Research On Microstrure And Properties Of Metal Ceramic Composite Coating By Laser Cladding

The fabrication of metal ceramic composite coating on titanium alloy surface by lasercladding could achieve the good combination of the excellent properties of the metal matrixand the ceramic. The application prospect of this research field is wide at present. Coating thatis mainly composed of Ni metal matrix and a great deal of ceramic phases of Ti₅Si₃ isfabricated on the Ti-5621s titanium alloy surface by laser cladding with optimal laserparameters. Coating that is mainly composed of Ni metal matrix and a great deal of ceramicphases of TiC is fabricated on the Ti6A14V titanium alloy surface. The composition,microstructure and hardness of cladding layers were system studied by EMPA, SEM andXRD. The dependence of micro-hardness on depth is studied.Composite coating with different coating compositions are fabricated on the titaniumalloy surface by laser cladding with optimal laser parameters. Ni-Cr-Si-Co (SA) compositecoating is mainly composed of Ni metal matrix and a great deal of stable phases of Cr₃Si andNi₄Ti₃ and metastable phases of Cr₂Ti. Ni-Cr-Si (SB) composite coating is mainly composedof Ni and Cr metal matrix and a great deal of stable phases of Ti₅Si₃ and Cr₃Si and metastablephases of Ni₄Si₃ and Cr₃Si. Ni-Cr-Si-B (SC) composite coating is mainly composed of Nimetal matrix and a great deal of stable phases of Ti₅Si₃,Cr₂B,Ni₃B and TiB₂ and metastablephases of TiB. Ni-Cr-Ni-C (SD) composite coating is mainly composed of Ni metal matrixand a great deal of stable ceramic phases of TiC. They exist in the coatings melting zone withthe state of the advanced eutectic metal matrix in the dendrites and eutectic mixture inintergranular. High density dislocation pile-up lies in the interface of the matrix and thesecond phase, which induce the sub-structure fining of the metal matrix. The output of thein-situ product varies with the content of the coating composition.Cladding layers under different cladding parameters were carried out in order to get thebetter performance of cladding layers. For example, with the same cladding powders, thecladding powers were different; with the same cladding power, the powders were different.The result shows that the optimal laser parameters must be choose so that we can get the goodperformance cladding layers.Analysis on the mechanical properties of the coating show that the coatings microhardness increases prominently comparing with the substrate, which presents gradientdistribution with stable transition from the surface to substrate and is little influenced by thecoating composition for the good cladding quality specimen. The main strengtheningmechanisms of the coating are fine grain strengthening, hardy particles dispersingstrengthening, supersaturation solid solution strengthening and dislocation pile-upstrengthening. Microstructure of the coating is prominently refined compared with thesubstrate. The grain refinement behavior is related to the thermal and quality conduction, theincreasing of the inhomogeneous nucleation induced by the in-situ synthesized hardy particlesand the substructure refinement caused by the strong movement of the dislocation in thebonding metal matrix. The influence degree on the coating cracking behavior of the abovestress is related to the laser parameters, the coating compositions, the shape, size and thedistribution of the in-situ separating out phases. The materials abrasive resistance increasesprominently after laser cladding and the main abrasive mechanisms in the coating are abrasiveand desquamate caused by the above, which lie in the untreated substrate either, furthermore,adhesion appear in the substrate too.