稀土镁球墨可锻铸铁第一阶段石墨化过程石墨并粗的研究

本文对稀土镁球墨可锻铸铁第一阶段石墨化过程石墨并粗现象进行了实验及理论分析。研究表明石墨并粗在石墨化后阶段表现突出，石墨生长平均尺寸的三次方与时间呈线性关系。     

Fe-2.3Si-3.7C合金中渗碳体的石墨化

为了探索白口铁的石墨化机理,研究了Fe-2.3Si-3.7C合金中石墨化形核及长大过程.通过电子显微分析、光学金相分析发现,石墨可以在奥氏体中、渗碳体中、渗碳体/奥氏体的相界面上形核,但在奥氏体中的形核几率最大.石墨化形核速度很快,硅在渗碳体的石墨化过程中起到异乎寻常的促进作用.渗碳体的石墨化是通过渗碳体溶解、熔断,碳原子长程扩散,石墨形核并且不断长大的过程.     

稀土元素对过共晶铸铁中石墨一次结晶的作用及其机理

从过共晶铸铁中石墨形态的考察入手,用液淬和热解石墨生长的方法,研究了稀土元素对过共晶铸铁石墨一次结晶的作用。结果指出,不论初生或共晶石墨都可蠕化,而石墨蠕化是稀土元素作用的结果,奥氏体的作用是次要的。但石墨发生弯曲的主要原因是奥氏体而不是稀土元素。首次提出了光滑界面晶体生长时,螺旋台阶增殖的观点,并给出了两个基本增殖模型,据此解释了石墨结晶形貌问题。     

铸铁中渗碳体高温石墨化研究

为了解决离心球墨铸铁管自由渗碳体墨化问题，研究了白口铁石墨化形核，长大机理，计算了渗碳体石墨化驱动力及恒温转动力学，通常光学金相和电子显微分析发现，石墨可以在奥氏体中，渗碳体及奥氏体与渗碳体的相界面形核，而在奥氏体中形核几率较大，计算结果表明，硅大大地提高了石墨化驱动力，高温石墨化动力学较好地符合Avrami方程。     

关于可锻铸铁预温处理与石墨化关系的研究

本文通过透射电镜和扫描电镜的分析,查明了可锻铸铁的石墨化在预温处理阶段,即在低于临界温度的阶段已开始进行,不像一般文献中所认为的那样需在奥氏体区域内始能进行。在低于临界温度下的石墨化,各种温度都能进行,也就是说对温度而言石墨化的发生是连续的,并非在某一特定温度才突然发生的。所产生的石墨核心(颗粒)以400-550℃最多。低温处理或高温处理对整个退火时间来说没有显著的区别,但低温处理最终获得的石墨颗粒较细小,数目多,形态较为集聚。     

石墨球化机理新探

首次提出“球晶热力学不稳定区”的概念,论证了球化处理的热力学贡献;将结晶学的界面稳定性理论用于解释球状石墨的生长过程,提出石墨球“界面动力学稳定性”的概念,分析了球化处理的动力学贡献;并从界面生长理论出发,论证了石墨球生长的晶格位向条件。     

各种处理剂处理的蠕虫状石墨铸铁的凝固过程

通过对各种处理剂处理的蠕虫状石墨铸铁凝固过程的研究,共晶反应时石墨的析出过程已经明确。从共晶反应冷却曲线可看到两个转变阶段:第一阶段,共晶反应前形成的球状石墨伴随奥氏体壳生长;第二阶段形成蠕虫状石墨,因包围球状石墨的奥氏体部分熔解,使它与熔液接触生长。从而,说明了共晶凝固第一阶段形成的球状石墨为蠕虫状石墨生长的起点。     

稀土镁球墨可锻铸铁第一阶段石墨化动力学研究

本文研究了稀土镁球墨可锻铸铁第一阶段石墨化动力学过程。研究表明石墨生长受碳原子传质过程与渗碳体分解双重因素控制,而渗碳体分解具有更重要的作用,石墨化后期亦完全由渗碳体分解所控制。论文对由界面反应、传质过程、渗碳体分解控制三种情况下的Avrrami方程n值进行了量化。     

可锻铸铁白口组织对石墨化的影响

用扫描电镜和透射电镜观察了 Si-Bi-Al 复合孕育处理的可锻铸铁石墨化退火前的白口铁试样观察结果表明,与用常规孕育处理的试样比较,其组织中珠光体层片排列出现紊乱、重叠、弯折等现象,同时它位错密度显著增加,经热处理试验证实,这种试样在奥氏体转变温度(720℃)以下边疆保温能迅速实现完全石墨化.     

化学成分对球墨可锻铸铁石墨化的影响

本文利用测量石墨化膨胀的方法和OMNICOM图像分析仪,研究了化学成分对球墨可锻铸铁高温和低温石墨化的影响。结果表明,碳对球墨可锻铸铁第一阶段石墨化的影响不同于可锻铸铁,碳量增加有利于第二阶段石墨化;硅对其高温和低温石墨化有显著影响;当Re、Mg残留量小于0.09～0.10％时,第一阶段石墨化时间随其含量提高而降低,但是,Re、Mg超过0.10％后,石墨化时间又提高,Re、Mg量提高阻碍第二阶段石墨化;加入AI、Bi后;其退火石墨数增加,退火时间缩短。     

Grain growth of Al-4Cu-Mg alloy during isothermal heat treatment

The microstructure of an Al-4Cu-Mg alloy during isothermal heat treatment in the Strain Induced Melt Activation （SIMA） process was investigated and the kinetics of grain growth was analyzed, The grain growth during isothermal heat treatment of the Al-4Cu-Mg alloy coincided with the Ostwald ripening theory. During isothermal heat treatment, both grain shape and the high volume fraction of solid phase have significant effects on grain growth. Therefore, a new grain growth model based on the Ostwald ripening theory was proposed taking into consideration the grain shape and the volume fraction of solid phase. By comparing the calculated results with the experimental results, it was confirmed that the present model could be applied to grain growth during isothermal heat treatment of the Al-4Cu-Mg alloy in the SIMA process.     

Microscopic phase-field simulation for coarsening behavior of L12 and DO22 phases of Ni75CrxAl25-x alloy

Based on the microscopic phase-field dynamic model and the microetasticity theory, the coarsening behavior of L12 and DO22 phases in Ni75CrxAl25-x alloy was simulated. The results show that the initial irregular shaped, randomly distributed L12 and DO22 phases are gradually transformed into cuboidal shape with round comer, regularly aligned along directions [100] and [001], and highly preferential selected microstructure is formed during the later stage of precipitation. The elastic field produced by the lattice mismatch between the coherent precipitates and the matrix has a strong influence on the coarsening kinetics, and there is no linear relationship between the cube of the average size of precipitates and the aging time, which does not agree with the results predicted by the classical Lifshitz-Slyozov-Wagner. The coarsening processes of L12 and DO22 phases are retarded in elastically constrained system. In the concurrent system of L12 and DO22 phases, there are two types of coarsening modes: the migration of antiphase domain boundaries and the interphase Ostwald ripening.     

脉冲电场对球墨铸铁第二阶段石墨化中珠光体转变的影响

通过实验研究了脉冲电场对球墨铸铁第二阶段石墨化过程中珠光体转变的的影响。进而分析了脉冲电场作用下基体中石墨晶核的数量增加，有效地缩短了珠光体分解时碳原子的扩散距离，从而加速了第二阶段石墨化过程中珠光体的转变。研究结果表明：脉冲电场加快了第二阶段石墨化过程中珠光体的分解速度，使基体中的铁素体量增加。     

梭形Fe_5(PO_4)_4(OH)_3·2H_2O的一步水热法制备及生长机理研究

采用可控的一步水热法制备出了具有对称棱边的梭形Fe5(PO4)4(OH)3·2H2O产物。利用X-射线衍射、场发射扫描电子显微镜、透射电子显微镜等手段对产物进行了表征,发现产物的生长机理符合Ostwald熟化过程。研究表明:在180℃下反应96h后会得到多臂形貌的纯相Fe5(PO4)4(OH)3·2H2O产物,且在低温下更容易获得纯相的Fe5(PO4)4(OH)3·2H2O梭形产物。此外研究发现,产物在500℃热处理后具有较好的形貌和尺寸上的热稳定性。     

磁性空心纳米粒子的制备及其生物医学应用

总结了近年来磁性空心粒子的制备方法及其制备过程中的优缺点,对磁性空心纳米粒子的特殊形成机理(如柯肯达尔效应和奥斯特瓦尔德熟化机理)进行了说明,并阐述了近年来磁性空心纳米粒子应用于药物运输、磁共振成像等方面的进展,指出当前应用中的主要方向和亟待解决的问题。     

Microscopic phase-field simulation for coarsening behavior of L12 and DO22 phases of Ni75Cr x Al25? x alloy

Based on the microscopic phase-field dynamic model and the microelasticity theory, the coarsening behavior of L1₂ and DO₂₂ phases in Ni₇₅Cr _x Al_25−x alloy was simulated. The results show that the initial irregular shaped, randomly distributed L1₂ and DO₂₂ phases are gradually transformed into cuboidal shape with round corner, regularly aligned along directions [100] and [001], and highly preferential selected microstructure is formed during the later stage of precipitation. The elastic field produced by the lattice mismatch between the coherent precipitates and the matrix has a strong influence on the coarsening kinetics, and there is no linear relationship between the cube of the average size of precipitates and the aging time, which does not agree with the results predicted by the classical Lifshitz-Slyozov-Wagner. The coarsening processes of L1₂ and DO₂₂ phases are retarded in elastically constrained system. In the concurrent system of L1₂ and DO₂₂ phases, there are two types of coarsening modes: the migration of antiphase domain boundaries and the interphase Ostwald ripening. Foundation item: Project(50671084) supported by the National Natural Science Foundation of China; Project(20070420218) supported by China Postdoctoral Science Foundation     

一维棒状氧化铋的控制合成与生长机制

以Bi(NO3)3·5H2O为原料,NaOH为沉淀剂,DESB(十二烷基乙氧基磺基甜菜碱)为控制剂,采用一步水相沉淀法,在温和条件下(70℃)制备了直径约为4μm、长度为几十微米的棒状一维氧化铋.通过X射线衍射(XRD)、扫描电镜(SEM)、能量色散X射线(EDX)对其晶体结构、相组成、微观形貌及可能的生长机制进行了表征和分析.结果表明,所得两端呈尖角的棒状结构为高纯度的单斜相氧化铋,并且具有较好的结晶度.根据实验结果,推测定向附着(oriented attachment)与奥斯特瓦尔德熟化(Ostwald ripening)共同作用为其可能的生长机制.     

One-pot synthesis of hollow octahedral Cu2O nanostructures at room temperature

Homogeneous hollow Cu2O octahedral nanostructures have been fabricated by a facile one-pot reduction reaction at room temperature. The microscope analysis revealed that the edges of as-prepared hollow structures were around 200 nm with a wall thickness of about 20 nm. To investigate the influence factors and formation mechanism of the hollow octahedral structure, samples subjected to different reaction conditions were studies. The results showed that the morphology and structures of Cu2O particles were greatly affected by the concentration of pH value of the reaction environment and the reaction time. Ostwald ripening process is proposed to explain the growth mechanism of the hollow octahedral nanostructures.     

Effects of Extrusion Processing on Microstructure of 7075Al Alloy in the Semi-solid State

A recrystallization and partial melting(RAP) process was introduced to prepare the semi-solid 7075 aluminum alloy used for thixoforming. In order to obtain an ideal semi-solid microstructure, a series of extrusion experiments were conducted to comparatively investigate the optimum extrusion process parameters. Commercial 7075 Al alloy samples were firstly extruded with varying extrusion ratios below the recrystallization temperature followed by homogenization, then these samples were reheated to the semi-solid state and held in the range of 5 to 50 minutes. The experimental results show that varying process cause the difference in the deformation degree and microstructure for as-extruded samples, resulting in various semi-solid microstructure. It is verified that the formation of equiaxed grains in semi-solid microstructure depends on recrystallization behavior of extruded samples during partial melting. Both relative high extrusion temperature and low extrusion ratio lead to high volume fraction of recrystallized area, thus entirely equiaxed solid grains in semi-solid 7075 Al alloy samples can be obtained finally. In addition, Ostwald ripening was determined as the dominate coarsening mechanism of solid grains in semi-solid state for this 7075 Al alloy during the RAP route. The influence of predeformation on recrystallization behavior of this 7075 Al alloy was discussed in detail.     

Computer simulation of strain-induced morphological transformation of coherent precipitates

The coherent elastic strain-induced morphological transformation of a binary cubic model alloy was simulated with different strain energy parameters. The microscopic diffusion equation was combined with the theory of microscopic elasticity. The results show that when the strain energy is neglected, the randomly distributed equiaxed particles are obtained with isotropic characteristic. It is coarsening that follows the Ostwald ripening mechanism: smaller particles dwindle and larger particles grow; when the elastic strain is considered, plate precipitates tend to align along the elastically soft directions <01> with anisotropic characteristic. The par-