| Because of its advantages, laser cladding technique has been widely used in the field of aviation, aerospace, mould, automotive, and so on. For example, laser cladding can produce the dense coatings with a metallurgical bond to the substrate, where the small heat-affected-zone(HAZ) is generated. Moreover, the processing operation is easy to realize the mechanization and automatization. The cladding materials include Ni-, Co- and Fe-based alloy powder as well as the ceramic-metal composite powder. Especially, Fe-based alloy powder with good performances, such as the similar composition as steel, good wettability, and high bond strength, has a perspective application in industry. Although Fe-based alloy powder has a relatively low price, the successive Fe-based coatings by laser cladding have low hardness and poor wear resistance. According to the liquid phase separation in Fe-Cu alloy, laser cladding is adopted to prepare Cup reinforced Fe-based composite coatings on the surface of A3 steel plate. The structure(macro & micro) were analyzed by an optical microscope(OM), a scanning electronic microscope(SEM) and an X-ray diffraction(XRD). Additionally, the microstructure evolution and properties of coatings(micro-hardness, corrosion resistance and crack sensitivity) are also investigated. The main results are listed as follows:When the laser scanning speed increases and other processing parameters remain unchanged, the width and height of single-track Cup reinforced Fe-based composite coating reduce and the dilution has little change. When the laser power increase, the cladding width has little change but the cladding height increases. Moreover, the optimized parameters for multi-track Cup reinforced Fe-based composite coatings by laser cladding are also obtained: the laser power 2 kW, the powder feeding rate 10 g/min, the spot diameter 5.0 mm, the laser scanning speed 8 mm/s and the overlapping rate 40%.The Cup reinforced Fe-based composite coatings by laser cladding consist of α-Fe and ε-Cu. The demixing phenomenon occurs in the coatings, which are composed of Fe-rich layer at the bottom and of Cu-rich layer at the top. Due to the liquid separation in Cu-Fe alloy, the spherical Cu-rich particles are dispersed in the Fe-rich matrix at the bottom of coating, while the spherical Fe-rich particles were embedded in the Cu-rich matrix at the top of coating structure. It is found that the secondary phase-separation occurs in the precipitated particles. In addition, the Fe-rich layer has a characteristic of the directional solidification. The microstructure of coating is characterized by the planar growth, cellular crystals, dendrites and equiaxed crystals. With increasing the laser scanning speed, the grain of Fe-rich matrix becomes fine, and Cu-rich particles decreases in size and distributed dispersedly. However, when the laser scanning speed is increased to 12 mm/s, Cu-rich particles with different sizes are precipitated in the coatings.The corrosive behavior of coatings is relevant to the cooper content, the laser scanning speed and the surface quality of coatings. With the increasing of cooper content, the corrosive behavior of coatings increases.The microhardness of coatings increases with the increasing of the laser scanning speed, whose strengthening mechanisms are the combination of solid-solution strengthening, second-phase strengthening, dispersion-strengthening, and fine grains strengthening. When the laser scanning speed is 12 mm/s, porosities and cracks can be observed in the multi-track Cu20Fe80 and Cu35Fe65 composite coatings. To improve the crack sensitivity of coatings, Cu-rich or Fe-rich particles with uniform size and homogeneous distribution should be obtained, and the temperature gradient between the coatings and the substrate should be decreased. |
