Study On Microstructure And Properties Of Laser Cladding Nano Ceramic Reinforced Nickel-based Composite Coatings

Corrosion, which usually begins with the surface of the work-piece, is an important factor leading to the damage or failure of the equipment under high temperature and pressure or corrosive medium environment. Using laser cladding technology to prepare corrosion resistant cladding layer on steel structure surface is one of the effective methods to solve this problem. In this paper, Ni60A laser cladding layer, Ni60A+nano-Al2O3composite laser cladding layer, laser re-melting thermal spraying pure aluminum coating and laser re-melting thermal spraying pure aluminum coating+(Ni60A+12%nano-Al2O3) composite coating were prepared on Q345R steel surface by laser cladding, the technological parameters of laser processing was optimized, the microstructure and corrosion resistance of cladding layer and re-melting coating were studied.The Study showed that with the laser power of2500W, circular light spot diameter of4mm, scanning speed of5mm/s, Ar gas flow of15L/min, preset powder thickness of1mm, and overlapping ratio of25%, the surface quality and properties of Ni60A cladding layer was best. The best laser power for preparing Ni60A+nano-Al2O3laser cladding layer and laser re-melting thermal spraying pure aluminum coating were2200W and1200W respectively, without any change to other parameters mentioned above.Ni60A cladding layer was mainly composed of dendrite crystal and carbide and boride eutectic structure which were banded and massive, and its main phase were y-(Ni,Fe), CrB, Ni3B, M23C6and M7C3. In Ni60A+nano-Al2O3composite cladding layer, with the increase of nano-Al2O3content, cladding layer microstructure was obviously refined and composition was tended to be more uniform. There are Ni3Al, Al13Cr2, AlCr3B4, AlB2, Al82Fe18phase in the layer, but no obvious Al2O3phase appeared. Before laser re-melting, there is only Al elemental phase in the thermal spraying pure aluminum coating, however, the coating microstructure phase obviously turned into Fe3Al and FeAl phase after that. Meanwhile, the coating microstructure turn from intertwined, stacked spray particles into homogeneous iron and aluminum inter-metallic compound. After laser re-melting, the main phase in composite coating of Ni60A+nano-Al2O3composite powder were y-(Ni,Cr,Fe), Ni3Al, Ni3Fe3B2, CrFeC0.45, etc., which proved that nano-Al2O3decomposed in the re-melting process, and Al element in the former coating reacted with other elements and transmitted to the cladding layer.Each coating corrosion resistance was studied by electrochemical corrosion test and immersion corrosion test. The corrosion resistance of pure Ni60A laser cladding layer was much better than Q345R steel, but worse than Ni60A+nano-Al2O3cladding layer. When the adding amount of nano-Al2O3is limited in12%, with the increase of nano-Al2O3, the corrosion resistances of composite cladding layers increase gradually. But the corrosion resistance was on the decline after adding15%or more nano-Al2O3. Thus, it can be concluded that the best corrosion resistance coating was cladding layer adding12%nano-Al2O3. Besides, the corrosion resistance of pure aluminum coating decreased after laser re-melting. However, after laser re-melting, the electrochemical corrosion resistance and immersion corrosion resistance of coating made by Ni60A+nano-Al2O3composite powder on the surface of spraying pure aluminum coating, were improved significantly, which was benefitted from fine-grain strengthening and solid solution strengthening effect of nano-particles.