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摘要本文在室温下对具有双相晶体结构的钛合金Ti-6Al-4V进行宏观和微观的实验研究。首先，本文讨论了单轴棘轮实验过程中的循环软/硬化、所施加的平均应力和应力幅值的影响。在Ti-6Al-4V钛合金的宏观实验中存在明显的循环软化现象，以及依据棘轮应变率划分的棘轮效应演化的三个阶段。棘轮变形的发生很大程度上依赖于所施加的平均应力和应力幅值，棘轮应变随着所施加的平均应力和应力幅值的增加而增加。然后，本文通过透射电子显微镜对Ti-6Al-4V钛合金单轴棘轮演化过程中的位错模式和孪生变形进行了观察，观察显示孪生变形主要发生在α主相，并且其变形单元的数量是伴随着棘轮演化过程递增的。同时材料的位错线也随着周次的增长，由散布演化为网状。α主相中的孪生变形是Ti-6Al-4V钛合金单轴棘轮效应发生的主要原因之一，在建立相应的结构本构关系时必须予以考虑。30428
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关键词：Ti-6Al-4V 棘轮效应 位错模式 孪生 单轴棘轮载荷
毕业论文设计说明书外文摘要
Title：Macroscopic and microscopic investigations on uniaxial ratchetting of two-phase Ti–6Al–4V alloy
Abstract
The uniaxial ratchetting of Ti–6Al–4V alloy with two phases (i.e., primary hexagonal close packed (HCP) α and secondary body-centered cubic (BCC) β phases) was investigated by macroscopic and microscopic experiments at room temperature. Firstly, the effects of cyclic softening/hardening feature, applied mean stress and stress amplitude on the uniaxial ratchetting of the alloy were discussed. The macroscopic investigation of Ti–6Al–4V alloy presents obvious strain-amplitude-dependent cyclic softening, as well as a three-staged evolution curve with regard to the ratchetting strain rate. The ratchetting depends greatly on the applied mean stress and stress amplitude while the ratchetting strain increases with the increasing applied mean stress and stress amplitude. Then, the evolution of dislocation patterns and deformation twinning during the uniaxial ratchetting of two-phase Ti–6Al–4V alloy were observed using transmission electron microscopy (TEM). The microscopic observation shows that deformation twinning occurs in the primary α phase and its amount increases gradually during the uniaxial ratchetting. Simultaneously, the planar dislocation evolves from discrete lines to some dislocation nets and parallel lines with the increasing number of cycles. The deformation twinning in the primary α phase is one of main contributions to the uniaxial ratchetting of Ti–6Al–4V alloy, and should be considered in the construction of corresponding constitutive model.
Keywords： Ti–6Al–4V Ratchetting Dislocation pattern Twinning Uniaxial cyclic loading
目 次
1 绪论 1
2 钛合金Ti-6Al-4V的棘轮行为宏观实验研究 4
2.1 实验条件 5
2.2 单轴拉伸实验 6
2.3 应变控制循环实验 6
2.4 应力控制循环试验 7
3 钛合金Ti-6Al-4V的棘轮行为微观实验研究 11
3.1 光学显微镜观察 11
3.2 透射电子显微镜观察 13
结论 22
致谢 23
参考文献24
第一章 绪论
1.1 研究意义
Ti-6Al-4V钛合金作为一种新兴的金属结构材料，在航空工业以及石油行业运用广泛，随着这些行业的迅速发展，这种合金的高比强度，良好的延生性、高温性能，抗腐蚀性展现出了独特的优势，合金构件部分替代了塑料、铝合金材料，从各方面看都很有可能成为一种非常重要的商用轻质金属材料。作为这些领域里的结构材料，Ti-6Al-4V经常会受到非对称的循环应力/应变作用，这种加载下的棘轮效应不断累积，对构件的可靠性和疲劳寿命有很大的影响，在工程结构设计时，是必须重点考虑的因素。然而，棘轮效应是一种由二次变形引起的循环累积，要得出准确的棘轮效应预测是非常困难的。