【作者】 辛国强；

【导师】 田修波；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2007， 硕士

【摘要】 Ti6Al4V具有良好的力学性能,其比重小,比强度高,有着广泛的应用领域。但是,该合金硬度低,耐磨性能差,并且化学活性高。当它与氧化性溶液(如双氧水等)接触后,由于合金的双相结构极易形成腐蚀原电池,加速氧化腐蚀过程,使零件过早的失效。因此,延长钛合金在氧化性氛围中的使用寿命,越来越受到人们的关注。本文采用等离子体浸没离子注入(PIII)技术,在Ti6Al4V合金表面制备一层改性层,用来提高该合金的抗氧化腐蚀性能。采用正交试验系统研究了注入电压、射频功率、注入气压、注入时间、注入元素种类五个注入参数对改性后Ti6Al4V的机械性能、电化学腐蚀性能、抗氧化化性能的影响。在此基础上,进一步研究了氮气注入条件下,注入气压单参数变化对改性后Ti6Al4V性能的影响规律,以及氧气注入条件下,注入时间单参数变化对改性后Ti6Al4V性能的影响规律。采用超小载荷显微硬度计测量试样改性后的显微硬度值,结果表明经过离子注入后试样的显微硬度均较基体提高。利用自制球盘式摩擦磨损试验机测量试样的摩擦系数,并且利用积分摩擦系数来表征材料的耐磨性能。采用电化学腐蚀测试仪测量改性层腐蚀极化曲线,根据塔菲尔(Tafel)外推法计算改性层的腐蚀电位、腐蚀电流,来表征改性层的电化学腐蚀性能。用精密天平称量双氧水浸泡10天前后的质量,计算单位质量损失率来表征材料抗氧化腐蚀性能,优化后的试验结果证实,注入后试样质量损失均比基体减小。扫描电子显微镜(SEM)观察离子注入形貌、电化学腐蚀形貌、氧化腐蚀形貌,氧化腐蚀后观察到晶界腐蚀、均匀腐蚀、均匀腐蚀加孔蚀及孔蚀四种典型形貌。在上述分析的基础上,提出了晶界缺陷密度和晶粒缺陷密度决定的腐蚀形貌判据。采用X射线光电子谱(XPS)分析浸泡氧化腐蚀前后试样表面成分,表明注入后试样表面形成化合物,氮注入后试样形成了TiNx。氧注入试样形成了TiO2,同时在注入试样表面发现了三价的钛原子,浸泡后试样表面发现了Ti-OH化合物。在上述结果基础上,提出了改性层氧化腐蚀的基本化学反应过程。综上所述,由于离子轰击、辐照作用,给表面带来了空位、位错和还原原子等缺陷。等离子体浸没离子注入处理,并不能阻止氧化腐蚀的进行,但是在适当的工艺条件下,对原子扩散氧化起抑制作用,延缓材料的氧化腐蚀行为,提高材料在氧化性溶液中的使用寿命。更多还原

【Abstract】 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.更多还原