Figure 1 is the microhardness distribution curve of laser cladding composite coating with different components along the depth direction of the bonding zone. It can be seen that the hardness distribution curves of the different composite coatings are similar in the depth direction of the layer, and the microhardness along the matrix, transition zone and the cladding layer are sequentially increased. The microhardness of the cladding layers K1,K2,K3, and K4is 954.8 HV, 967.1 HV, 884.2 HV, 776.2 HV, respectively, which is 2.1 to 2.6 times higher than the matrix(370 HV). The hardness change of cladding layer is mainly caused by the change of different phases in the laser cladding process and the grain refinement due to the rapid heating and cooling of the laser cladding. The new reinforcing phase of the cladding layer can also be used as the core of heterogeneous nucleation during the solidification process of the molten pool, resulting in grain refinement and improving the hardness of the coating. Ni-based alloys contain a large number of Cr elements, which play a role in solid solution strengthening during laser cladding. As shown infigure 1, the hardness of the K1cladding layer without BN is higher, but the hardness distributionfluctuates greatly, which is mainly caused by the high content of TiN reinforcing phase and the uneven distribution in coating. As BN increased to 5%, the hardness of the coating tends to be smooth. This is because the aggregated TiN is decomposed into particles and evenly distributed in the coating. With the addition of BN, the hardness of the coating tends to decrease. Combined with SEM and XRD phase analysis, with the increase of BN mass fraction, theγ-Ni and black coating layered borides increase, and some of the TiN aggregates under the action of the coating layer, and the enhanced phase distribution is uneven, resulting in a decrease in coating hardness.
Figure 1.Microhardness distribution curves of laser cladding composite coatings.
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