| There are two main problems in the traditional anodic oxidation process:one is that strong acids and alkalis and fluoride ions that were widely used in traditional anodizing electrolytes are notorious hazards to the environment and health of operators;the other is that titanium alloy treated by this traditional technology cannot meet the demand of growing industry for long-term or new application.So this article stands out of research body in two aspects.Firstly,malic acid was explored as green electrolyte for the first time to grow anodic film on Ti-10V-2Fe-3Al alloy.Secondly,the enhancement effect of adding particles and sealing method on anodic film were studied.In the paper,composite anodic film was fabricated on Ti-10V-2Fe-3Al alloy by one-step anodizing in malic acid with polytetrafluoroethylene（PTFE）nanoparticles in suspension.The influence of the key factors such as frequency,current density,anodizing time,malic acid and PTFE concentration was studied systematically.As a result,the parameters of composite anodic oxidation were optimized based on wear resistance.A comparison was made between the films produced by composite anodizing and sulfuric/phosphoric acid anodizing,respectively.The anodic film obtained in malic acid was sealed by layered double hydroxides（LDHs）.The morphology,phase,composition and properties of the composite and sealing anodic films were investigated.Finally,a plausible wear mechanism was proposed.The characteristics of the samples were analyzed by using SEM,AFM,XRD,Raman,EDS and GDOES.The composite anodic film had a surface full of holes and cracks,and PTFE nanoparticles tended to distributed in the structure of holes and cracks.The surface of sealing anodic film was covered by a fine and compact lamellar structure attributed to the morphology of LDHs layer.The composite and sealing anodic film thicknesses were 18 and 14μm.The thickness of the LDHs layer on anodic film was about 1.3μm.TiO2 in these films were mainly amorphous with little anatase.Moreover,corrosion and wear resistances of various samples were measured by electrochemical measurements and tribological tests,respectively.The corrosion current density and wear rate of the composite anodizing sample were respectively reduced by nearly 70%and 98%compared with the sulfuric/phosphoric acid anodizing sample.The corrosion current density and wear rate of the anodic sample obtained from malic acid were respectively reduced by about 97%and 47%after LDHs-sealing.The wear of the titanium alloy substrate was mainly abrasive wear.The sulfuric/phosphoric acid anodizing sample also displayed abrasive wear,because the protective film on the sample was destroyed.The wear track of malic acid anodizing sample revealed a delamination structure.This anodic film was not worn through during tribological tests and yielded a low wear rate,indicating high wear resistance.Both PTFE nanoparticles and LDHs nanosheets can played as lubricant and thus decreased friction coefficient significantly.Therefore,the samples after composite anodizing or sealing had better wear resistance. |
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