共查询到17条相似文献,搜索用时 171 毫秒
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提出了一种改进元胞自动机方法,该法充分考虑了溶质场和热扩散对枝晶生长的作用,并基于溶质场方程的27点离散格式,对多元高温合金凝固时的枝晶生长行为进行了数值模拟和试验对比,研究了枝晶生长形貌演变和单晶叶片铸件杂晶形成规律。结果表明:增大过冷度能促进枝晶快速生长,但由于溶质富集,单晶粒枝晶尖端生长速率随时间延长而逐渐减小;当冷却速率较低时,铸件等截面区域偏离热流取向的枝晶会淘汰与热流取向相同的枝晶;在定向凝固枝晶生长中,等温线内凹温度场中的变截面区域易形成杂晶;上述模拟计算结果和试验结果及相关文献的研究结果一致,该改进元胞自动机方法具有一定的有效性和实用性。 相似文献
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弱电解质溶液中利用电沉积补偿电极损耗的电火花/电化学复合加工技术可以大幅降低电极损耗,对提高微细电火花加工效率具有重要意义。由于该工艺方法是EDM/ECM复合加工领域一个新的研究方向,研究成果很少。为加深对利用电沉积补偿电极损耗的电火花/电化学复合加工技术的认识,基于实验结果,对弱电解质溶液中的电火花/电化学复合加工的材料去除机理、放电通道形成机理及电极损耗机理进行了初步探索,得到了以下结果:电火花放电蚀除和电化学溶解共同将工件材料去除;大量气泡存在于电极间隙使复合加工放电通道的形成异于电火花放电加工;电沉积作用和电火花放电蚀除共同对工具电极损耗产生影响。 相似文献
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复合电沉积初始阶段预吸附的惰性颗粒对金属离子沉积的影响研究 总被引:1,自引:0,他引:1
研究了复合电沉积初始阶段预吸附的TiO2颗粒对金属镍离子电沉积的影响,首次观察到在复合电沉积初始阶段预吸附的TiO2颗粒导致镍离子异常成核和快速生长的现象.提出了逐步电沉积方法,结合循环伏安曲线和电化学阻抗谱等电化学方法,研究了预吸附TiO2颗粒对镍离子沉积的影响作用.结果表明预吸附的TiO2颗粒能够增加阴极表面的活性位点密度,并减小阴极表面的电荷转移阻抗,从而加快吸附原子的电结晶步骤.结合上述研究建立了预吸附惰性颗粒影响金属离子沉积的物理模型.本研究提供了一种金属离子快速沉积和纵向生长的可能,对于揭示复合电沉积过程中惰性颗粒与金属离子的共沉积机理和行为具有重要意义. 相似文献
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晶粒生长的数值模拟是研究复杂微观组织演变的重要手段,现有的研究较少涉及电弧增材成形中晶粒生长的数值模拟。采用有限元和元胞自动机方法建立了碳钢电弧增材成形过程的宏观传热和微观组织演变的耦合模型,模拟单道第两层熔积的熔池凝固过程中晶粒动态演变过程。模拟结果显示,单道第一层熔积熔池凝固过程中晶粒从熔合线位置形核后向熔池中心生长,在温度梯度方向与枝晶臂优先生长方向的共同作用下,枝晶呈现竞争生长,晶粒优先生长方向与温度梯度方向一致的晶粒生长更快,部分晶粒生长被抑制,最终形成交错、完全粗大的柱状晶组织,枝晶之间出现溶质富集的现象;单道第二层熔积的晶粒在上一层粗大柱状晶基础上形核并生长,随后的生长过程与第一层类似,第二层熔积时熔池温度梯度方向的改变导致晶粒的主要生长方向与第一层之间有一定夹角。与模拟相同成形工艺的成形试样金相照片验证了模拟结果。研究结果可为电弧增材成形微观组织控制以及后续工艺规划提供依据和参考。 相似文献
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基于Sola算法强迫层流纯物质枝晶生长相场法模拟 总被引:2,自引:0,他引:2
采用SIMPLE算法耦合流场的相场法模拟过冷熔体枝晶生长过程计算效率较低.将计算效率较高的自适应压力迭代法修正的Sola算法与相场模型结合,建立模拟过冷熔体在强迫层流状态下枝晶生长的Sola-相场模型(Sola-phase field model, S-PFM),实现过冷熔体流动场与相场的完全耦合,基于该模型模拟高纯丁二腈(SCN)过冷熔体枝晶生长行为.结果表明,过冷熔体在层流状态下,迎流方向枝晶尖端生长速度大于无流动时候的枝晶尖端生长速度,而下游枝晶尖端生长速度小于无流动时候的枝晶尖端生长速度,它与TONG等采用结合SIMPLE算法的相场模型模拟结果一致;并且,流动法向枝晶尖端在其逆流侧出现漩涡初期生长速度不稳定;同时,过冷熔体层流速度越大,迎流方向枝晶尖端生长速度越大,固相率也越高. 相似文献
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以稀土LaCl3作为添加剂,通过极化曲线、微分电容测定,探讨了稀土LaCl3对电铸镍铸液性能的影响及其在电极表面的作用机理,并采用SEM、XRD等现代分析手段对镍电铸层微观结构进行测试。试验结果表明:LaCl3能够在阴极表面发生特性吸附,增大阴极极化,细化精密电铸层晶粒,提高精密电铸的沉积速度,电铸层的显微硬度得到显著提高。 相似文献
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E. BOEHM-COURJAULT‡ F. GONZALES‡ A. JACOT‡ F. KOHLER‡ A. MARIAUX‡ C. NIEDERBERGER‡† M.A. SALGADO-ORDORICA‡ & M. RAPPAZ‡ 《Journal of microscopy》2009,233(1):160-169
This paper presents a few examples of the application of electron back-scatter diffraction (EBSD) to solidification problems. For directionally solidified Al–Zn samples, this technique could reveal the change in dendrite growth directions from <100> to <110> as the composition of zinc increases from 5 to 90 wt%. The corresponding texture evolution and grain selection mechanisms were also examined. Twinned dendrites that form under certain solidification conditions in Al–X specimens (with X = Zn, Mg, Ni, Cu) were clearly identified as <110> dendrite trunks split in their centre by a (111) twin plane. In Zn–0.2 wt% Al hot-dip galvanized coatings on steel sheets, EBSD clearly revealed the preferential basal orientation distribution of the nuclei as well as the reinforcement of this distribution by the faster growth of <10 1 0> dendrites. Moreover, in Al–Zn–Si coatings, misorientations as large as 10° mm−1 have been measured within individual grains. Finally, the complex band and lamellae microstructures that form in the Cu–Sn peritectic system at low growth rate could be shown to constitute a continuous network initiated from a single nucleus. EBSD also showed that the α and β phases had a Kurdjumov–Sachs crystallographic relationship. 相似文献
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G. V. Strukov G. K. Strukova E. D. Shoo S. I. Bozhko Yu. P. Kabanov 《Instruments and Experimental Techniques》2009,52(5):727-730
An automated PC-controlled electrochemical setup for deposition of a specified number of different metal nanodimensional layers
onto conducting substrates is described. Metallic layers are deposited in galvanic cells from solutions of corresponding electrolytes
on a sample that serves as a cathode, while the anode is a plate of an inert material or a material dissolved during electrolysis.
The electroplating is conducted by passing rectangular current pulses through the electrolyte solution between the sample
and the anode. The amplitude (1 mA–1 A) and duration (1 ms–1 s) of the current pulses are set by a program. Samples are treated
in the galvanic cells and rinsing baths according to a programmed route. In combination with efficient electrolytes for electrodeposition,
the setup enables one to obtain multilayer structures of specified configuration with alternation of nanometer layers of different
metals: normal metals, ferromagnets, paramagnetics, antiferromagnets, or superconductors. The characteristics of a normal
metal (copper)-ferromagnet (palladium-nickel alloy) multilayer coating are presented. 相似文献
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Donglin Li Di Zhu Hansong Li 《The International Journal of Advanced Manufacturing Technology》2011,55(1-4):189-194
Electrochemical micromachining (EMM) has been gaining popularity as an alternative method to fabricate microstructure. A method of EMM is proposed to produce microhole array or micro-dimple array, in which a patterned inert metal mask (platinum plate) is closely attached to workpiece (anode), not bonded to the anode. When voltage is applied across the anode and the cathode over which electrolyte flows at a high speed, the patterns in the mask are transferred to the anode, and microstructures are produced. A mathematical model to describe the actual machining process is established. By considering the effect of nonlinear electrolyte, the parametric finite element method is adopted to simulate and numerically analyze the erosion process. Some experiments are performed to verify the proposed model. 相似文献
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Atomic force microscope (AFM) tip-induced nucleation, and dendrite growth of vapor deposited PETN films on Si (100) have been investigated at room temperature. The AFM tip induces a change from smooth and flat morphology to islands and dendrites, which is owing to the lowering and vanishing of 2-D nucleation barrier at the tip contact area; this action gives rise to the formation of large islands in the scanned area and dendrite growth along the scanning boundary. 相似文献