Improving Tribological Performance Of 316 Stainless Steel By Surface Texturing-plasma Titanizing Duplex Treatment

Austenitic stainless steel?ASS?is distinguished with its promising integrated mechanical properties and desirable formability,excellent corrosion resistance in oxidizing and reducing media.Therefore the ASS has long been considered as one kind of indispensable structural material in many sectors ranging from industrial and civilian goods to military equipment.At present,ASS posses multiple types,it is also characterized as the most widely utilized type of stainless steels in widespread usage area.With the development of production and processing technology,ASS is meeting more wider application conditions.However,the ASS is seldom operated in tribological-related engineering conditions by the drawbacks of low surface hardness values,high coefficient of friction and poor wear resistance.The wearing damage usually generates on the material surface while surface engineering technologies allow the realization of a new structure,component and performance.Surface treatments have been extensively applied to improve the tribological performance of ASS.Surface texturing?ST?and double glow plasma surface alloying?DGPSA?have their own advantages in enhancing the tribological performance of materials.By combining the mentioned two methods,the duplex treatment is expected to furtherly improve the tribological performance of ASS.In this work,the duplex treatment was realized by ST-DGPSA:firstly,electro spark machining?ESM?was conducted on 316 stainless steel?316 SS?surfaces to obtain groove-shaped texture.Then the textured 316 SS samples were subjected to titanizing through DGPSA.The material characterizations of the duplex treated 316 SS were analyzed.The tribological behaviors of 316 SS substrates,surface textured 316 SS,titanizing coatings and duplex treated 316SS were investigated under dry friction and grease lubrication.Meanwhile the corrosion resistance of the related samples in 3.5%sodium chloride solution was estimated.The main contributions are as follows:?1?Orthogonal design method was adopted to set the experiments for producing the titanizing coatings,and the effects of process parameters including:testing temperature,soaking time,voltage difference between the source electrode-piece electrode and the distance between the source electrode-piece electrode on the thickness values and wear resistance on the titanizing coatings were systematically studied.While the optimal titanizing process parameters for 316 SS were:DGPSA at 950?for 3 h with a 200 V voltage difference and a distance of 18 mm between the source electrode-piece electrode.Under this parameter,a continuous and compact titanizing coating with a thickness of about 10?m was received.The titanium showed a gradient distribution from surface toward substrate in the titanizing coating.A metallurgical bonding was obtained between the titanizing coating and the316 SS substrate.Ni Ti₂,NiTi,Ni₃Ti,Fe₂Ti and Cr₂Ti were detected in the titanizing coating via X-ray diffraction?XRD?.The titanizing coating revealed a surface hardness of 636.6 HV_0.1.1 and a bonding strength over HF1 level.?2?Under dry friction,the titanizing coatings indicated higher friction coefficients than those of 316 SS substrates as they were sliding against GCr15and Si₃N₄.The titanizing coating showed no friction-reduction effect but better wear resistance in comparison to 316 SS substrates.When the friction tests were performed under grease lubrication,the titanizing coating also revealed slightly high friction coefficients as compared with 316 SS substrates.However,the specific wear rate of titanizing coating was an order of magnitude lower than those of 316 SS substrates as countering with GCr15 and Si₃N₄.?3?The surface textured 316 SS and duplex treated 316 SS presented similar variation tendency of friction coefficients,and the duplex treated 316 SS samples exhibited lower friction coefficients than those of surface textured 316SS samples under dry friction against GCr15 and Si₃N₄.On the other hand,the surface textured 316 SS samples suffered more severe damage in comparison to the duplex treated 316 SS samples.The groove-shaped texture had well played the effect of capturing wear debris and significantly reduced the wearing degradation of surface textured 316 SS and duplex treated 316 SS.Under grease lubrication,the groove-shaped texture acted as grease storage and provided continuous lubrication.The surface textured 316 SS and duplex treated 316 SS had received slight wear damage indicating by their discontinuous wear traces.The duplex treated 316 SS underwent more mild wearing than the surface textured 316 SS.?4?The electrochemical measurements of open circuit potential?OCP?,polarization curve and electrochemical impedance spectroscopy?EIS?were used to estimate the corrosion resistance of the relevant 316 SS samples.It was seen that the titanizing coating and the duplex treated 316 SS had superior corrosion resistance to the 316 SS substrate reflecting by higher OCP and charge transfer resistance values,lower corrosion current densities.The surface textured 316 SS which possessed certain hydrophobic property,also demonstrated better corrosion resistance than that of 316 SS substrate according to the results of electrochemical measurements.?5?Taken as a whole,both DGPSA with titanizing and duplex treatment of ST-DGPSA with titanizing had remarkably enhanced the tribological performance and corrosion resistance of 316 SS substrate.It was worth emphasizing that the duplex treated 316 SS displayed more significant improvement.