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

Jun Li,Zhi-shui Yu,Hui-ping Wang,and Man-ping Li School of Materials Engineering,Shanghai University of Engineering Science,Shanghai 201620,China

摘 要：<正>Titanium-based composite coatings reinforced by in situ synthesized TiB and TiC particles were successfully fabricated on Ti6Al4V 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）,scanning electron microscopy（SEM）,and electron probe microanalysis （EPMA）.The results show that the coatings are mainly composed ofα-Ti cellular dendrites and a eutectic transformation product in which a large number of coarse and fine needle-shaped TiB and a few equiaxial TiC particles are homogeneously embedded.A thin dilution zone with a thickness of about 100μm 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 transformation. The microstructural evolution can be divided into four stages:precipitation and growth of primaryβ-Ti phase,formation of the binary eutecticumβ-Ti+TiB,formation of the ternary eutecticumβ-Ti+TiB+TiC,and solid transformation fromβ-Ti toα-Ti.

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