Study On Fe-based Amorphous Microstructure

With the rapid development of the contemporary industrial field,due to the use needs in many fields,materials with high hardness,corrosion resistance and high temperature resistance are often required,such as blades,rotors,bearings of aerospace engines.However,due to such materials,single material components meeting the requirements under harsh conditions will lead to increased costs.Materials that have been subjected to corrosion,oxidation,and abrasion are obsolete due to service life limitations.Therefore,the protection and maintenance of components have become particularly important.As a strong protective effect coating,iron-based amorphous coatings have been considered for coating protection and have been widely studied.In this paper,a laser cladding technique is used to perform an iron-based amorphous alloy coating test on the surface of Q235 plate.The effects of laser processing on the microstructure,microhardness,room-temperature friction and wear,and nano-indentation properties of the amorphous coating are studied.The phase composition of the laser cladding coating at different scanning speeds was observed by XRD.The morphology and element distribution of the coating structure were further determined using TESCAN scanning electron microscopy and Oxford spectroscopy.Combining XRD and scanning electron microscopy results,the main phase composition of the coating is:M23C6（M=Fe,Cr,Mo）,γ-（Fe,Cr,Mo）,and bcc-fe three scanning speeds with laser cladding The enhancement of Zn decreases the content of crystalline phase and increases the peak width.When the scanning speed is 3000mm/min,the coating can be divided into three layers from the bottom to the top according to the different morphology of the coating:the first layer is columnar crystals,the second layer is a unit structure filled with a crystalline phase,and the third layer is The unit structure consists of a crystalline phase and an amorphous phase.The unit structure of the third layer in the coating was analyzed by TEM.It was found that the amorphous phase and M₂₃C₆ coexisted in the amorphous gray area,and the crystalline phase of the white crystalline phase with different shapes wasγ-（Fe,Cr,Mo）.When the laser scanning speed is slow,the bcc-fe phase is distributed in the coating in the form of equiaxed crystals.The microhardness test results show that the microhardness value of the coating is 1447.9HV and the average microhardness is 1353HV when the scanning speed is 3000mm/min.The friction and wear test results show that the coating has better anti-friction and wear resistance than the base material,and the depth of the wear scar is nearly 20 times smaller than that of the base.The results of the nanoindentation experiments indicate the differences in the hardness of different micromorphologies and phases in the coating,and it is these differences that provide the coating with a certain degree of plasticity,so that the coating does not generate cracks during the nanoindentation experiment.In order to reduce the large residual stress caused by the uneven distribution of solute in the coating,which causes micro-cracks to appear in the coating,the method of adding a longitudinal alternating magnetic field during the laser cladding process makes the melt during the laser cladding process affected by the magnetic field.Produces a stronger agitation effect and reduces defects caused by rapid solidification of the coating.The experimental results show that the addition of the magnetic field reduces the volume of the white particle phase in the coating,and the area of the irregularly shaped gray area increases significantly.The addition of a magnetic field effectively reduces the tendency of the coating to crack.TEM analysis of the area after the nano-indentation test of the coating found that the coating showed plastic toughness and no cracks appeared in the area near the nano-indentation even under the condition of external force loading.