83 / 2021-06-30 15:57:06

Effect of multiple alloying on microstructure and abrasion resistance of laser cladding nickel-based alloy coatings

Nickel-based coating; Laser cladding; Corrosion; Multielement alloy

In Marine engineering, a large number of parts, such as fasteners, pump bodies, valves and components of seawater desalination plants, work under harsh environments such as corrosion and erosion. The fabrication of nickel-based coating on the surface can effectively improve its seawater corrosion resistance. Nickel-based alloys have face-centered cubic (FCC) structure. It has excellent metallurgical compatibility with other alloy elements such as Cr, Mo and Fe in crystallography. The addition of Al has an important effect on the corrosion resistance and mechanical properties of the alloys. By referring to a large number of literatures at home and abroad, Ni-Cr series alloys were selected to improve the performance by adding alloying elements Mo and Al. Two alloy systems, NiCrMo and NiCrMoAl, were designed and the coatings were fabricated by laser cladding. The phase and microstructure evolution of the coating were studied, the corrosion resistance and corrosion mechanism of the coating in chlorine-containing solution were analyzed, and the effects of the addition and content of Mo and Al alloying elements on its corrosion properties were discussed. This research is helpful for the development of the corrosion resistant coatings of marine engineering equipment and provides effective theoretical and experimental support for their performance improvement.

The results show that with the increase of Cr content in NiCrxMoy coatings (x value increases from 1 to 1.5), the coating phase changes from a single FCC to FCC+BCC dual phase structure. The increase of Mo content (Y value) in coating promotes the precipitation of σ phase. NiCr1.5Mo0.1 coating surface formed a passivation film containing higher Cr³⁺ and Mo⁶⁺ ions, which slowed down the corrosion of the coating and showed the best corrosion resistance. The addition of Mo element increases the coating passivation range (ΔE) and enhanced the pitting corrosion resistance. The addition of Al element changed the phase of NiCrMo coating from FCC to BCC. In Alx(NiCrMo0.1) coating, the addition of Al reduced the corrosion resistance of NiCrMo0.1 coating, while in Alx(NiCrMo0.3) coating, the addition of appropriate Al improved the corrosion resistance of NiCrMo0.3 coating. The main mechanism of coating corrosion is the galvanic corrosion caused by the increase of grain boundary and the component segregation. After the addition of Al element, the appearance of BCC phase and the lattice distortion caused by the solid solution of Al with large atomic radius lead to phase transition and solid solution enhancement, thus enhancing the microhardness of the coating.