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Surface Modification on 45~# Steel with Plasma Electrolytic Saturation in Solution

Author: ZhangRong
Tutor: HaoYuan；MaYing
School: Lanzhou University of Technology
Course: Materials Science
Keywords: solution plasma electrolysis saturation carburizing carbonitriding
CLC: TG174.4
Type: Master's thesis
Year: 2009
Downloads: 132
Quote: 1
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Abstract


Plasma electrolytic saturation in solution is a new technology in materials’ surface treatment.Wear resistence and corrosion resistence are improved by adopting PES technology saturating carbon、nitrogen、carbonitriding rapidly into ferrous metals materials.Plasma electrolytic saturation in solution was applied for surface modified Of 45# steel.The experiment optimize research is an important part.In this part,the formulate of NaCl-C3H8O3 system has benn optimized.The pulses,occupy-empty ratio,current frequency influence formation of surface modification layer on the 45# steel by PES are also studied.The condition of forming excellent surface modification layer is found through lots of experiments.On the basis of electrolyte formulation,process parameters determined principles.Research treatment time to the effects of surface modification layer in NaCl-C3H8O3 system and NaCl-HCONH2 system.The surface modification layer changes were analyzed and compared at the same time to different types of electrolyte and different time to the same electrolyte.Morphology,structure of surface modification layer is observed by SEM.The phase constitue of surface modification layer is measured by XRD and so on.The study showed that resistance（to be dealt with samples） voltage-current characteristics follow Ohm’s law at the initial stage of the experiment in NaCl-C3H8O3 system and NaCl-HCONH2 system.If the voltage between electrodes continues to increase then the current also increases rapidly at this time,no longer accord the Ohm’s law.The influence of electrical parameters on surface modification layer,such as the occupy-empty ratio pulses,pulse width determines the duration of spark discharge and the density,the increased pulse width and will be beneficial to the hardness of the surface modified layer,but after high discharge pulse width will become more intense, thus increasing the surface roughness of the samples.Electrolyte layer formed on the surface modification has far-reaching implications,different electrolyte the growth rate of surface modification layer structure,composition and elements distribution are different.The temperature influence on the process of plasma electrolytic saturation, the temperature is too high,the voltage of work can not be too high,if the voltage is too high,easy flying electrolyte,local ablation or breakdown are easy occur surface modification layer.The surface modification layer of 45# steel is made up of PES coating,difficusion layer and transition layer.Applied AC pulse power in NaCl-C3H8O3 system and NaCl-HC0NH2 system can achieve carburisng and carbonitriding layer in 45# steel. The thickness of surface modification gradual increase as the processing time to extend in the same electrolyte,with the treatment time extension,the rate of infiltration is reduce,which is due to the concentration of plasma region relatively high at the initial stage,the activity of atoms beginning of infiltration when surface area of work and the plasma aera form concentration gradient,the activity of atoms infiltration to the surface workpiece,concentration gradient are created in surface and internal,so the activity of atoms from the surface to continue to the internal difficusion,the processing time up to a certain value,the workpiece surface and the internal concentration gradient are reduce and activity atomic infiltration speed are slowed,so when thickness reaches a certain value,the growth rate slowing down with the infiltration rate reduce.Different electrolyte system dealing with the same time penetration is relatively high efficiency and the quality of the surface modified layer is relatively good in NaCl-HCONH2 system.Surface holes increased with the processing time extend in the same electrolyte system,the holes were partially membrane breakdown,the plasma discharge formation channel.The same electrolyte system deal with different time the composition surface of modification layer and phases are basically same.Different electrolyte system dealing with the same time the composition surface of modification layer and phases are different.This surface modification layer mainly composed of Fe,C,N,the main phases are Fe-C,Fe-N compounds,because of Fe-C,Fe-N phase is enhanced,which can improve the surface of 45# steel performance. Be processed through the sample Vickers,Brinell,Microhardness analysis is understood that the hardness of the sample being processed are greatly enhanced.In NaCl-HC0NH2 system of carbonitriding the thickness of modified layer and hardness better.Through EPMA and EDS analysis further identified the possibility of carburizing,carbonitriding and infiltration of elements distribution a more even.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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