Study On Preparation And Properties Of Nano Submicron （Ti-V）C/Fe Ultrafine-Grained Laser Cladding Layers

In actual production,a large number of substrates to be cladding are steel mechanical parts.Considering the linear expansion coefficient and cost performance of cladding materials,iron-based alloy powders have good application prospects.However,in some working conditions,the pure iron-based cladding layer can no longer meet the application requirements.The ceramic particle-reinforced iron-based laser cladding layer has received extensive attention in recent years because it can obtain an ideal combination of properties.This subject is based on the research of iron-based laser cladding alloy powder.By adjusting the particle size of the gradient alloy powder and optimizing the laser cladding process parameters,the ultra-fine-grain high-performance cladding layer is prepared.The effect of the particle size of the reinforcing phase and the size of the matrix grains on the performance of the cladding layer is studied,and the relevant research on the corrosion resistance of the cladding layer is focused on.Three kinds of（Ti-V）C/Fe cladding layers with different microstructure sizes were prepared by setting the gradient particle size of the cladding alloy powder and the laser cladding process parameters.The phases of the cladding layer are all composed ofα-Fe and a small amount ofγ-Fe phase,and a certain amount of TiC and TiVC₂ are generated in the three kinds of cladding layers.Due to differences in the size and shape of carbides in the cladding layer and the size of the matrix grains,the corrosion resistance of the cladding layer is different.It is concluded through electrochemical tests and immersion tests that the refinement of carbides inhibits the galvanic corrosion of the cladding layer,thereby improving the corrosion resistance of the cladding layer.The laser cladding technology is used to prepare a wear-resistant cladding layer with low dilution rate,small stress and deformation,and metallurgical bonding with the matrix to improve the life of the parts that are easy to wear.The iron-based composite laser cladding layer with micron and sub-micron（Ti-V）C as the reinforcing phase was prepared.The sameα-Fe,γ,TiC and TiVC₂ phases were found in the two cladding layers.The average grain size of Fe matrix is 3.46μm and 3.37μm,the microhardness is 731HV_0.2and 736HV_0.2,and the area ratio of carbide is 11.14% and 11.02%,respectively.The wear resistance of a cladding layer with a carbide-reinforced phase grain size of 1.95μm under dry sliding conditions is 2.76 times that of a cladding layer with a carbide-reinforced phase grain size of 0.49μm.The failure mechanism of the micron carbide cladding layer in the friction and wear test is caused by the plastic deformation of the cladding layer matrix,while the failure mechanism of the sub-micron carbide cladding layer involves not only the plastic deformation of the cladding layer matrix,but also Abrasive wear caused by exfoliated carbides.An ultra-fine-grained iron-based laser cladding layer with 42Cr Mo steel as the matrix and nano-and sub-micron TiC as the reinforcing phase was successfully prepared.The cladding layer is well formed without defects such as pores and cracks.The structure of the cladding layer is mainly composed of lath martensite,retained austenite and TiC.The particle size of TiC is between 0.04 and 1.10μm,and the average particle size is 0.25μm.In addition,98.9% of TiC reaches the sub-micron level,and 11.0%reaches the nano-level.The average grain size of the iron-based alloy is 4.08μm,reaching the ultra-fine grain level.Compared with the 42Cr Mo matrix,the hardness of the cladding layer is increased by 425HV_0.2,and the corrosion resistance is increased by 2.39 times.VC,which has similar physical properties to TiC,is also often used as a reinforcing phase to be added to composite materials.Nano-VC reinforced sub-micron ultra-fine-grained iron-based laser cladding layer was prepared by using gradient particle size alloy powder.The microstructure of the cladding layer is granular V₆C₅ and lath martensite.Approximately 95% of the carbides reach the nanometer level,and the average particle size of the carbides is 53 nm.About 71.60% of the cladding layer matrix crystal grains reach sub-micron level,and the average crystal grain size of the cladding layer matrix is0.90μm.The performance of the cladding layer was tested and found that the hardness of the cladding layer was 600HV_0.2 higher than that of low carbon steel,and the corrosion resistance was increased by 21.60 times.In the initial stage of the immersion experiment in 3.5wt% Na Cl solution,the corrosion products of the cladding layer consisted of Fe₂O₃and Fe₃O₄.After immersion for 8 hours,a dense oxide film with only Fe₂O₃ was formed.In the early stage of the high-temperature oxidation test,the high-temperature oxidation of the cladding layer increased more than the weight gain of low-carbon steel.After 7hours of high temperature oxidation,a dense oxidation product film gradually formed on the surface of the cladding layer,which made the oxidation growth rate of the cladding layer slowly increase.