB and TiC reinforcements and a large number of lamella grains growing parallel to the heat flux direction in which a thin needle-shaped microstructure exists due to the martensitic transfor-marion. The mierostructural evolution can be divided into four stages: precipitation and growth of primary β-Ti phase, formation of the binary eutecticum β-Ti+TiB,formation of the ternary eutecticum β-TiB+TiC,and solid transformation from β-Ti to -ti.