Studies On The Electrochemical Corrosion Behaviors Of Ti6Al4V Alloys Prepared By Different Processes

Titanium alloys are developed rapidly for aerospace,marine and biomedical applications owing to their attractive properties such as high strength to weight ratio and excellent corrosion resistance.As for Ti6Al4 V titanium alloy,a typical α+βtitanium alloy,its application amount exceeds 60% of the applications among all titanium alloys.Although titanium alloys exhibit a good corrosion resistance due to the stable oxide film formed on the surface,the corrosion of titanium alloys is accelerated by the cracking of the oxide film under the influence of their service environment,especially in wet,rainy,and coastal areas.For titanium alloys,the processing technologies commonly used are traditional casting,forging,rolling and 3D printing,etc.The microstructures of material prepared by different processes are obviously different.In addition,for 3D printed titanium alloys,there inevitably exist pore defects in the molding process.The microstructures and defects of the material usually affect the corrosion resistance,thus affecting the service life of material and structures.In this paper,the electrochemical corrosion behaviors of Ti6Al4 V titanium alloys prepared by different processes will be studied.It is of great significance to investigate the influence of processing technologies and microstructure on the corrosion behaviors of Ti6Al4 V alloys for engineering applications.In this work,the corrosion behaviors of Ti6Al4 V titanium alloys were studied by electrochemical corrosion experiment and numerical simulation.The main research contents are as follows:(1)The microstructures of traditional forging and 3D printed Ti6Al4 V alloys before corrosion were characterized by scanning electron microscope,and the porosity of 3D printed Ti6Al4 V alloys was determined to be 2.66%.At the same time,NaCl and HCl electrochemical corrosion solutions were prepared,and the physiochemical properties of seawater sample from Xiamen port were measured.(2)The polarization curves of Ti6Al4 V alloys prepared by 3D printing and traditional forging were measured in seawater,3.5 wt.%NaCl,3.5 wt.%HCl,5 wt.%HCl and 10 wt.%HCl.The corrosion kinetic parameters were obtained by extrapolation of Tafel,and the influences of processing technology and microstructure on the polarization curves of Ti6Al4 V alloys were analyzed.It was found that 3D printed Ti6Al4 V alloys show a worse corrosion resistance due to the pore defects which are effortless to enrich Cl’.Especially when the concentration of HCl is higher,the corrosion rate of 3D printed Ti6Al4 V alloys multiples or even increases by an order.This suggests that for the 3D printed Ti6Al4 V alloys,the deterioration of mechanical properties induced by corrosion damage should be assessed and considered during servicing.And the ratio of laser power to its scanning speed and phase constituent composition of the alloy also have a certain influence on the corrosion resistance of Ti6Al4 V alloys.(3)The electrochemical impedance spectra of 3D printed and traditional forging Ti6Al4 V alloys in seawater,3.5 wt.%NaCl,3.5 wt.%HCl,5 wt.%HCl and 10 wt.%HCl were measured.By fitting the equivalent circuit,the differences of electrochemical impedance spectroscopy between 3D printed and traditional forging Ti6Al4 V alloys were compared and analyzed,as well as the influence of microstructure on traditional forging Ti6Al4 V alloys and process parameters on the 3D printed Ti6Al4 V alloys were analyzed.Also the thickness of passive film was estimated.The results show that 3D printed Ti6Al4 V alloys have a worse corrosion resistance compared with the traditional forging Ti6Al4 V alloys,Meanwhile,microstructure is also an important factor affecting the corrosion resistance of Ti6Al4 V alloys.The results are similar to those obtained by the polarization curve analysis.(4)Based on COMSOL Multi-Physics,an electrochemical model was established for the titanium alloy/electrolyte interface.Numerical simulations of impedance were performed and thickness of passive film was estimated.Further,the galvanic corrosion mechanism of a and β phases in HCl solution was analyzed for Ti6Al4 V alloys,and the corrosion rate of β phase was predicted.The simulation results are in good agreement with the experimental results.Hence,numerical simulation method can be used to rapidly provide data support for corrosion assessment of Ti6Al4 V alloys in corrosion enviroments.