Research On The Synergistic Effect Of Oxidation And Complexation On Tribochemistry Removal Mechanism And Process Of Titanium Alloy

Titanium and titanium alloys are widely used in biomedicine,aerospace,shipbuilding,and other fields because of their high strength-to-weight ratios,excellent fatigue resistance,extraordinary corrosion resistance and biocompatibility.Based on the national development strategy,it is currently in a critical period for the development of materials with excellent properties represented by titanium alloys.However,titanium alloy is a typical difficult-to-cut material with high machining difficulty and low machining efficiency.At present,the manufacturing process of titanium alloy parts is still the traditional milling,grinding,turning and ultra-precision turning.It is difficult to achieve the excellent surface quality and surface integrity of titanium alloy materials.The defects produced by processing will significantly reduce the reliability and fatigue life of titanium alloy parts,thus,it is difficult to achieve extensive application in high-end equipment and high-end parts.Chemical mechanical polishing based on tribochemical removal mechanism is one of the most effective means to solve the problems of surface and sub-surface defects and damage of titanium alloys.Therefore,in view of the practical problems existing in the current chemical mechanical polishing of titanium alloys,such as the lack of micro removal mechanism and the difficulty of efficient and high-quality removal,it is urgent to reveal the material removal mechanism of chemical mechanical polishing of titanium alloys,put forward new processing technology,and realize the efficient and high-quality removal of titanium alloys on the basis of further enriching and expanding the tribochemical removal theory,to promote the further application of titanium alloys in biomedical and aerospace fields.Based on the mechanism of tribochemical removal,chemical mechanical polishing is adopted to study the process of high-efficiency and high-quality surface manufacturing of titanium and titanium alloys.Firstly,the action mechanism of different pH and typical oxidizer H₂O₂on the tribochemical removal of titanium and titanium alloys is studied,and the influence law and action mechanism of various factors on the removal performance in the tribochemical removal process are clarified.It is found that the oxide film is the key factor affecting the efficient removal of titanium alloy surface,The feasible way to achieve efficient removal is to destroy the rapidly formed oxide film through efficient complexation;Then,considering the polishing efficiency and the actual polishing environment,the effective chemical additives were screened for rapid oxidation and high-efficiency complexation under acidic conditions,the synergistic effect of F^-and persulfate was chosen,and the influence law and mechanism of their synergistic effect on the tribochemical removal performance of titanium alloys were revealed;Meanwhile,in order to maintain the good biocompatibility of the surface oxide film and avoid some negative effects of F^-on biological cells,the synergistic effect of H₂O₂ and K⁺under alkaline conditions was chosen,and the influence law and mechanism of its synergistic effect on the tribochemical removal performance of titanium alloys were revealed;Finally,using the above tribochemical removal mechanism,the process of efficient and high-quality surface manufacturing of the curved titanium alloy by flexible chemical mechanical polishing provides a method and basis for application-oriented titanium alloy curved surface polishing.The main research contents of this thesis are as follows:(1)The influence law and mechanism of pH and H₂O₂ on the tribochemical removal of titanium alloys were revealed.It is found that the oxide film is the key factor affecting the efficient removal of titanium alloy surface.The feasible way to achieve efficient removal is to destroy the rapidly formed oxide film through efficient complexation.Acidic conditions can promote the corrosion of titanium alloy oxide layer and enhance mechanical removal,and the addition of different concentrations of H₂O₂ will change the compactness of oxide layer.When the concentration of H₂O₂ is 0.05 wt%,the material removal rate of titanium alloy reaches the peak.When the excessive oxidation of titanium alloy exceeds the mechanical removal capacity of Si O₂ particles,it will inhibit the material removal of titanium alloy.(2)Considering the polishing efficiency and the actual polishing environment,effective chemical additives were screened for rapid oxidation and efficient complexation,and the synergistic effect of F^-and persulfate under acidic conditions was chosen.On the premise of ensuring the surface quality with roughness below 3.5 nm,the material removal rate was 1.4times higher than the maximum material removal rate reported in the literature.At the same time,the effect of the synergistic effect of F^-and persulfate on the efficient tribochemical removal of titanium alloys was revealed,and chemical reaction equations and the mechanism of the synergistic effect were clarified.When the polishing solution contains 80 m M Na F and100 m M(NH₄)₂S₂O₈,the material removal rate of titanium alloy reaches 203 nm/min,the surface roughness Ra reaches 3.4 nm,and there is no damage underneath the oxide film.HF,F^-and HF₂^-produced by the ionization of F^-in acid continuously and efficiently corrode and complex passivate the oxide film,while persulfate continuously and rapidly generates new oxide film.When the chemical action of F^-and persulfate and the mechanical action provided by abrasive particles reach a dynamic balance,titanium alloys can achieve efficient and high-quality material removal.(3)In order to maintain the better biocompatibility of the surface oxide film and avoid some negative effects of F^-on biological cells,the synergistic effect of H₂O₂ and K⁺under alkaline conditions was chosen.On the premise of ensuring the surface quality with roughness below 5 nm,the material removal rate is about 2 times higher than the highest material removal rate reported in the literature.At the same time,the influence law and mechanism of the synergistic effect of H₂O₂ and K⁺on the efficient tribochemical removal of titanium alloys were revealed.Under the conditions of 5 wt%H₂O₂ and pH 10,with the increase of K⁺concentration,the material removal rate of TC4 titanium alloy first increased and then stabilized,reaching the peak to 270 nm/min at 250 m M K⁺,with smooth surface and no scratch and no damage to the substrate.OOH^-generated by the decomposition of H₂O₂ under alkaline conditions can quickly oxidize titanium alloy.At the same time,the increase of K⁺concentration leads to the decrease of diffusion layer thickness and the enhancement of electric double layer repulsion shielding,making OOH^-and Si O₂ particles easier to approach the surface of titanium alloy.It continuously promotes OOH^-efficient corrosion and complexation of titanium alloy oxide film,enhances the mechanical removal of Si O₂ particles,and then realizes the efficient and high-quality removal of titanium alloy.(4)Based on the tribochemical removal mechanism in Chapter 4 and 5,the flexible tribochemical removal process of the curved titanium alloy was studied.The curved titanium alloy implant of humeral head in reverse shoulder replacement prosthesis was selected as a typical workpiece for flexible chemical mechanical polishing,and the corresponding clamping tool was designed.The rapid machining of the curved titanium alloy with material removal rate of 44 nm/min and surface roughness Ra of 2.7 nm was realized by synergistic effect of F^-and persulfate,then,the curved titanium alloy was polished with alkaline flexible chemical mechanical polishing slurry containing H₂O₂ and K⁺to remove the residual F^-,and finally the high-efficiency and high-quality surface manufacturing of the curved titanium alloy with surface roughness Ra of 2.3 nm was realized by two-step method.