Preparation And Properties Of Fe-based Amorphous Composite Coatings

Electrical contact strengthening technology uses strong current to make the contact resistance intensely exothermic,the contact area is rapidly heated up,and under pressure,the coating material is welded to the matrix to form a metal protective layer.Compared with other surface technologies,the preparation of coatings by electrical contact strengthening technology has the advantages of high energy utilization,large heating rate,dense coating,simple operation,and large interfacial bond strength.For the first time,the authors of this paper have prepared high-performance Fe-based amorphous composite coatings using electrical contact strengthening technology,which provides a completely new solution for the preparation of amorphous coatings.First,Fe78Si9B13 amorphous alloy strip is directly wrapped to the surface of the 45 steel ring specimen,and then the thin strip is welded to the substrate by using electrical contact strengthening equipment.In this paper,the authors conducted a detailed study on the phase structure and microstructure of Fe-based amorphous coatings prepared by electrical contact enhancement technology,and explored and analyzed the effects of different process parameters on the microhardness,thermal shock resistance and wear resistance of the coating through orthogonal tests.The main research work and results of the thesis are as follows:During the service process of metal parts,the surface is prone to wear,which will result in part failure.Surface engineering is to prepare a small amount of coating materials with special properties on the surface of the substrate through various surface technologies,so that the substrate surface can obtain the performance it does not have and hopes to have,which can give full play to the application potential of coatings and matrix materials to achieve the effect of "1+1>2".Fe-based amorphous alloys exhibit excellent properties such as high hardness,wear resistance and corrosion resistance due to their special atomic arrangement.However,due to the extreme formation conditions of rapid quenching,the thickness of the material is greatly limited,and it mostly appears in the form of thin tape.At present,Fe-based amorphous alloy strip has achieved industrial large-scale production,low cost,excellent performance,as a coating material is easier to form a metallurgical interface with the carbon steel matrix.Therefore,as a metal thin film coating material,Fe-based amorphous alloy strip shows great potential in the application of surface engineering,which has important academic value and practical application significance.(1)A Fe-based amorphous composite coating with a thickness of 25?m to 75?m was prepared by electrical contact strengthening technology,and the surface quality of the coating was stable.Through EDS analysis,it can be seen that under the action of high temperature and pressure,element diffusion occurs between the coating and the matrix,forming a good metallurgical bond interface.The amorphous phase and the crystallized phase in the coating exist at the same time,the amorphous content can reach72.2%,and the crystallized phase precipitated mainly includes the ?-Fe(Si)phase and the Fe2 B phase,and the crystallization phenomenon of the coating is more obvious with the increase of the current.(2)The Fe-based amorphous composite coating prepared by electrical contact strengthening technology has a hardness of up to 976 HV,which is about 4.5 times the hardness of the quenched and tempered 45 steel matrix.From the orthogonal test results,the process parameters with the highest hardness are: current 20 k A,strip layer number 3layers,pressure 0.6MPa,strengthening cycle 4 times.Among all the factors,the magnitude of the current is the main influencing factor.When the current is 15 k A and20 k A,the ?-Fe phase grain in the coating is small,so it hinders the deformation caused by the movement of the shear belt,so the hardness shows an upward trend with the improvement of the current.When the current is 25 k A,the temperature exceeds the threshold of rapid grain growth and the deformation mode changes,and the microscopic deformation mode changes from shear belt motion to dislocation motion,so the hardness is reduced.Under the action of the heat affected zone and contact stress,the closer the workpiece matrix part is to the interface,the more obvious the grain refinement and the higher the hardness.(3)The study found that the Fe-based amorphous composite coating prepared by the electrical contact strengthening technology can play a good protective role on the matrix.The wear resistance of the coating is 3 times that of the 45 steel matrix.From the orthogonal test results,it can be seen that the best combination of process parameters for wear resistance indexes is: current 20 k A,strip layer number 2 layers,contact pressure 0.6MPa,strengthening cycle 4 times,of which current is the main influencing factor.The diffusion strengthening effect of the precipitated grains helps to improve the wear resistance of the coating.When the contact pressure increases,the bonding strength of the coating increases,and the wear resistance is also improved.The wear mechanism of the coating is stratification spalling and fatigue wear.(4)Fe-based amorphous composite coatings prepared by electrical contact strengthening technology have good thermal shock resistance.The highest number of thermal shocks measured when the coating peels off is 133 times.Through the analysis of the range,it can be seen that the primary and secondary factors affecting the thermal seismic performance index of the coating are: current,pressure,number of layers,and strengthening period,and the optimal process parameters are current 25 k A,pressure0.6MPa,layer number of layers is 1 layer,and 3 strengthening cycles.After analysis,high temperature and pressure are conducive to the diffusion of elements at the interface junction,so that the distribution of elements between the coating and the matrix is more continuous,dense and uniform,the bonding strength between the coating and the matrix is improved,the germination and expansion of cracks are effectively inhibited,and the thermal shock resistance of the coating is improved.