新型β钛基形状记忆合金的低周疲劳行为研究

发布时间：2018-01-21 21:51

  本文关键词： β钛基形状记忆合金 数字图像相关技术 疲劳 裂纹扩展　出处：《湘潭大学》2016年硕士论文　论文类型：学位论文

【摘要】：新型β钛基形状记忆合金具有对人体无潜在毒性、优异的超弹性和优良的生物相容性,作为植入体材料在生物医用领域有着极大的应用潜力。深入研究β钛基形状记忆合金低周疲劳性能以及显微组织对其疲劳性能的影响,并进一步探讨和分析在交变载荷作用下β基形状记忆合金马氏体相变过程,裂纹扩展与马氏体相变之间的交互作用及其机理,为推进该类合金实用化具有重要意义。本文以具有优异超弹性能的Ti-7.5Nb-4Mo-2Sn形状记忆合金为研究对象,利用数字图像相关技术对β基形状记忆合金变形进行原位观察,并研究其变形特性;对循环载荷作用下该合金的疲劳寿命进行了评估,分析了疲劳变形过程中显微组织、弹性模量和超弹性能变化规律;最后对裂纹扩展过程和裂纹尖端应变场动态演变过程进行DIC原位观察,分析α、β相界对裂纹扩展影响机理。主要研究内容和结论如下:(1)对Ti-7.5Nb-4Mo-2Sn合金在室温下进行扎制,在600℃到800℃下对合金进行退火处理,对不同退火温度下合金的显微组织、力学性能和变形特性进行研究,结果表明:α→β相的相转变点在700℃与800℃之间。700℃和800℃合金在室温下表现超弹性能。其中700℃处理得到的合金因其细小的组织结构和α相强化作用,表现出更加优异的超弹性能。马氏体相变起源于样品表面,然后向样品内部扩展,且扩展不均匀,向有利于马氏体相变的晶粒中扩展。(2)对不同退火温度处理后的800℃退火处理后的Ti-7.5Nb-4Mo-2Sn合金的低周疲劳寿命进行测试,结果表明:合金表现出比700℃处理后合金更高的疲劳寿命。形状记忆合金反复变形过程马氏体相变释放热量,合金温度升高,促进了β→α和β→ω相变过程。疲劳变形过程中,合金发生了先软化后硬化现象。合金软化是由于孪生合并引起的;合金后来硬化是由于疲劳次数的增加,α和ω两相含量越来越高的缘故。(3)采用数字图像相关方法(DIC)对Ti-7.5Nb-4Mo-2Sn合金在加载过程中裂纹扩展过程和裂纹尖端应变场进行原位观察。研究表明:相同加载速率下,与800℃退火处理后的合金相比,700℃退火处理的合金裂纹扩展速率和偏转角偏高,这与700℃退火处理的合金中含有大量α相有关,α、β相界易产生微裂纹或使得裂纹发生偏转。从应变云图可以看出在预制裂纹尖端产生应力集中,宏观上表现为变形不均匀,马氏体相变发生在变形较大处,裂纹沿着变形较大处扩展,马氏体相变阻碍裂纹扩展。
[Abstract]:The new 尾 -titanium-based shape memory alloy has no potential toxicity to human body, excellent superelasticity and excellent biocompatibility. As implant material, it has great application potential in biomedical field. The low cycle fatigue properties of 尾 -Ti based shape memory alloy and the effect of microstructure on its fatigue properties are studied in depth. Furthermore, the process of martensite transformation, the interaction between crack propagation and martensite transformation and its mechanism are discussed and analyzed under alternating load. In order to promote the practical application of this kind of alloy, the Ti-7.5Nb-4Mo-2Sn shape memory alloy with excellent superelastic properties is taken as the research object in this paper. The deformation of 尾-based shape memory alloy was observed in situ by digital image correlation technique and its deformation characteristics were studied. The fatigue life of the alloy under cyclic loading was evaluated, and the changes of microstructure, elastic modulus and superelastic energy during fatigue deformation were analyzed. Finally, the crack propagation process and the dynamic evolution of the strain field at the crack tip are observed in situ by DIC and the 伪 is analyzed. The effect of 尾 phase boundary on crack growth. The main contents and conclusions are as follows: 1) the Ti-7.5Nb-4Mo-2Sn alloy is bound up at room temperature. The alloy was annealed at 600 鈩，

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