激光熔化沉积Ti6Al4V/Inconel625梯度耐高温涂层组织演变行为研究

Herein, Ti6Al4V/Inconel625 gradient high-temperature resistant coating with dense microstructure, no cracks, holes, and other defects is prepared via laser melting deposition. The microstructure, composition, and phase transformation of the gradient coating are studied via scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Results show the microstructure changes from a lamellar structure comprising lamellar α and β phases to an equiaxed structure with changes in the compositional gradient. Further, as the nickel-based alloy composition increases, the amount of alloying elements and concentration of solute in the liquid molten phase increase. Additionally, when the coating composition is too cold, the nucleation rate increases and the microstructure is further refined. The phase composition of the gradient high-temperature resistant coating changes as follows: α+β → α+β+Ti₂Ni → Ti₂Ni+β → Ti₂Ni+CrNi₂+γ-Ni. β-Ti and Ti₂Ni exist as isolated eutectic phases in the intergranular region, in the presence of a CrNi₂ phase. As the Inconel625 content increases, the hardness of the gradient coating increases. When the volume fraction of the nickel-based alloy reaches 100%, the hardness reaches a peak of 855 HV under the combined action of eutectoid strengthening and solid-solution strengthening. The hardness of the gradient coating is mainly related to the contents of β phase, Ti₂Ni precipitates, CrNi₂ compounds, and solute elements.