A Novel Amorphous Alloy Coating for Elevating Corrosion Resistance of X70 Pipeline Steel

In the current investigation, X70 pipeline steel plate was welded using submerged-arc welding. Thereafter, a (Fe_0.5Ni_0.2)₆₁Cr₉Co₆Si_1.5B_17.5Nb₅ amorphous alloy coating with a thickness of 400 ± 30 μm was successfully deposited on the surface of welded X70 pipeline steel by high velocity oxy-fuel (HVOF). The corrosion resistance of the substrate and coating in acidic environments was discussed, and the corrosion mechanisms were analyzed. The results show that the coating is completely amorphous with a dense microstructure, showing a typical thermal spray laminar flow-like structure. The corrosion potential (E_corr) and self-corrosion current density (I_corr) are − 396 mV and 2.061 × 10⁻⁶ A/cm², respectively. The E_corr of all coatings is better than that of substrate. The coating A, where the BM zone is located, has the largest capacitance resistance arc radius and the smallest I_corr (1.427 × 10⁻⁷ A/cm²), which provides the best corrosion resistance. The maximum I_corr of the coating (I_corr = 2.320 × 10⁻⁷ A/cm²) is one order of magnitude lower than the minimum I_corr of the substrate (I_corr = 2.061 × 10⁻⁶ A/cm²), which indicates that the coating has better corrosion resistance than the substrate. The corrosion mechanism of the coating in H₂SO₄ solution is active dissolution of metal elements in the coating (initial stage) and passivation film protection coating (later stage). This work provides a very valuable idea to solve the problem of corrosion failure of X70 pipeline steel.