Investigation On Corrosion And Wear Resistance Of Titanium Alloy Via Alkalized/Laser Texturing Technology

Titanium alloy is widely used in biomedical fields due to its good biocompatibility,excellent mechanical property,and good corrosion resistance.However,the natural formed oxide film on the surface is thin and tends to chip in the human body environment,which in turn leads to its poor corrosion resistance.Meanwhile,the poor wear resistance is also an important factor that shorten the lifetime of titanium implants.Hence,to improve the biological activity and abrasion resistance of the titanium alloy surface is one of the keys to prolong the service life of titanium alloy implants and promote its application in clinical.In this thesis,a combined technology of alkalizing and laser texturing including laser texturing(LT),alkalizing/laser texturing(ALT),and laser texturing/alkalizing(LTA)was applied to improve wear and corrosion resistance of Ti alloy.The phase constituents and surface morphology of the samples were investigated using X-ray diffraction and Laser Scanning Confocal Microscope(LSCM).The wear and corrosion resistance was evaluated based on the wear experiments and electrochemical corrosion experiments.In addition,positron annihilation experiments were carried out.The effect and mechanism of internal defects on the corrosion resistance of samples after laser texturing were revealed.The results are concluded as following.XRD analysis showed that the main phases of the samples process with ALT and LTA technology consist of sodium titanate,Ti,TiO2 and other titanium oxides.However,no characteristic peaks of NaTi2O4 were detected from the surface of ALT samples.Laser scanning space has a significant influence on the morphology and surface roughness,but no significant influence on the phase constituents.The results of LSCM revealed that a textured morphology with periodical pits and evenly cracks was realized on the surface of the samples after LT,ALT and LTA treatment.As scanning space decrease,rougher pits and more cracks were observed.Compared to LTA,ALT treatment presents less cracks and smoother morphology.The results of wear resistance showed that the samples after ALT and LTA processing present more excellent wear resistance than Ti alloy control.The samples after LTA treatment at laser scanning space of 1.6 mm present the minimum weight loss and coefficient of friction,indicating that samples after LTA treatment at laser scanning space of 1.6 mm present excellent wear resistance.Wear mechanism can be characterized as adhesive wear and abrasive wear.The results of electrochemical corrosion experiments showed that after alkalizing treatment the samples present improved corrosion resistance.The samples treated by ALT present better corrosion resistance at laser scanning space of 1.6mm.Overall,The samples processed by ALT at laser scanning space of 1.6 mm present improved and better corrosion resistance.The positron annihilation experiments and theoretical analysis indicated that the pulse width has a significant influence on the life time of positron,which in turn effect on the size and quantities of defects.After laser texture treatment at pulse width of 0.8 ms,1.0 ms,and 1.1 ms,the volume of vacancy cluster and vacancy-like defects in Ti alloy increased,the average size of defects also increased,while the whole number of defects decreased,this in turn can restrain the corrosion tendency and improve the corrosion resistance of Ti alloy control.Compared the corrosion resistance results at different pulse width,it can be concluded that the samples laser textured at laser pulse width of 1.0 ms present minimum size and lest quantities of defects,in turn present best corrosion resistance.