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1、高压扭转纯铝的境界结构研究摘 要与粗晶材料相比，超细晶纳米晶材料凭借其极细的晶粒尺寸而具有一系列优异的力学性能和物理化学性能。密集的晶界是细晶材料具有高性能的主要原因。大塑性变形(SPD) 是一种有效的制备超细晶纳米晶材料的方法。大塑性变形以块体材料为对象，通过对其进行剧烈塑性变形而引入极高的应变量，引起位错增殖等微观结构的演变，从而在不改变样品尺寸的前提下制备出超细晶纳米晶材料，而且用 SPD 制备的材料内部无孔洞、夹杂等缺陷。其中，高压扭转(HPT) 是细化粗晶材料能力最强的一种 SPD 技术。HPT 过程中，圆片状试样在极高的压力下进行剪切变形，获得具有大角度晶界的纳米晶材料。同时结合E
2、BSD研究手段分析高压扭转纯Al的微观组织和晶界结构。得到的主要结论如下：(1) 微观组织表征表明高压扭转处理可以显著的降低纯Al的晶粒尺寸，并不断增加位错数量。如将高压扭转纯铝的X射线衍射数据输入Jade，统计的平均晶粒尺寸为164 nm，位错密度为0.161014 m-2，通过TEM截线法12测得高压扭转纯Al的平均晶粒尺寸为381nm，通过HRTEM计算选区内的位错密度为2.27 1016 m-2。(2) EBSD结果表明：1）高压扭转处理后的晶粒大小分布不均匀，但多数晶粒尺寸小于1000nm； 2) 纯铝高压扭转变形后， 29的晶界比例远高于 值大于29的晶界比例，在所有 29的晶界中
3、，3晶界所占比例最高，其次是9晶界； 3) 反极图(IPF)结果表明高压扭转后纯铝的多数晶粒沿、三个方向分布，可以认为这是由于剧烈塑性变形在纯铝中产生具有方向性的织构所导致；4）再结晶分布图和应力分布图表明表明高压扭转过程中发生了再结晶现象，部分晶粒长大并在纯铝的晶粒内部引入了残余应力（3）力学性能结果表明高压扭转可以提高纯铝的强度和硬度。高压扭转前后硬度从30 HV增加到71 HV，高压扭转纯Al试样硬度是高压扭转之前的2.35倍。在高压扭转处理前，纯铝试样的屈服强度和抗拉强度为45 MPa和75 MPa，经过高压扭转处理之后，试样的屈服强度和抗拉强度增加到145 MPa和200 MPa，高
4、压扭转纯Al的屈服强度是未高压扭转处理之前的3.2倍，抗拉强度是未处理之前的2.7倍。关键词：高压扭转，纯铝，透射电子显微镜，微观结构，力学性能，晶界结构Study on the Boundary Structure of High Pressure Torsional Pure AluminumAbstractCompared with coarse-grained materials, ultrafine-grained nanocrystalline materials have a series of excellent mechanical properties and physic
5、al and chemical properties due to their very fine grain size. Dense grain boundaries are the main reason for the high performance of fine grained materials. Large Plastic Deformation (SPD) is an effective method for preparing ultrafine crystalline nanocrystalline materials. Large plastic deformation
6、 takes bulk materials as its object. By introducing extremely high strain due to severe plastic deformation, dislocation proliferation and other microstructural evolution can be induced. Ultrafine nanocrystalline materials can be prepared without changing the size of samples. Moreover, there are no
7、defects such as voids and inclusions in the materials prepared by SPD. Among them, high pressure torsion (HPT) is the most powerful SPD technology to refine coarse grained materials. In the HPT process, the wafer specimen was sheared under extremely high pressure to obtain nanocrystalline materials
8、with large angle grain boundaries. At the same time, the microstructure and grain boundary structure of pure Al under high pressure torsion were analyzed by means of EBSD. The main conclusions are as follows:(1) The characterization of microstructure show that high pressure torsion can significantly
9、 reduce the grain size of pure Al and increase the density of dislocations.Input the X-ray diffraction data into Jade, it can be calculated that the average grain size is 164 nm and the dislocation density is 0.161014 m-2. TEM analyses show that the average grain size of pure Al is 381nm .HRTEM obse
10、rvation indicate that the dislocation density in the selected area is 2.27 1016 m-2.(2) The EBSD results can be concluded as follows: 1) After high pressure torsion ,the distribution of grain sizes are not uniform but most grain sizes are less than 1000nm. 2) When processed by high pressure torsion
11、, the ratio of 29 grain boundary is much higher than that of 29 in pure aluminum. Of all the 29 grain boundaries , 3 grain boundary occupies the highest proportion, followed by 9. 3) The inverse pole diagram shows that the majority grains of pure aluminum are distributed in three directions: , , ,Wh
12、ich may be the reasons of directional texture caused by severe plastic deformation. 4) The diagram of recrystallization distribution and stress distribution show that recrystallization occurs in the process of high pressure torsion. (3) Mechanical tests show that high pressure torsion can improve th
13、e strength and hardness of pure aluminum.After the HPT process, the hardness value of pure aluminum increased from 30HV to 71 HV, which is 2.35 times of the undeformed value.Besides, the yield and tensile strength of pure aluminum increased from 45 MPa and 75 MPa to 145 MPa and 200 MPa, respectively
14、, which is 3.2 and 2.7 times of the undeformed value, respectively.Keywords: High pressure torsion; Pure aluminum; Transmission electron microscope; Microstructure; Mechanical properties; Grain boundary structure目 录第一章 绪论121.1 纯铝的特性和应用121.1.1纯铝及高纯铝的发展和分类121.1.2 纯铝的性能与应用141.1.3 超细晶纯铝材料的研究现状151.2 高压扭转
15、技术151.3 超细晶纳米晶材料的韧化181.3.1超细晶纳米晶材料的塑韧性181.3.2 超细晶纳米晶材料韧化方法201.4 SPD 的应用211.5 本课题的研究内容及意义23第二章 实验过程与分析方法242.1实验过程242.2 试样切割与高压扭转实验252.3 X射线衍射分析262.4 HPT 实验272.5 力学性能测试272.5.1 拉伸实验272.5.2 显微硬度282.6 X 射线衍射分析282.7显微组织分析292.8 HPT纯铝的热稳定性分析30第三章 高压扭转纯铝的微观组织及晶界结构303.1 HPT 纯铝的微观结构303.2 HPT纯铝的XRD分析333.3 HPT 纯铝端视模式下的HRTEM分析353.4 TEM与HRTEM分析363.5 HPT 纯铝的热稳定性393.5.1 超细晶纳米晶材料的热稳定性393.5.2 HPT 纯铝的 DSC 分析403.5.3 纯铝变形后的EBSD分析423.6 HPT纯铝的力学性能44第四章 结论与展望464.1 结论464.2 创新与展望46参考文献47第一章 绪论随着世界工业水平的不断进步，航空航天、军用器械、汽车产业等行业都提出了较高的材料性能要求。铝是广泛使
