Research On Microstructure And Mechanical Property Of Iron-aluminide Synthesized By Laser Cladding

Iron-aluminide has superior high temperature oxidation and corrosion resistance. Producing iron-aluminide coating on less corrosion resistant carbon steels by laser cladding can significantly improve the corrosion resistance of the material with low costs. The iron-aluminide coatings were in-situ synthesized on Q235 steel by laser cladding. The effect of slagging flux and alloy element (Gr、Ni、Si) on the microstructure and properties of the cladding coatings were studied with the methods of X-ray diffraction (XRD), optical microscopy, scanning electron Microscope (SEM), energy disperse spectroscopy (EDS) and transmission electron microscope (TEM).Aluminum content and slagging flux in the cladding powders have great influence on the microstructure and properties of the cladding coatings. The results indicate that adding slagging flux into the cladding powders not only refines the grains of the cladding layers, but also has a significant influence on the properties of the iron-aluminide coatings. The XRD results show that the main phases of the iron-aluminide coatings are FeAl with B2 phase structure and Fe3Al with DO3 phase structure and the crystallographic orientation relationship between the two phases is Fe3Al(220)//FeAl(101). But the ratio of Fe3Al increases when adding slagging flux. In addition, when adding slagging flux, the iron-aluminide cladding layers shows higher microhardness, better oxidation resistance and better corrosion resistance than those free of slagging flux.Multilayer iron-aluminide coatings consist of bulky columnar crystal and the grain growth is not limited by the thickness of a single layer. The main phases of multilayer iron-aluminide coatings are FeAl with B2 phase structure and Fe3Al with DO3 phase structure, meanwhile there are some small cracks in the coatings. Adding a small quantity of chromium and nickel into the cladding powders can improve the ductility and eliminate cracking of the iron-aluminide coatings. On the contrary, silicon decreases the ductility and increases cracking of the iron-aluminide coatings because of silicon can lead to generating brittle phase Fe3Al0.7 Si0.3. Compared with low carbon steel, the cladding coating has a higher microhardness. Si+Fe+Al coating has the highest microhardness, followed by Ni-Fe-Al coating and Fe+Al coating, Cr+Fe+Al coating has the lowest microhardness. Compared with low carbon steel, the cladding coating has better corrosion resistance. Cr-Fe-Al coating has the best corrosion resistance, followed by Ni+Fe+Al coating, Si-Fe-Al coating has the worst corrosion resistance because of too many cracks.The iron-aluminide coatings were in-situ synthesized on Q235 steel by plasma spraying and laser cladding. The cladding is continuous and smooth, with few defects and excellent bonding with the steel substrate. Combination of the two technologies not only can make the coatings smoother, but also can promote the phase transformation from FeAl with B2 phase structure to Fe3Al with DO3 phase structure. When the aluminum content is 33%, the iron-aluminide coating has no crack and its microhardness is about 360 HV, meanwhile it has the best corrosion resistance. The microstructure and phase structure of the cladding coatings were studied by X-ray diffraction (XRD) and transmission electron microscope (TEM). The results indicate that the phase of the cladding coatings are FeAl with B2 phase structure and with DO3 phase structure.