Study On The Theory And Experiment Of Anode Plasma Electrolytic Saturation Modification Of Steel Surface

Plasma electrolytic saturation is a new surface modification technology,which can be used to infiltrate C,N,B and other interstitial elements into the surface of steel to improve the micro-hardness and wear resistance of steel surface.It has been the focus of researchers,but most studies have focused on the cathode plasma electrolytic saturation,due to the saturation mechanism,choice of electrolyte systems,process of saturation layer formation,selection of process parameter and how to form a stable vapour–gas envelope are not enough in-depth,lead to the lack and disunity of result data about the anode plasma electrolytic saturation.Therefore,On the basis of further analysis of plasma electrolytic saturation theory,the surface of #45 steel was modified by anode plasma electrolytic saturation to prepare a modified layer with excellent hardness and wear resistance.Firstly,the flow field in the electrolytic cell is simulated to optimize the structure of the electrolytic cell and promote the formation of vapour–gas envelope and stable discharge.Then the mechanism of the anode plasma electrolytic saturation and possible electrochemical reaction in the electrolyte are analyzed,with the optimal selection of urea as the main electrolyte in the electrolytic system,completed the carbonitriding under different process parameters,with boric acid as the main electrolyte in the electrolytic system,completed the preparation of hard layer under different process parameters.Scanning electron microscope,energy spectrometer,X-ray diffractometer and microhardness tester etc.were used to test the morphology,structure,composition and microhardness etc.of the modified layer.Flow field analysis in electrolytic cell shows that the flow direction of the electrolyte has a significant effect on the uniformity of the flow field distribution in the electrolytic cell,and the pressure and velocity distribution in the electrolytic cell change with the change of the flow direction of the electrolyte.When the inlet and outlet are arranged parallel to each other on the same plane and are not on the same line,the flow field in the electrolytic cell is the most uniform in the initial stage of electrolysis,and the fluid fluctuation near the anode plate is the smallest,which is conducive to the formation of vapour–gas envelope and stable discharge.The influences of electrolytic voltage and treatment time on the composition,structure and microhardness of the modified layer were most obvious in the experiment of carbonitriding.With the increase of voltage and time,the thickness of the modified layer has an upward trend,up to 170 μm.When the voltage was 280 V and the treatment time was 5min,the nitrogen content of the near-surface modified layer was the highest,up to 1.23%,and the carbon content also reached 1.73%,which was significantly higher than that of the substrate.In terms of phase composition,nitride phase and carbide phase appeared in the samples after treatment.When the voltage and time changed,the form of nitride in the modified layer changed obviously.The changes of voltage and time also had a great impact on the microhardness of the modified layer.It was found that when the voltage and time were 280 V and 10 min respectively,the highest section hardness of the sample reached 889.5 HV,which was 4 times higher than that of the substrate.When the electrolytic voltage was 280 V and the treatment time was 5min,the lowest average friction coefficient was 0.20,and the wear weight was 0.3mg.The surface quality after treatment was the best.In the process of prepare hard layer by plasma electrolytic boriding,it was found that boride Fe B,Fe2 B occurred on the treated sample after phase analysis.In 10% boric acid + 5% ammonium chloride electrolyte,electrolysis at 300 V for 10 minutes,the highest section hardness 1235.4 HV was obtained,which was 5.6 times higher than that of the substrate.Generally speaking,the increase of hardness of boronizing is more obvious than that of carbonitriding,and the increase of hardness is bound to improve the wear resistance.The dry friction coefficient of the boronized layer was lower than that of the substrate under different electrolytic voltages,and the friction coefficient gradually decreased with the increase of the voltage,and the stable value was about 0.30~0.40,while the friction coefficient of the substrate was 1.02.When the electrolytic voltage was 300 V and the treatment time was 10 min,the surface quality was the best with the lowest average friction coefficient of 0.24 and the low wear weight of 1.3mg.