Microstructural evolution and anti-corrosion properties of laser cladded Ti based coating on Q235 steel

Titanium (Ti) based coatings laser cladded on steels could effectively protect steels from corrosion in the marine environment. However, the microstructural evolution and underlying solidification mechanisms for Ti based coatings laser cladded on steels are still unclear due to the nonequilibrium solidification processes during laser cladding. In this study, a Ti based coating was prepared on a Q235 steel by laser cladding. The microstructural evolution and corrosion properties of the coating were systematically investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), electron probe micro-analysis (EPMA) and electrochemical measurements in 3.5 wt% NaCl solution. Four typical regions form in the Ti based coating and the constituent phases evolve from alpha-Fe + TiFe2 phases to TiFe2 phase, then to TiFe phase, and finally to Fe0.2Ti0.8 (metastable beta-Ti) + TiFe + Ti2Fe phases from the fusion interface to the coating surface. Temperature gradients and solidification rates determine the microstructure morphologies of the Ti based coating, and the contents of Fe in the Ti based coating evolve and affect the phase transformations at different distances from the fusion interface. Moreover, the Ti based coating shows better anti-corrosion properties than the substrate. The effect of microstrain at different regions on the microhardness and corrosion properties is also discussed. This study can be the base of optimizing the microstructure of laser cladded Ti based coatings on steels for better corrosion performances.