Effect Of Carbide Compound Introduction Method On Microstructure And Properties Of Fe-based Laser Cladding Coatings

Laser cladding technology can fabricate high performance carbide reinforced metal matrix composite coatings on low cost substrates,which is of great significance to reduce production costs and improve the service life of parts.It has broad application prospects in the field of surface strengthening and repairing of parts.For carbide reinforced metal-based laser cladding layer,the introduction method of carbide has an important effect on the microstructure and properties of the cladding layer.NbC-reinforced Fe-based laser cladding layers were prepared by laser cladding technology using"ex-situ method","in-situ synthesis method"and"compound introduction method".Through systematic comparative study,the influence of"compound introduction method"of carbide on the microstructure and properties of cladding layer was analyzed.On this basis,a TiC-Nb-C system powder was designed to improve the forming quality and microstructure uniformity of the cladding layer.The results show that for NbC-reinforced Fe-based laser cladding layer,the carbides in the cladding layer obtained by the"ex-situ method"mainly exist in the?matrix as primary NbC with blocky and petal shape,and the proportion of net eutectic NbC is relatively low.The carbides obtained by"in-situ synthesis method"mainly exist in eutectic form,and NbC mostly has a fine lamellar structure.The microstructures of"compound introduction method"are between"ex-situ method"and"in-situ synthesis method".Numerous eutectic NbC and massive and petal NbC were distributed on the?matrix at the same time.Increasing the content of NbC and decreasing the content of Nb and C can inhibit the formation of eutectic structure and promote the formation of massive and petal NbC.On the contrary,more eutectic NbC can be formed.The content and formation rate of NbC in the cladding layer obtained by"ex-situ method"is the highest,while that of NbC in the"in-situ synthesis method"is the lowest,and that of"compound introduction method"is between them.Appropriately increasing the content of NbC in the cladding powder and reducing the content of Nb and C can increase the content and the formation rate of NbC.In addition,the presence of Fe₂Nb phase was also found in the cladding layer prepared by"in-situ synthesis method"and"compound introduction method".The hardness and wear resistance of the cladding layer obtained by"ex-situ method"are the lowest,and the wear mechanism is abrasive wear and slight adhesion wear.Moreover,a large number of holes appear in the cladding layer.The"in-situ synthesis method"has the highest hardness,the best wear resistance,and the wear mechanism is slight abrasive wear.However,the appearance of excessive eutectic structure increases the cracking tendency of the cladding layer.The"compound introduction method"is between them.With the increase of NbC content in the cladding powder,the wear mechanism gradually changes from slight abrasive wear to severe abrasive wear and adhesion wear.At the same time,there are cracks in the cladding layer.For the TiC-Nb-C cladding layer,the main phases are TiC,?Nb,Ti?C,Fe₂Nb and Cr-Ni-Fe-C.TiC cannot dissolve completely in the cladding process due to its high thermal stability.The undissolved TiC can be used as heterogeneous nucleation point for NbC to precipitate and grow on its surface,thus forming?Nb,Ti?C with coating structure.The introduction of TiC increases the nucleation point of carbides,which promotes the formation of primary carbides and greatly inhibits the formation of eutectic NbC.At the same time,the carbides are refined effectively.Therefore,the carbides in the cladding layer mainly exist in the form of small size block and discontinuous network.The overall distribution of the microstructure is more uniform.The introduction of TiC also increases the total content of carbides in the cladding layer,but due to the decrease of fine eutectic structure,the hardness and wear resistance of the cladding layer are slightly lower than those of NbC-Nb-C system.And the wear mechanism is abrasive wear and adhesive wear.In addition,the forming quality of the cladding layer has been significantly improved,and the forming defects such as porosity and cracks have been effectively suppressed.