超低弹性模量Ti-Nb基亚稳β钛合金的相变和力学行为

发布时间：2018-01-15 15:09

本文关键词：超低弹性模量Ti-Nb基亚稳β钛合金的相变和力学行为　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：钛及钛合金凭借其低弹性模量、良好的综合力学性能、生物相容性和耐腐蚀性而广泛应用在生物植入件上。然而,目前应用最广的钛和钛合金(如Ti-6Al-4V)的弹性模量约为110GPa,仍高于人骨的弹性模量(约为30GPa),由于植入件与人骨弹性模量的不匹配,在植入时容易诱发“应力屏蔽”效应。此外,Al和V的释放会导致长期的健康问题,如骨软化症和神经性疾病。因此,研发低模量、高强度且完全由无毒元素组成的新型β型钛合金已成为生物医用植入材料的研究热点。本文以低模量作为合金成分设计的主要依据,设计研制出Ti-33Nb-4Sn(wt.%)合金,并通过力学性能试验机(Mechanical Testing Machine)、X射线衍射仪(XRD)、透射电子显微镜(TEM)、原位同步辐射(in-situ synchrotron X-ray diffraction)和利用弹塑性自洽模型(EshelbyKroner-Kneer elastoplastic self-consistent model)等手段系统地研究了热机械处理对新型Ti-Nb-Sn合金相变、微观结构和力学行为的影响,旨在开发出低模量和高强度兼备的亚稳β型钛合金,并揭示其低模量机制和变形行为的物理机制,为新型低模量高强度钛合金的设计提供理论指导。研究结果表明:本文设计研制的Ti-33Nb-4Sn(wt.%)合金,固溶态合金由β和α?马氏体两相组成,冷轧处理后合金的相组成仍为β和α?马氏体,冷轧变形后的合金经425℃时效处理30min后,合金主要由β相组成,同时含有少量的细小α相,合金抗拉强度为855MPa,弹性模量为36GPa。TEM结果表明,冷轧和短时时效处理过程中引入的高密度位错、细化晶粒和纳米尺度的α相共同作用,赋予合金高的强度,此外由于时效处理时间较短,仍保持具有本征低模量的β相,同时α相的形成量很少,不足以显著提高合金模量,因此合金模量较低。由此获得合适的热机械处理制度,即冷轧短时时效处理能够使合金兼具高强度和低模量。为探究其低弹性模量机制的本质,我们利用弹塑性自洽(EPSC)模型结合同步辐射技术计算出合金的单晶弹性常数,发现低模量Ti-33Nb-4Sn合金具有与同等价电子浓度(e/a)的二元合金相当的C?(12.6GPa)以及明显偏低的C44(22.4GPa),基于此我们推断,通过热机械处理得到的亚稳β型钛合金,其具有较低的剪切模量C?和异常偏低的剪切模量C44,两者共同作用可获得低弹性模量。同时为了研究其变形行为的物理机制,我们尝试利用同步辐射技术将材料的变形行为与细微的结构转变建立起联系,发现固溶态合金在拉伸过程中出现“双屈服”现象的原因是由于马氏体变体的再取向和应力诱发马氏体相变,Ti-33Nb-4Sn合金经冷轧处理后,合金中存在的大量位错和晶界能够对马氏体切变产生明显阻碍作用,因此冷轧态合金在拉伸过程中应力诱发马氏体相变的程度明显小于固溶态合金,其在拉伸过程中呈现出“非线性”变形。而冷轧短时时效态合金在变形行为中比固溶态和冷轧态的合金都要稳定,是因为经冷轧短时时效处理后合金中高密度位错、晶界和纳米尺度的α相对抑制拉伸行为中应力诱发马氏体相变起到了重要作用,因此其宏观拉伸应力应变曲线在弹性阶段呈现出与常规材料一致的“线弹性”变形。
[Abstract]:Titanium and titanium alloy with low elastic modulus, good mechanical properties, biocompatibility and corrosion resistance and is widely used in the biological implant. However, currently the most widely used titanium and titanium alloys (such as Ti-6Al-4V) the elastic modulus is about 110GPa, is still higher than the human bone elastic modulus (ca. 30GPa), due to the mismatch of implant and bone elastic modulus, easy at implantation induced by stress shielding effect. In addition, Al and V release will lead to long-term health problems, such as osteomalacia and neurological diseases. Therefore, developing new low modulus, high strength titanium alloy which is entirely non-toxic elements has become a research hotspot of medical implant material. In this paper, a low modulus as the main basis of composition design, design and development of a Ti-33Nb-4Sn (wt.%) alloy, and the mechanical performance testing machine (Mechanical Testing Machine), X ray diffraction Radiometer (XRD), transmission electron microscopy (TEM), in situ synchrotron radiation (in-situ synchrotron X-ray diffraction) and using the elastoplastic self consistent model (EshelbyKroner-Kneer elastoplastic self-consistent model etc.) were studied by means of thermo mechanical treatment on phase transformation of new Ti-Nb-Sn alloy, microstructure and mechanical behavior, in order to develop metastable beta titanium alloy with low modulus and high strength both the physical mechanism and reveal the mechanism of low modulus and deformation behavior, provide theoretical guidance for the design of new low modulus and high strength titanium alloy. The research results show that the design and development of Ti-33Nb-4Sn (wt.%) alloy, solid solution alloy by beta and alpha martensite phase? Composition, phase composition of cold treated alloy is beta and alpha? Martensite after cold rolling alloy is 425 DEG C after aging treatment of 30min alloy is mainly composed of beta, phase composition, and contains a small amount of The small phase, the tensile strength of the alloy is 855MPa, the elastic modulus is 36GPa.TEM. The results show that the high density of dislocation introduced by cold rolling and short-time aging process, refine grain and nano scale alpha phase interaction, with high strength alloy, due to aging treatment for a short time, still has the character of low modulus the beta phase, while alpha phase formation very small, not enough to significantly improve the modulus of alloy, so the alloy of low modulus. The thermal mechanical treatment system, which can make the alloy cold rolling short-term aging treatment with high strength and low modulus. For its inquiry into the nature of low elastic modulus mechanism, we use elastic plastic self consistent (EPSC) model combined with the calculated elastic constants of alloy single crystal synchrotron radiation technology, found that low modulus Ti-33Nb-4Sn alloy with the same equivalent electron concentration (e/a) of the two element alloy equivalent C (12.6GPa) and obvious? Low C44 (22.4GPa), based on this we conclude by thermo mechanical treatment of metastable beta titanium alloy is obtained, which has low shear modulus C and shear modulus C44? Abnormally low, both can obtain low elastic modulus. At the same time in order to study the deformation behavior of the physical mechanism, we tried to use synchronization radiation technology will change the deformation behavior of materials with fine structure to establish contact, find solid solution alloy in tensile process in a "double yield" phenomenon is due to martensite reorientation and stress induced martensitic phase transformation of Ti-33Nb-4Sn alloy after cold rolling process, a large number of dislocations and grain boundaries exist in the alloy can produce obvious effects on the martensitic shear, therefore cold-rolled alloy stress induced martensitic transformation significantly less than solid solution alloy during the stretching process, the tensile process in "Nonlinear" deformation. And cold rolled alloy in short always effect the deformation behaviors than alloy solid solution and cold rolling are stable, because the high dislocation density in the alloy after cold rolling and short-time aging treatment, grain boundary and nano scale alpha relative inhibition tensile behaviour in the important role of stress induced by Ma's transformation, so the macro tensile stress-strain curve in the elastic stage shows with conventional materials with the "elastic" deformation.

【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.23

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