| The fabrication of in-situ synthesized metal ceramic composite coating on common materials surface by laser cladding could achieve the good combination of the excellent properties of the metal matrix and the ceramic. The application prospect of this research field is wide at present. According to the above, the following aspects are discussed in this paper:According to the basis of △ GT, production of TiB2 is easiest in Ni-Fe-Ti-B and Fe-Ti-B coating reaction systems, and Ni4B3, TiB could be fabricated too. The protective atmosphere is very important during laser cladding process. Differential-thermal analysis of different coating reaction systems shows that the main reaction type is stable at different heating rate, but the thermal effect and the main reaction degree have a certain difference, and the start temperature of the reaction and the highest reaction speed temperature varies too. The amount of the units in polynary has effect on the two temperature points too. The kinetics equation based on Freeman-Carroll formula could describe laser cladding process approximately.Laser cladding in-situ reaction is a process deviating from equilibrium state in opening system, negative entropy could be induced in certain conditions, non-linear mechanism and fluctuation lie in the systems, which coincide with the formation conditions of dissipative structure in non-equilibrium systems advanced by Z.Prigogine, and experiment proves that self-organization arises and ordered and regular dissipative macrostructure formed.In-situ separating out Ni-Fe-Ti-B and Fe-Ti-B composite coating with different coating compositions are fabricated on the common 45 steel surface by laser cladding with optimal laser parameters, and the cladding quality is good in specimen SN1 and SN2 with optimal coating compositions and SF1, SF2, SF3 after composition regulating. Microanalysis on the coating is carried out available to material modern analysis methods. Results show that coating melting zone morphology and the crystal size evolving in a certain rule with the change of coating composition. Ni-Fe-Ti-B composite coating are mainly composed of γ- (Ni, Fe) and Nihcp metal matrix and a great deal of in-situ synthesized stable phases of TiB2, Ni4B3 and metastable phases of Ni2B, (Fe, Ni)3B type compounds. Fe-Ti-B composite coating are mainly composed of α -Fe metal matrix and in-situ synthesized stable phases of TiB2, Fe2B and metastable phases of TiB, Fe3B. They exist in the coatings melting zone with the state of the advanced eutectic metal matrix in the dendrites and eutectic mixture in intergranular. High density dislocation pile-up lies in the interface of the matrix and the second phase, which induce the sub-structure fining of the metal matrix. The output of the in-situ product varies with the content of the coating composition.Analysis on the mechanical properties of the coating show that the coatings microhardness increases prominently comparing with the substrate, which presents gradient distribution with stable transition from the surface to substrate and is little influenced by the coating composition for the good cladding quality specimen. The main strengthening mechanisms of the coating are fine grain strengthening, hardy particles dispersingstrengthening, supersaturation solid solution strengthening and dislocation pile-up strengthening. Microstructure of the coating is prominently refined compared with the substrate. The grain refinement behavior is related to the thermal and quality conduction, the increasing of the inhomogeneous nucleation induced by the in-situ synthesized hardy particles and the substructure refinement caused by the strong movement of the dislocation in the bonding metal matrix. The coating with high content of ceramic phases tents to cracking, which is mainly the following: the transcrystalline cracking in the matrix, the high density cracking in the edge of the coating, micro-cracking on the interface of the matrix and the hardy ceramic phases and in the vicinity of the bonding interface in th...
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