Research On Preparation Technology Of Laser Cladding Ion Sulphurization Compound Solid Self-lubricanting Layer

Marine power systems are critical components in seawater pumps.There are a lot of high-speed,heavy-load friction pairs in them.Failure is often caused by corrosion and wear which directly affect the function of the entire power system.In order to overcome these problems,low temperature ion sulphurization and laser cladding technology were combined to prepare a composite solid self-lubricating coating.In this thesis,the study of sulfide layer was carried out,we established a physical model of laser cladding low temperature ion sulphurization.Meanwhile ultrasonic rolling nanocrystallization technology was added to this treatment technology,the aim was to create a method in preparing a both thick and uniform solid self-lubricating coating.SD-Ni55 powder was used in the laser cladding on 45 steel,the prepared sample was placed into low temperature ion sulphurization furnace to preserve heat at different temperature.By means of etching XPS analysis,we constructed a physical model of compound sulphurization layer.The result showed that the formation of laser cladding low temperature ion sulphurization compound layer was divided into two main steps.One was ion dissociation and recombination,the other one was sulfide adsorption and deposition.During sulfide formation process,the gray-black sulfide preferentially nucleate at grain boundaries to form island structure,island microstructure connected to each other to merge a network organization.The organization grew along lateral direction,and accumulated along the longitudinal direction.With the heat preservation time prolonging,sulfide layer emerged dents,cracks,and partially peelings.Excessive activity S would react with Fe,FeS to form FeS2 which had harmful effect to self-lubricating properties.We use homemade ultrasound rolling nanocrystallization device for processing laser cladding layer,after ultrasound rolling treatment,the average grain size was minimized to 26.10 nm.XPS etching analysis showed that,compared to non-nanocrystallization laser cladding sulphurization layer,Fe content of nanocrystallization laser cladding sulphurazation layer was increased from 35.53% to 52.73%,but the remaining element content changed little.The rich Fe content in favor of the generation of FeS,and suppressed the generation of FeS2.FeS content in nanocrystallization laser cladding sulphurization layer was higher than non-nanocrystallization laser cladding sulphurization layer.XRD results indicated that phases of nanocrystallization laser cladding sulphurazation layer and non-nanocrystallization laser cladding sulphurization layer were consistent with each other,the differences existed in the relative amounts of the various phases.The composite sulfide layer of nanocrystallization specimen was dense and uniform,edge effect was small.Hardness of laser cladding layer which under nanocrystallization treatment was 58 HRC,it was higher than the original laser cladding layer by 5 HRC,hardness distribution of overlapping zone and weld was even,nanocrystallization treatment reduced surface irregularities and made surface roughness distribution uniform of laser cladding layer,after nanocrystallization,the thickness of laser cladding compound sulfide layer could be about 10?m.Its performance was good.Friction and wear evaluation showed that under the same dry friction conditions,friction coefficient of compound sulfide layer whose laser cladding layer was treated by nanocrystallization was 0.45.It was significantly less than the specimen which laser cladding layer was not treated by nanocrystallization.After 30 minute test,wear loss of compound sulfide layer of laser cladding layer was treated by nanocrystallization was 0.8 mg.And the wear loss of specimen of laser cladding layer without nanocrystallization was 1.2 mg.Nanocrystallization can also reduce wear scar width and depth of the compound sulfide layer.The most obvious effect of anti-friction was nanocrystallization specimen under oil lubrication conditions,the wear scar width of it was 0.447 mm and the depth was only 1.56 ?m.