【作者】 孙中刚；

【导师】 周文龙； 侯红亮；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2009， 博士

【摘要】 钛合金具有比强度高、质量轻、耐腐蚀等特点,在航空航天等领域上获得了较为广泛的应用。然而,钛合金室温塑性低、变形抗力大、冷成形容易开裂等缺点大大限制了其冷态工艺性。置氢加工技术是利用氢在钛合金中的可逆合金化、氢致塑性和氢致相变等作用,通过改变合金的相成分及组织进而改善钛合金加工性能的一种新工艺、新方法。利用氢致室温增塑效应实现钛合金的冷镦成形是置氢加工的重要应用之一,但是国内学者在这方面的研究较少。本文从氢致钛合金相变入手,系统地研究氢致室温增塑的氢处理工艺及室温增塑机理。利用OM、XRD、TEM等分析手段研究了氢TC4、TC16钛合金组织演变;设计了石英管封装的热处理试验装置,并借助此装置完成了金相法对置氢钛合金β相转变温度(T_p)的测定以及氢致亚稳相转变规律的研究,建立了TC4-H、TC16-H的亚稳相转变相图。研究表明:氢作为β相稳定化元素,降低了TC4、TC16钛合金的β相转变温度,促进了α″马氏体和亚稳β相的生成。但由于氢在两种合金中的有限固溶使得氢无法将两种合金的β相完全稳定至室温。尽管如此,合金中α″马氏体和亚稳β相的出现仍为氢致室温增塑提供了基础。根据氢对两种合金相转变的影响,确定了实现室温增塑的最佳热处理工艺为:T_p+10℃淬火。采用压缩、拉伸、夏比冲击和动态镦粗等实验系统研究了置氢对TC4钛合金室温动、静态变形行为的影响;利用OM、XRD、TEM手段分析了置氢后材料的室温变形机理。结果表明:TC4钛合金经过T_p+10℃淬火后,室温压缩极限变形率随着氢含量的增加而增加,氢含量在0.6～0.9wt%时,极限变形率较原始合金提高了近一倍。拉伸和冲击试验结果表明,无论哪一种处理方式,材料的综合性能均下降,产生脆断。微观组织观察和相分析表明,置氢TC4钛合金室温压缩增塑的机理为:①氢促进了合金中α″马氏体与亚稳β相的生成;②变形过程中产生应力诱发α″马氏体;③氢降低了位错与孪晶形成的临界应力;④淬火后氢化物以纳米级出现。采用静态压缩、拉伸,动态镦粗和霍普金森压杆试验等实验系统研究了置氢对TC16钛合金室温动、静态变形行为的影响,并建立了室温本构方程;利用OM、XRD、TEM手段分析了置氢合金室温变形的机理。结果表明:置氢后TC16钛合金的拉伸性能大幅度下降,产生脆断;静态变形时,随着氢含量的增加,极限变形率降低;动态变形试验表明,置氢合金具有较好的变形能力,氢含量为1.0wt%时,变形极限超过70%。微观组织观察和相分析表明,氢致TC16钛合金室温压缩增塑的机理为:①氢降低了TC16钛合金的相变点,提高了β相的稳定性;②快速变形下,绝热温升显著,氢降低了合金的高温流变应力;③氢降低了临界剪切应力促进了位错的增殖和孪晶的产生,并发生应力诱发马氏体相变。利用金相法研究了α″马氏体和亚稳β相的分解转变过程,并据此制定了TC4钛合金细晶强化及除氢的热处理工艺,研究了除氢后的力学性能。结果表明:α″马氏体和亚稳β相的时效分解属于扩散型相变,700℃时两相的分解孕育期最短,分解完成时间最少;氢促进了β相稳定化元素的扩散,在时效过程中优先析β相,并在除氢过程没有随着氢的除去而分解。除氢后力学性能测试表明:氢含量为0.45wt%时时效强化效果最好,但是0.8wt%时获得比较好的综合性能。更多还原

【Abstract】 Titanium alloys are widespread availability in aviation industry due to the high strength-to-weight and the resistant to corrosion. However, its low room temperature plastic, high resistance of deformation, and easily to crack during deformation limited the cold working properties. Thermohydrogen processing (THP), based on the modifying effect of hydrogen as an alloying element on phases and kinetics of phase transformation in titanium alloys, has been used as a new method to improve the mechanical properties of titanium alloys. Hydrogen induced cold plasticity is one of the mainly aspects, but the investigation on this aspects is little in national. Therefore, this work begins from the studying of hydrogen induced phase transformation, and then investigated the heat treatment for improve the cold forming and the mechanism of the cold deformation systematically.OM, XRD, TEM were utilized to investigate the effect of hydrogen on the microstructure evolution of TC4 alloys and TC16 alloys. A quartz tube device was designed and theβphase transition temperature of the hydrogenated titanium alloys was investigated using metallographic method by the device. The effect of hydrogen on the metastable phase transition was investigated and the corresponging TC4-H, TC16-H phase diagram were built, which establish the theoretical basis of the hydrogen treatment. The results showed that, as aβstabilizer, the addition of hydrogen decreased theβphase transition temperature of the TC4, TC16 alloys, promoted the formation of a" martensites and the metastableβphase. However, theβphase can not be stabilized completely to room temperature due to the limited solid solubility of hydrogen in titanium alloy. Even though, the appearance of the a" martensites and the metastableβphase still provide a basis for the improvement of cold deformation. According to the phase transition, the optimum for the improvement of cold deformation is quenching 10℃above theβphase transition temperatureThe compression test, tensile test, charpy impact test and dynamic upset test were conducted to investigate the dynamic and the static deformation behaviors of the hydrogenated TC4 alloys. OM, XRD, TEM were utilized to investigate the mechanism of the cold deformation. The results showed that the deformation limit of hydrogenated specimen increases with the increase of hydrogen concentration, and reaches maximum in specimen containing 0.6～0.9wt % H, nearly one times of the as-received. However, the results of the tensile test and the charpy impact test showed that the mechanical properties of hydrogenated alloy decreased and embrittled and shown no relationship with the treatment. According to the evolution of the microstructure after deformation, it can be concluded that the improvement of the cold deformation for TC4 alloy are owing to:①the addition of hydrogen promoted the formation ofα" martensites and the metastableβphase;②the stress induced martensites occurred during deformation;③hydrogen decreased the critical stress of the formation of dislocation and twins;④the formation of nano-structured hydrides.The compression tests, tensile tests, dynamic upset test and SHPB were conducted to investigate the dynamic and the static deformation behaviors of the hydrogenated TC16 alloys. OM, XRD, TEM were utilized to investigate the mechanism of the cold deformation. The results showed that the tensile properties decreased greatly after hydrogenation. Under the static deformation, the deformation limit decreased with the increase of the hydrogen concentration, while the alloy exhibited well deformation abilities under dynamic deformation, no crack occurred even upsetting to 70% in specimens containing 1.0wt %H. According to the evolution of the microstructure after deformation, it can be concluded that the improvement of the cold deformation for TC16 alloy are owing to:①the addition of hydrogen decreased theβtransition temperature and improved the stability of theβphase,②adiabatic temperature rise occurred during the fast deformation which supplied the conditions for hydrogen induced plasticity,③hydrogen decreased the critical stress of the formation of dislocation and twins and promoted the stress induced martensites occurred during deformation.Metallographic method was utilized to investigate the decomposition of theα" martensites and the metastableβphase, and according to the results the refining processing and the dehydrogenation heat treatment of the TC4 alloy were formulated. The results showed the decomposition of these metastable phases occurs by a nucleation and growth process controlled by atom diffusion and the shortest incubation of the decomposition is at 700℃, in which the decomposition time is shortest. The addition of hydrogen promoted the diffusion of theβstabilizer, resulting in the formation of the stableβphase, which finally retained in the alloy during the dehydrogenation. The mechanical properties of the alloy after dehydrogenation showed that specimens containing 0.45wt % H with full martensites after hydrogen treatment shows a high degree increase of strength. However, a fine grain and a comprehensive mechanical properties was obtain in specimens contains 0.8wt % H.更多还原