TbDyFe合金的定向凝固和取向生长

利用自制的超高温度梯度定向凝固装置,研究了稀土巨磁致伸缩材料Tb0.27Dy0.73Fex(x=1.8,1.95at%)合金在不同凝固条件下的凝固行为。发现Tb0.27Dy0.73Fe1.8合金在不同的凝固条件范围内可以有有序的层状结构、无序的短柱状结构和混合结构,而Tb0.27Dy0.73Fe1.95合金的显微结构始终是层片状结构,在实验条件范围内与凝固条件无关;分析了Tb0.27Dy0.73Fe1.95合金定向凝固条件、晶体生长形貌、晶体择优生长方向间的关系,发现结晶形貌为胞状晶或无侧向分枝的树枝晶时其择优取向为<110>,结晶形貌为发达的树枝晶时其择优生长方向为<112>,而在胞-枝转变区晶体为<110>,<112>,<113>等多种取向的混合,胞枝转变区随温度梯度的提高而减小;Tb0.27Dy0.73Fe1.95合金定向凝固时发生胞枝转变的凝固条件为GL/V值介于(9.60～10.45)×102K·s/mm2之间。     

Al-La合金不连续枝晶组织形成机理

在Al-La合金的自由凝固试样中,发现Al-35%La合金组织形貌的特殊性,其先结晶相Al11La3枝晶沿主干方向成分是不连续的. 为验证这种组织存在的真实性,采用定向凝固方法制备了不同冷却速度下的Al-35%La合金试样,结果显示出定向凝固Al-35%La合金中Al11La3枝晶沿主干方向成分是不连续的. 在此基础上,分析了化学成分与凝固速度对Al-La合金组织的影响,并初步探讨了这种不连续枝晶的形成机理.     

α-Al磁性对强磁场下Al-Cu亚共晶合金定向凝固组织的影响

以Al-Cu亚共晶合金为研究对象,考察了α-Al单晶磁各向异性对稳恒强磁场下定向凝固枝晶组织生长行为的影响.实验测定了α-Al单晶不同晶向的磁化率.结果表明:Al-Cu单晶中的磁化现象表现出明显的方向性;难磁化轴为晶体学位向111方向,即磁化率最小;易磁化轴为晶体学位向311或310方向,即磁化率最大;磁化率随Cu原子数量的增加而降低;[111]晶向族中4个晶向的磁化率不再一致.对于Al-0.85%Cu合金,当生长速度为50μm/s时,在无磁场情况下其定向凝固枝晶主干沿凝固方向排列;当施加6 T纵向强磁场时,枝晶主干偏离凝固方向成一定夹角排列,这一现象可能是由α-Al磁晶的各向异性所致.     

自适应有限元法对合金定向倾斜枝晶生长的相场法模拟

建立了合金定向倾斜枝晶生长的相场模型,采用非均匀网格的自适应有限元法求解薄界面层厚度条件下的相场模型,研究了Al-Cu(w(Cu)=4%)合金的倾斜枝晶演化过程,定量分析了冷却速率、主晶间距对凝固组织的影响.结果表明:冷却速率、主晶间距和抽拉速度可以控制倾斜枝晶的生长角度,随着冷却速率的增加,枝晶的生长会偏离择优取角向温度梯度方向偏转,反之主晶间距和抽拉速度增大,枝晶的生长角度逐渐从温度梯度方向朝着晶体择优方向偏转.此外,自适应有限元法相较于均匀网格法在CPU的运行时间上降低了一个数量级,并且随着计算域的增大,自适应有限元法的计算效率越高.     

纳米银枝晶的电沉积及结构表征

采用恒电位电沉积法,选择十二烷基磺酸钠(SDS)为表面活性剂,在Ti基体上制备了具有树枝状结构的纳米银。X-射线衍射试验表明银纳米枝状体为单晶结构,属于面心立方晶系。运用扫描电镜对枝晶的形貌特征进行观察分析,通过高分辨透射电子显微术对枝晶的晶格结构进行表征,发现枝晶表面由{111}晶面组成,主干和分支互成60°分别沿110方向生长,枝晶的{111}晶面形成多次孪晶结构。树枝状晶体形态的产生符合分形生长机理。     

梯温场中玻璃陶瓷定向析晶的过程及工艺

以析晶理论和热传导理论为基础，研究了梯温场中玻璃陶瓷定向析晶的过程和工艺，分析了梯温场主要工艺参数——温度梯度、析晶界面温度、热源升温速率、边界条件等对定向析晶的影响，研究结果对于制定定向析晶工艺，制备性能优良的定向析晶玻璃陶瓷有一定意义。     

强磁场对Al-4.5％Cu合金枝晶生长行为影响的初步研究

以Al-4.5%Cu合金为对象进行了稳恒强磁场对枝晶生长行为影响的初步研究,发现10 T的强磁场明显影响了Al-4.5%Cu枝晶定向生长组织.生长速度R在5,10,20μm/s时,无磁场的条件下形成规则的树枝晶的组织,施加10 T强磁场后,界面淬火枝晶组织变得不规则,在随后的凝固过程中树枝晶组织几乎消失,形成接近胞晶形态的组织.磁场强度达到4 T以上后,枝晶间距明显增加.施加强磁场后宏观组织细化,晶粒增多,形成定向凝固下的等轴晶组织的特殊现象.随着生长速度的增加,磁场的作用逐渐减弱.     

Sn—Pb合金的三次树枝晶生长

在定向凝固的条件下对Ｓｎ－Ｐｂ合金的三次树枝晶生长进行了研究。探讨纵向和横向生长的三次树枝晶形态，给出了三次枝晶间距与工艺参数即温度梯度和生长速度之间的指数衰减关系。发现纵向和横向三次枝晶在枝晶粗化和间距上存在着明显的差别，并探讨了枝晶爬行对枝晶不对称生长的影响。     

定向凝固制备多晶硅柱状晶的研究

为了控制定向凝固过程中柱状晶的稳定生长,结合真空定向凝固技术,在一定的工艺参数下,利用真空定向凝固设备成功制备出具有单向凝固组织的多晶硅材料,通过对制备的多晶硅锭从纵截面和不同位置横截面的微观组织进行研究,分析得出了定向凝固过程中多晶硅垂直于底部的柱状晶和大晶粒形成的最佳工艺参数,通过X射线衍射检测,显示晶体择优取向为<111>面,文章还利用晶粒淘汰机制和柱状晶合并机制合理解释柱状晶体长大过程.     

强磁场对半无限Al/Cu固液扩散偶凝固组织的影响

采用半无限Al/Cu扩散偶法,对磁场下Al-Cu合金凝固组织进行研究.结果表明:由于沿扩散方向Cu原子分数逐渐减小,凝固时,沿凝固方向依次生成α-Al胞/枝状晶等组织、Al-Al2Cu共晶组织和Al2Cu过共晶组织;在不同磁感应强度下(0～12 T),各组织发生了明显变化,胞状晶消失,枝晶粗化并发生偏转;共晶组织层间距与磁感应强度呈非线性关系,组织被扭曲;过共晶组织界面形貌变平整;Cu原子扩散距离缩短.利用XRD对α-Al枝晶区进行衍射分析,发现磁场下α-Al(100)晶面峰值强度变弱,(111)晶面变强.理论分析认为,强磁场对熔体流动的抑制作用和磁场下晶体的磁各向异性是导致上述现象的主要原因...     

电铸Cu的显微组织、晶粒取向和晶界结构

采用SEM,TEM和EBSD研究了电铸Cu的微观组织形貌、晶粒取向和晶界特征.SEM观察表明,沿沉积方向,组织由细小等轴晶区、等轴晶和柱状晶的混合晶区转变为粗大柱状晶区.EBSD分析表明,对于所有晶区,小角度晶界(15°)的分布频率较小,大角度(≥15°)晶界为电铸Cu组织的主要晶界.在大角度晶界中,CSL晶界占有很大比例,其中Σ3的分布频率较大.柱状晶由平行分布的层状孪晶构成,近似垂直于沉积厚度方向,层间孪晶界为Σ3类型,TEM的观察也显示了孪晶的存在.细等轴晶区晶粒的择优取向不明显,混合晶区和粗柱状晶区有明显的〈111〉和〈101〉择优取向.在粗柱状晶区,平行于沉积厚度方向,具有较强的〈111〉择优取向,表明大多数{111}孪晶面垂直于沉积厚度方向.     

Dendrite morphology and evolution mechanism of nickel-based single crystal superalloys grown along the o0014 and o0114 orientations

Nickel-based single crystal superalloys oriented along the o0014 and o0114 lattice directions were produced by a bottom seeding technique in an attempt to understand the evolution mechanism of the dendrite grown along different orientations in the present study. The changes in primary dendrite arm spacing for single crystal with different orientations are also discussed. It was found that the dendrite morphologies of single crystal superalloy grown along o0114 were different from that of o0014. Firstly, the dendrites showed the irregular cruciforms and array in rows in a transverse section. Secondly, no typical primary dendrites were observed but the dendrite morphologies appeared like the letter ‘‘V’’ or ‘‘W’’ in a longitudinal section. The primary dendrite arms grew along the o0014 orientation from the bottom of the sample in the o0014 orientation. However, in the o0114 orientation, the single crystal developed by continuous side-branching along the [001] and [010] orientations. The primary dendrite arm spacing was as the function of the deviation angle f. It indicates that with the increase in the deviation angle f, the primary dendrite arm spacing first increased, and then decreased.     

PAN基炭纤维中石墨微晶的取向度及其与抗拉模量的关系

本文采用单色Ｘ射线透射平板照相法，测定了ＰＡＮ基炭纤维高温热处理后其内部石墨微晶的取向度，讨论了高温热处理条件对取向度的影响，以及取向度与抗拉模量的关系。结果表明：热处理温度越高，取向度愈小，抗拉模量愈高；升温速加快时，取向度增大，说明微晶折择优取向过程需要一定的时间。     

Gradient distribution of radial structure of PAN-based carbonfi ber treated by high temperature

High-performance graphite fibers were prepared and analyzed. The gradient distribution of radial structure of PAN-based carbon fibers was characterized by two different Raman test methods(incident laser beam perpendicular to and parallel to the fiber axis) and studied by the distribution of graphitization degree. Meanwhile difference between the two Raman test methods was used to describe the orientation of the graphite crystallite along the fiber axis. The results showed that the radial structure of PAN-based carbon fiber presented different gradient distribution states at different heat treatment temperatures,and the graphitization degree in the skin region changed more rapidly compared with the core region since the skin region was more affected by temperature which resulted in the obvious difference between skin and core structures.The difference of graphitization degree(Δg) characterized by two different Raman test methods increased with heat treatment temperature,indicating that the high temperature treatment(HTT) promoted further stacking of graphite crystallite,and the orientation degree of the graphite crystallite along the fiber axis was continuously increased.     

双层辉光离子渗金属技术沉积氮化钛薄膜的微观结构研究

采用双层辉光离子渗金属技术,在硬质合金基体表面上制备了氮化钛（TiN）薄膜,通过微观结构和显微硬度分析,研究了基体温度对TiN薄膜性能的影响.实验结果表明：所有TiN样品均具有面心立方结构,并且薄膜生长的择优取向、晶粒尺寸、晶面间距、晶格常数和微观硬度等都与基体温度密切相关.当基体温度为650～780℃时,TiN薄膜具有最小的晶粒尺寸（26.9 nm）和最大的显微硬度（2204 HV）.     

过冷金属熔体中枝晶生长的各向异性效应

基于Karma-Rappel相场模型,模拟了纯金属在量纲为1过冷度为0.45时等轴枝晶生长过程中晶粒形貌和温度场的变化. 研究了不同各向异性条件下等轴晶晶粒形貌的演化过程. 模拟结果显示,各项异性系数的大小对晶粒的形貌有重要影响. 当各项异性为0.05时,枝晶在生长过程中出现了"颈缩"现象,枝晶中温度梯度最大的方向总是与最优生长方向保持一致.     

Natural examples of olivine lattice preferred orientation patterns with a flow-normal a-axis maximum

Tectonic plate motion is thought to cause solid-state plastic flow within the underlying upper mantle and accordingly lead to the development of a lattice preferred orientation of the constituent olivine crystals. The mechanical anisotropy that results from such preferred orientation typically produces a direction of maximum seismic wave velocity parallel to the plate motion direction. This has been explained by the existence of an olivine preferred orientation with an 'a-axis' maximum parallel to the induced mantle flow direction. In subduction zones, however, the olivine a axes have been inferred to be arranged roughly perpendicular to plate motion, which has usually been ascribed to localized complex mantle flow patterns. Recent experimental work suggests an alternative explanation: under conditions of high water activity, a 'B-type' olivine preferred orientation may form, with the a-axis maximum perpendicular to the flow direction. Natural examples of such B-type preferred orientation are, however, almost entirely unknown. Here we document widespread B-type olivine preferred orientation patterns from a subduction-type metamorphic belt in southwest Japan and show that these patterns developed in the presence of water. Our discovery implies that mantle flow above subduction zones may be much simpler than has generally been thought.     

Ni—ZrO2复合镀层中微粒与基质金属间的相互作用（Ⅰ）

利用ＳＥＭ、ＴＥＭ、ＸＲＤ等测试手段，对Ｎｉ－ＺｒＯ２复合镀层的组织结构进行了研究，实验表明，复合镀层中ＺｒＯ２微粒的存在，改变了基质金属Ｎｉ的晶体择优取向和点阵常数，从而证明了复合镀层中基质金属Ｎｉ与ＺｒＯ２微粒之间并不是简单的机械混合，其间存在相互证明。     

取向条件下N-甲基壳聚糖溶液浇铸膜中晶片聚集体的形成

用正交偏光显微镜观察取向了的硼(N-甲基壳聚糖)=30％的N-甲基壳聚糖／甲酸溶液浇铸膜中一种特殊的结晶形态．晶片呈圆形堆砌．其聚集体的直径为几十微米．晶片聚集体内晶片无规取向．但晶片聚集体整体沿剪切方向取向．扫描电镜和X光衍射实验证实了取向浇铸膜中晶片的这种堆砌方式．这种形态是先取向后结晶形成的．