【作者】 刘兵；

【导师】 陈铮；

【作者基本信息】 西北工业大学 ， 材料学， 2002， 博士

【摘要】 针对目前电场作用研究中的问题，本文以铝合金为研究对象，分别在三个不同尺度的理论范畴：单原子的电子理论，多原子（原子团簇）的微观局域效应，和材料宏、微观行为，系统的、多层次的研究了电场在电子层次，溶质行为，微观组织，以及宏观的断裂特征和性能等多个尺度的电场效应。 在理论上，基于Thomas-Fermi理论，重点研究了电场作用对原子体系的内势场边界的影响，建立了外场作用下的原子势场外边界条件，并计算原子能量和压强；基于电子屏蔽模型，分析了电场作用下溶质行为的局域效应。在实验上，利用DSC热分析技术，分析了电场作用对Al-Li合金相析出动力学的影响；采用能谱成份检测，透射电镜和扫描电镜等多种微观检测手段，对铝合金的析出相，断裂特征、合金电导率和维氏硬度等性能在电场作用下的变化进行了系统的研究，并观察了Al-Cu共晶合金在电场作用下的凝固组织。 通过理论和实验的研究得到以下结果： 基于Thomas—Fermi方程，确定外势场对体系边界条件的影响，首次建立电场作用下的原子外边界条件。计算外势场影响下的合金体系的原子能量和原子边界压强，原子的能量和压强在正的外势场作用下随着势场强度升高而增加，在负的外势场作用下呈先降低后升高的趋势。铝、锂和铜原子的能量及压强在正、负外势场作用下的极值点不同。 能谱成份检测显示，电场固溶后含铜未溶相的数量和体积减少，未溶相多数为合金元素构成。电场固溶后元素检测结果显示，电场提高了Cu元素的固溶度，促进了Cu元素的均匀分布。电子屏蔽理论分析表明，电场作用增大了溶质在晶内的固溶能力。 首次对电场作用后合金的析出动力学研究，DSC测量分析表明，电场固溶对铝锂合金δ’相析出动力学影响不大，δ’相的析出百分数和析出速率变化不明显。而T₁相在电场固溶后最大析出温度后移，析出百分数降低，最大析出速率延迟。相析出激活能的计算表明，δ’相激活能升高较小，T₁相的析出激活能明显的升高。在正、负电场作用后的DSC热分析具有类似的结果。 TEM结果显示，正负电场作用下铝锂合金的δ’析出相形貌具有相同的变化规律。电场固溶对铝锂合金中δ’目的形貌和分布影响不大，电场时效促进δ’相的长大，增加其尺寸均匀性。电场固溶和时效均减小了PFZ的尺寸。电场固溶促进β’一相析出，合金中6相的和T；相的交互作用增强，且厂相和各相的复合相增多。 对铝理合金SEM实验发现，电场固溶和时效强化了晶界，和晶内塑性的改善，断裂特征出现由分层沿晶断裂向塑性断裂转变，断面塑性变形特征增加。同时提高了合金伸延伸率，而强度值基本不变。电场处理后的晶界处主要合金元素的分布没有改变。对电场处理后亚晶界的TEM研究表明，电场作用促使亚晶界模糊，亚晶界上位错穿越增多。 LY12合金在电场作用下表现出和铝理合金类似的组织和性能的变化规律：合金的强度值升高不明显，塑性在电场固溶和时效下有较大的提高；在断裂特征上表现为韧窝增加。对电场正、负极性的研究表明，两种电场作用具有类似的效应和规律。 首次系统研究铝理合金的显微硬度和电导率，发现电场作用提高了合金的显微硬度，电导率变化较小。合金硬度和电导率在电场作用下呈现新的对应关系，无电场作用时，电导率和维氏硬度对应增长，而电场固溶后，硬度随着电导率的增长而降低。正、负电场的作用具有相似的规律。 首次研究了静电场对共晶合金凝固的影响，静电场作用增加了铝铜二元共晶合金的晶粒大小和片层间距，减少了共晶晶粒数。电场没有造成试样表面成份的偏聚。正、负电场对凝固过程具有相同的影响规律，但正电场的效应要强于负电场的效应。更多还原

【Abstract】 The influence of a static electric field was investigated systemic in three stratifications: the electron scope of single atom, multi-atom local effect and macro-materials character based on electron theory. The multi-scope effect of electric field on metals and alloys, such as the atomic energy, solute elements, microstructure and precipitates, fracture character, mechanic and physical properties, were studied with the purpose of finding the mechanism and the nature of the electric field.Based on Thomas-Fermi theory, the effect of external electric field on atomic inner boundary potential was studied. The new atomic potential boundary condition with the influence of external electric field was established and the atomic energy and pressure were calculated with new boundary condition. The local effect of solute element under an electric field was analyzed with the electron shield model. In experiment, the DSC technique was used to analyze the effect of electric fields on the precipitate kinetic of Al-Li alloy solutionized with electric fields. The Energy spectrum, TEM and SEM techniques are employed to investigate the elements solution, precipitates, fracture character, conductivity and Vickers hardness. Also, the solidification of Al-Cu eutectic alloy was conducted with the influence of electric fields.Some new results and effects were got:Based on Thomas-Fermi theory, the influence of external electric field on atomic boundary potential is analyzed, and new boundary condition of atomic inner potential is presented. The calculation results show that the atomic energy and pressure increase with the positive external electric potential, but decrease first and then increase with negative potential. There is an extremum of the atomic energy and pressure. But the extremums are different to Al, Cu, and Li element.The Energy spectrum detect results show that electric field promotes the solution of Cu element and well distribution, and accelerates the dissolution of undissolved-phase containing Cu. The electron shield theory analysis shows that the electric field improves the solute solubility.The DSC results show that the electric fields have little influence on 8’ precipitation of Al-Li alloy. There is little change of the 8’ precipitate fraction and rate. But the Tj phase maximum precipitate temperature increases, the precipitate fraction decreases andVIIthe precipitate rate retards. The calculation shows that the 8’ precipitate activation energy changes little but increases for Tj phase. The positive and negative electric fields have the same effects.The TEM results show that the electric fields applied during solution have little influence on precipitation of 8’ phase of Al-Li alloy, but electric fields applied in aging accelerate the 8’ precipitation. The electric fields decrease the size of PFZ and promote the precipitation of p’ phase. The interaction of 8’ and T, phases is improved and the composite phase of 8’ and P’ increase. Both positive and negative electric fields have the similar effects.The electric field strengthens the laminate boundary of 2090 alloy. The laminate strengthening mechanism translates into boundary strengthening and grain inner toughening with more ductility fracture and less intergranular fracture. The ductility property is enhanced with no change of intensity. The main elements distribution has no change and the TEM results show that subgrain boundary is blurred with more dislocation.The electric fields have the same effect on LY12 alloy as to 2090 Al-Li alloy with enhanced ductility and more toughness socket on fracture surface. Both positive and negative electric fields have the similar effects.The Vickers hardness is enhanced but the conductivity change little. A new relationship of Vickers hardness and conductivity is got: the Vickers hardness increases with conductivity without electric field, but decreases with electric field with the influence of electric fields. Both positive and negative electric fields have the similar effects.The el更多还原