冷变形工业纯钛T40板材微观组织和晶体学特征的研究

发布时间：2018-11-16 13:48

【摘要】：钛及其合金由于具有良好的力学、化学及生物学性能,在航空航天、交通运输、军工军事、生物医疗及化工生产等领域都具有非常重要的应用价值。因此钛及其合金一直是材料科学领域研究的热点,研究者们对钛及其合金开展了广泛的研究,希望通过对显微组织结构演变规律和机理的研究进一步提高和改善其性能。如何提高钛及其合金的塑性及其成型性一直以来是一个亟待解决的问题,目前改善钛及其合金室温变形能能力的主要障碍在于对钛及其合金的变形机制了解不全面,对孪生的形成、长大及消失的解释众说纷纭；对孪晶机制和位错机制之间相互的协调和竞争还缺乏系统的、全面的认识,目前对两者之间相互作用的研究主要集中在计算机模拟方面,缺少实验上可见的证据和有力的理论解释。因此,对钛及其合金室温塑性变形机理的实验研究成为了该领域关注的焦点。针对上述问题,本工作选用工业纯钛T40板材为研究对象,采用扫描电镜-背散射电子衍射技术(SEM-EBSD)对冷轧过程中晶粒的形状、尺寸、晶体学取向以及孪晶出现顺序信息分别进行了表征和分析。通过建立简化模型,计算了形变孪晶变体的施密特因子、孪生应变以及孪晶生长过程中的塑性变形能,总结了形变孪晶变体选择的规律,探讨了影响形变孪晶变体生长的因素,解释了孪晶变体数目和其所在晶粒尺寸与晶粒形状之间的关系,阐明了形变孪晶变体选择的机理,预测了晶粒内孪晶系统选择和孪晶变体的生长情况。另外,本工作还采用准原位扫描电镜-电子背散射衍射技术(SEM-EBSD)表征了工业纯钛T40板材承受拉伸载荷过程中微观组织结构与晶体学取向的演化信息,分析了孪晶和位错滑移的形貌、出现顺序和出现位置,发现了在局部区域滑移和孪晶变形模式之间互相协调的现象,从材料连续的角度建立了与变形模式具有物理联系的切变位移梯度模型,研究了滑移和孪生之间的协调关系,实验验证了模型的合理性,解释了滑移和孪生变形模式之间互相激发、互相协调的原因,并进一步阐述了局部变形状态和宏观加载状态的共同作用下孪晶产生、生长及消失等演化过程的规律和机理。由于工业纯钛存在弹性各向异性,使得工业纯钛晶体中位错应变场形式非常复杂,在采用透射电镜鉴定位错的实验中,难以仅凭衍衬象衬度不可见条件来确定位错性质。出于对变形中位错鉴定的实际需求,我们基于晶体学理论提出了一种鉴定位错的计算方法,此方法可以明显简化透射电镜位错鉴定过程,通过对工业纯钛中位错的鉴定我们验证了该方法的可行性和准确性,此计算方法的使用对TEM位错鉴定具有指导意义。以上工作从微观尺寸上对进一步深化钛合金变形行为和机理的认识进行了理论补充,对计算机模拟工作提供了实验参数和实验依据,为钛合金的设计优化、性能预测和失效控制等奠定了理论基础。
[Abstract]:Titanium and its alloys have very important application value in the fields of aerospace, transportation, military, biological and chemical production because of good mechanical, chemical and biological properties. As a result, the titanium and its alloys have been a hot spot in the field of material science, and the researchers have conducted extensive research on the titanium and its alloys, hoping to further improve and improve the performance of the microstructure evolution law and mechanism. how to improve the plasticity and formability of titanium and its alloys has been a problem to be solved, and the main obstacle to improve the ability of titanium and its alloy at room temperature is that the deformation mechanism of titanium and its alloy is not comprehensive, and the formation of twinning is not complete. There is a lack of systematic and comprehensive understanding of the mutual coordination and competition between the mechanism of the crystal and the mechanism of the dislocation, and the research on the interaction between the two is mainly focused on the computer simulation. The lack of experimental evidence and a strong theoretical explanation. Therefore, the experimental study on the mechanism of the plastic deformation of the room temperature of the titanium and its alloy has become the focus of attention in this field. In the light of the above problems, the industrial pure titanium T40 plate is used as the research object, and the shape, the size, the crystallographic orientation and the order information of the crystal grain in the cold rolling process are characterized and analyzed by using the scanning electron microscope-backscattering electron diffraction (SEM-EBSD) technique. By establishing a simplified model, the Schmitt factor, the twin strain and the plastic deformation energy in the process of crystal growth are calculated, the law of the choice of the deformation and the crystal variation is summarized, and the factors that influence the growth of the deformed crystal are discussed. The relationship between the number of the crystal grains and the grain size and the grain shape of the crystal grain is explained. The mechanism of the choice of the crystal grain is explained, and the selection of the crystal grain and the growth of the crystal grain are predicted. In addition, a quasi-in-situ scanning electron microscope-electron backscatter diffraction (SEM-EBSD) technique was used to characterize the evolution of the microstructure and crystallographic orientation of the industrial pure titanium T40 plate in the process of tensile loading, and the morphology, appearance and location of the crystal and dislocation slip were analyzed. In this paper, a shear displacement gradient model with physical contact with the deformation mode is established from the continuous angle of the material and the coordination relation between the slip and the twin is studied, and the rationality of the model is verified. The causes of mutual excitation and mutual coordination between the slip and twin deformation modes are explained, and the rules and mechanisms of the evolution of the generation, growth and disappearance of the columnar crystal under the co-action of the local deformation state and the macroscopic loading state are further described. Because of the elastic anisotropy of the industrial pure titanium, the form of the dislocation strain field in the industrial pure titanium crystal is very complicated. Based on the theory of crystallography, a method for identifying the dislocation is proposed, which can be used to simplify the process of the dislocation identification of the transmission electron microscope. The feasibility and the accuracy of the method are verified by the identification of the dislocations in the pure titanium. The use of this method is of great significance for TEM dislocation identification. The above work is a theoretical supplement to the understanding of the further deepening of the deformation behavior and mechanism of the titanium alloy from the micro-scale, and provides the experimental parameters and the experimental basis for the computer simulation work, and lays a theoretical foundation for the design optimization, the performance prediction and the failure control of the titanium alloy.
【学位授予单位】：东北大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.23

【相似文献】