Microstructure regulation and performance of titanium alloy coating with Ni interlayer on the surface of mild steel by laser cladding

The preparation of Ti-alloy coating on the steel surface via laser cladding is very easy to form Fe-Ti phase and large tensile residual stress, which is not conducive to the performance of Ti-alloy coating. Here, Ti-6Al-4V coating (TC4-coating) was prepared on the mild steel substrate using laser cladding technology with Ni-alloy as the interlayer, and the Fe-Ti phase inside was completely suppressed. Increasing the powder feeding rate and scanning speed can change the undercooling of the alloy melt and the preferred growth orientation of the grains, while limiting the abnormal grain growth and grain boundary segregation, which is beneficial for grain refinement and equiaxed crystal formation. Reducing the scanning speed and powder feeding rate can increase the molten pool lifetime, thereby increasing the dilution rate of the coating and facilitating the formation of Ti2Ni phase. The abundant Ti2Ni inside the coating gives the TC4-coating greater microhardness (>500 HV0.1) and better corrosion resistance (Icorr of 7.00 × 10−8 A·cm−2). Grain refinement of the coating texture caused by the increase of powder feeding rate and scanning speed, as well as the high content of β-Ti phase and martensite structure, can improve the adhesion and shear strength of TC4-coating (386 ± 31 MPa).