【作者】 张玉彬；

【导师】 刘庆；

【作者基本信息】 清华大学 ， 材料科学与工程， 2009， 博士

【摘要】 大形变量冷轧金属镍及镍合金在退火过程中可以形成很强的立方织构,是作为二代高温超导基带的理想材料。对大形变量冷轧金属镍的再结晶及立方织构形成进行系统的研究具有重要的理论和实际意义。本文主要采用电子背散射衍射(EBSD)、显微硬度、电子通道衬度(ECC)等技术对经两种方式(普通冷轧和累积叠轧(ARB))大形变量轧制金属镍的形变组织及退火过程中组织结构演变进行了系统的研究;并采用Monte Carlo点阵模型对晶粒长大过程中立方织构演化进行了系统的模拟。研究结果如下:(1)对再结晶初期的微观组织结构内不同取向晶核的来源分析表明立方取向晶核主要来源于形变组织内的立方取向带,而由立方孪晶取向晶粒通过孪生形成的几率较低;强立方织构的形成需要立方取向的形核率占总形核率的1/6~1/4左右。(2)对再结晶过程中不同取向晶粒的长大过程的定位观察研究表明,在整个再结晶过程中立方取向晶粒相对于非立方取向晶粒均有一定的长大速率优势,其原因是立方取向与形变基体间形成具有<111>转轴的大角晶界的几率较其它取向晶粒高。(3)采用Monte Carlo点阵模型对晶粒长大过程中立方织构演化进行模拟的结果表明,完全再结晶后微观组织结构内的立方织构体积分数越高、立方与非立方平均晶粒尺寸比越大,则立方织构含量随晶粒长大增长速率越快;并根据模拟结果建立了反映结构参数关系的图表,预测立方织构含量变化。(4)对再结晶过程中每个再结晶晶粒与其长大过程中吞并的形变组织之间的取向差的统计分析表明,再结晶过程中发生了移动和未发生移动的再结晶晶界的取向差分布没有本质的区别;并进一步阐明了动-停-再动的晶界移动方式是再结晶晶界移动的特有方式,进而说明晶界移动速率公式v=MF对局部再结晶晶界片段并不适用。(5)对Σ3晶界的结构特征和移动性研究表明Σ3晶界主要可以分成两种类:孪晶型和非孪晶型;二者可以通过单一参数(界面取向差与60°<111>的偏差角Δθ)来区分;非孪晶型Σ3晶界移动性远大于孪晶型Σ3晶界。更多还原

【Abstract】 Nickel and its alloys are ideally suited as substrate materials for second generation superconductors due to the fact that cold rolling to high strain followed by high temperature annealing results in formation of a very sharp cube texture in these materials. Research into the recrystalllization of highly cold rolled nickel and into the formation of the cube texture, therefore, is important for both theoretic understanding and practical application.In the present work the deformed microstructures and microstructural evolution during annealing of pure nickel highly deformed by both conventional rolling and accumulated rolling bonding have been systematically investigated using range of experimental techniques including electron backscattered diffraction (EBSD), micro-hardness measurement and electron channeling contrast . Furthermore a Monte Carlo Potts model was developed and used to systematically simulate the cube texture evolution during grain growth.The main conclusions achieved are as follows: (1) Analysis of the origin in samples annealed at a low temperature for a short time indicates that cube-oriented grains are mainly developed from cube-oriented deformation bands, but a few also develop from twinning of near cube-twin oriented grains. The formation of a sharp cube texture requires that the fraction of cube nuclei (number per unit volume) is higher than 1/6~1/4 of the total nuclei. (2) Results of“in-situ”experiments on the recrystallization process indicate that on average cube-oriented grains grow faster than other grains through the whole recrystallization process, mainly due to the fact that cube-oriented grains have a higher chance than other grains to encounter high-angle boundaries with misorientation rotation axes near the <111> corner. (3) Monte Carlo Potts model simulations of grain growth show that a higher of cube volume fraction (Fcube) and a higher ratio (β) of average grains size for cube-oriented grains compared to non-cube oriented grains in the fully recrystallized microstructure results in a faster the increase of the cube volume fraction. The diagram of Fcube-β-X has been established to show the connection between the structure parameters and to predict the cube volume fraction after grain growth. (4) A sequential annealing investigation of the relationship between each recrystallizing grain and the deformed matrix consumed by each grain during annealing indicates that the misorientation distributions for migrating and non-migrating recrystallizing boundaries are similar. Analysis of the data shows that the jerky movement is typical for recrystallizing boundaries and suggests that simple v=MF formulation does not hold for local recrystallizing boundary segments. (5) A detailed analysis of theΣ3 boundaries formed during recrystallization shows that theΣ3 boundaries can be separated into two groups: twin type and non-twin type. These can be differentiated using the total deviation parameter of each near-Σ3 boundary to the ideal 60°<111> relationship. The mobility for non-twin type ofΣ3 boundaries is substantially higher than that for twin typeΣ3 boundaries.更多还原