Preparation Of Corrosion Resistant Nickel-based Coatings By Extreme High Speed Laser Cladding And Performance Study

The strategy of maritime power has become an important development strategy of China.The 20th report of the CPC emphasizes"developing the Marine economy,protecting the Marine ecological environment,and accelerating the building of a maritime power".Advanced offshore equipment is not only a necessary support for the development of Marine blue economy,but also an important guarantee for strengthening Marine national defense forces.With the rapid development of industrialization in our country,higher performance requirement is brought forward for Marine industry equipment metal component in harsh service environment.During service,due to wear,corrosion,fatigue and other reasons,workpiece surface and near-surface parts may fail,which is a major long-term challenge for the reliable service of Marine equipment mechanical moving parts.Therefore,developing anti-corrosion protection coating technology is an urgent need to control the abrasion damage of key mechanical moving parts in the Marine environment,and an essential approach to solve the"bottleneck"problems of high-end Marine equipment systems in our country.Ultra-high speed laser cladding technology can obtain high bonding strength,low dilution rate and high surface quality coating,which is a new technology with great development potential to improve the service life of Marine equipment.Two kinds of nickel-based cladding layers of Q355 steel were studied by ultra-high speed laser cladding technology.NiTi coating prepared by five different laser input powers（2200W,2600W,3000W,3400W,3800W）and Ni-Cr-Mo coating prepared by four different laser input powers（2600W,3000W,3400W,3800W）,respectively.The microstructure,phase composition and corrosion resistance were tested and analyzed.In this paper,the influence of laser power on the temperature field,stress field and deformation of NiTi coating prepared by ultra-high speed laser cladding was predicted by finite element method.For the first time,NiTi coating was synthesized in situ based on ultra-high speed laser cladding technology under high temperature oxidation environment.The wear resistance and corrosion resistance of the coating were comprehensively improved by Ti O₂ formed on the surface.The ultra-high speed laser cladding technology was used to prepare high-quality NiTi coating without cracks and pores.The coating surface was prepared with2600W power to obtain more and dense oxide film,which has the highest resistance.The corrosion potential is-0.448V and the corrosion current density is6.665×10^-6A/cm² in 3.5%Na Cl solution,showing the best wear and corrosion resistance.After annealing treatment,the oxide film on the surface of the coating grows further,the radius of the capacitor arc increases significantly,and the corrosion resistance improves significantly.The experimental results of ultra-high speed laser cladding Ni-Cr-Mo coating in this study show that the four groups of samples have the same phase composition,which is composed ofγ-Ni solid solution with Cr and Mo Ni₄ isophase.With the increase of laser input power,the corrosion resistance of the coating increases first and then decreases.The coating prepared with 3000W power has the maximum impedance,and the corrosion potential is-0.376V and the corrosion current density is 6.701×10^-6A/cm² in3.5%Na Cl solution,showing the best corrosion resistance.In order to further improve the corrosion resistance of Ni-Cr-Mo coating,Ca F₂ doping was applied to the coating.After doping,the corrosion potential of ultra-high speed laser cladding Ni-Cr-Mo coating reached-0.174V,the corrosion current density was5.219×10^-8A/cm²,and the corrosion and wear resistance of the coating was further improved.