Mechanical Properties And Oxidation-Resistance Of The TC4 Alloy Treated By Plasma Immersion Ion Implantation

Ti6Al4V alloy has been used widely in many fields owing to its excellent mechanical properties, i.e. low density, high strength-to-weight ratio. However, more extensive utilization has primarily been hindered by its low hardness, inferior tribological properties and high chemical activity. When the alloy is brought into contact with oxidizer, for example, hydrogen peroxide, it will be oxidized quickly and dissolved into oxidation solutions. The two-phase structures played vital role for they have different chemical potential which can accelerate the electrochemical corrosion. Finally, the specimens were caused failure early. Thus, many techniques are highlighted in order to improve the oxidation resistance of the Ti6Al4V.The plasma immersion ion implantation (PIII) technique was employed to make a modification layer form on the surface of Ti6Al4V alloy in this paper, and the layer was expected to improve the resistance of oxidized properties. The five parameters were investigated systemically by using orthogonal experiments, including pulse bias voltage, radio frequency (RF) power, gas pressure, implantation time, class of implantation elements. Effect of those parameters on the mechanical properties and electrochemical corrosion and oxidized resistance was characterized by different techniques. Furthermore, the effect of the gas pressure on the mechanical properties, electrochemical corrosion behavior, and oxidation resistance was studied in detail at the condition of nitrogen-PIII. And the effect of implantation time on the properties aforementioned was also researched in detail at the condition of oxygen-PIII.The micro-hardness of modification layer was measured by dynamic ultra-microhardness tester with Vickers'diamond square-faced pyramid indenter, and the result showed that all the implantation samples are more hardness than the substrate. The friction coefficient was memorized in situ by the ball-on-disk friction machine made in our laboratory, and the integrated friction coefficient calculated was used as a standard to characterize the wear resistance. Moreover, the polarized curves of the implantation samples were also documented by the electrochemical analyzer and the corrosion potential and current were solved by Tafel's technique. And the mass of samples before and after 10 days immersion into hydrogen peroxide was also measured by precise balance, and the optimized experiment resulted in decreasing significantly the rate of mass loss after PIII treatment.The morphology of samples, including implantation, electrochemical corrosion and hydrogen peroxide oxidation, are characterized by scanning electron microscope (SEM), and four classical corrosion behavior are detected, i.e. grain boundary corrosion, location corrosion, location and pit corrosion, and pit corrosion. Furthermore, the conclusion that whether the grain boundaries or the matrix is chemically attacked may be determined by the balance between the degree of defects density at grain boundaries and at matrix was deduced. TiNx and TiO2 were detected respectively for the samples modified by nitrogen-PIII and oxygen-PIII by X-ray photoelectron spectroscopy (XPS). In addition, the trivalent titanium and the Ti-OH complex were also found. Furthermore, the basic reactions were suggested after immersion into hydrogen peroxide on the surface of Ti6Al4V modified by PIII.In summary, the oxidation can not be prevented on the implantation layer, because many defect structures, such as vacancies, dislocations and reduced species, were created on the surface of the alloy by the ion bombardment, ion irradiation. However, the diffusion rate of atoms can be decelerated when they cross the modified layer, and the utilization period can be expanded at condition of oxidizer, as long as the PIII technique is employed by proper parameters.