The Study Of Technology And Properties Based On40Cr Surface Coating Preparation By Electron Beam

The medium carbon steel40Cr has good mechanical properties, and it’seconomical and practical, which has been widely used in machinery manufacturingindustry. However, the surface hardness is difficult to meet the higher requirementsoccasions, so it is necessary to improve the surface hardness and wear resistance of40Cr, but Traditional, single processing methods are difficult to meet the technicalrequirements. However，combining the electron beam modification and coatingtechnology provides a new way to solve this problem. Electron beam technology canpurify the material surface, increase the surface hardness of the material, and form alarge number of craters in the surface, increase the contact area the coating interface,thereby increasing the bonding force. After the electron beam coating process, thecoating surface can form remelting diffusion, and then form metallurgical bond. Thispaper aims to study materials technology composite and performance parts. Crcoatings are making preparation by magnetron sputtering， selecting differentparameters of electron beam irradiation treatment as auxiliary means. Besides, Twoprograms are designed to perform process and performance study. This topic by theNational Natural Science Foundation of China funded "UFG tooth surface gradientcoating technology and gear Properties"(ID:51275548), this thesis, compositematerials technology and performance parts. ProgramⅠ: Electron beam pretreatmentSurface Cr layer coating process studying; Program II: After the Cr layer surfacecoating, performing electron beam remelting process.Major work accomplished in this paper is as follows:(1) Research of Cr layer coating after electron beam pretreatment in40Cr surfacetechnology. It is performed to research on the influence law of electron beamparameters for the surface morphology and analyze the material hardness andimprovement of binding force under conditions of different parameters.(2)It is researching about the remelting process and performance of Cr layercoating on the surface of40Cr after electron beam. It is coated in the material surface,and the coating surface remelts in the use of electron beam irradiation. It revealed theelectron beam energy, electron beam irradiation times etc. process parameters on theinfluence of the coating quality, and got process parameters of coating qualityoptimization. (3) Study of coating friction and wear performance under the different process. Itis performed to research coating surface’s friction and wear performance underdifferent process conditions, and analyze the process influence law on the coefficientof friction, grinding crack width, wear, etc. Then these help to find optimizationcoating process of making the coating hardness distribution reasonably.The results confirm that the surface hardness of the irradiated specimen becamelarger as increasing the specimen size under the same voltage and irradiation times,when Cr layer was coated to surface of40Cr pretreated by electron beam.Meanwhile, the surface hardness presented an unevenly distribution, with greaterhardness in the surface edge than in the central portion. Compared with theun-pretreated case, the binding force of the coating improved in a range of33.3%～50%. This was relevant to that the bonding force increased with the increasing of theirradiation times. The average friction coefficient of coating surface pretreated byelectron beam is higher and changed more slowly than that of the coating surfacewithout electron beam pretreated, resulting in the prolonging of the early wear stagetime. Besides, the wear volume fluctuated with the increasing of the irradiation times,which proved the improvement of the friction and wear properties. Under theconditions of Cr layer being coated in40Cr surface after electron beam remeltingprocess, the surface area will produce white light. And Cr element content of thewhite light is3times of the area surrounding the region. While its hardness is lowerthan the surrounding region. And it will reduce the surface hardness of the materialperformance. Cr coatings by electron beam remelting can promote the production ofmetallurgical bond between the coating and the substrate and improve coatingadhesion. As the pulse voltage is increased, it will be enhanced for the diffusion ofthe elements Cr. However, the higher voltage and frequency will cause damage forcoating, because of reducing the Cr element content at the remelted layer. At thesame irradiation frequency, the higher the voltage is, the higher the substratetemperature is. And it is not benefit for the grain refinement more. While at the sameirradiation times, the more voltage’s increasing, the more surface cleanlinessimproves and the hardness increases. The friction coefficient of Cr coating samplesby electron beam remelting process in the initial stages is smaller than the untreatedsample. And the average coefficient of friction is lower; while at the same irradiationfrequency, wear properties by low voltage is better than by high voltage.