碳纳米带的结构与生长机制研究

采用热化学气相沉积技术在单晶硅衬底上制备了碳纳米带,并采用场发射SEM、TEM、激Raman光谱等分析手段对其形态和结构进行了研究.实验采用乙炔(C2H2)为碳源,铁为催化剂,获得了厚度在几十纳米、宽度在几百纳米,长度在100 μm量级的碳纳米带.研究发现:碳纳米带是一种准二维材料,其碳层沿着与其生长轴方向一致的(002)晶向向的排列,碳层的边缘都弯曲折叠成封闭结构.碳层的排列不很平直,其中存在大量的层错.对碳纳米带的生长机制的研究表明:碳纳米带的生长是通过碳原子从片层状催化剂侧面的扩散、析出来实现的.     

SnAgCuCe/Er无铅钎料表面锡晶须的形态及特性

在Sn-3.8Ag-0.7Cu无铅钎料中添加1%(质量分数)的稀土铈或铒会在其内部形成尺寸较大的稀土相CeSn3和ErSn3.暴露于空气中的CeSn<,3和ErSn3将发生氧化,同时在其表面会出现锡晶须的快速生长现象.文中研究了稀土相CeSn3与ErSn3表面锡晶须的生长行为.结果表明,在CeSn3与ErSn3表面形成了大量的传统圆柱状锡晶须,同时,在其表面还出现了一些特殊形态的锡晶须,如带纹状的锡晶须、扭曲状的锡晶须、变截面的锡晶须、锡晶须的分枝、合并及搭接现象等.     

四针状氧化锌晶须的生长机理

用"时间标尺"实验法测定了T-ZnO晶须在不同生长时期的生长速率,用扫描电镜观察分析了不同条件下晶须的生长形貌.结果表明:T-ZnO晶须的结晶作用是气-液-固(VLS)方式,晶须生长受螺旋生长机理控制;锌蒸气中产生凝聚生长的锌液滴是制备T-ZnO晶须的关键,锌从液滴内向外扩散在晶须的端面产生生长台阶,随着液滴内的原子向外不断扩散,针体部分就不断地伸长生长,当液滴内的原子全部消耗尽时,晶须便不再发生轴向生长;气-固(VS)方式的作用主要是促进晶须棱面生长而使晶须变粗,对轴向生长几乎没有影响.     

Fatigue crack growth mechanism in cast hybrid metal matrix composite reinforced with SiC particles and Al2O3 whiskers

The fatigue crack growth (FCG) mechanism of a cast hybrid metal matrix composite (MMC) reinforced with SiC particles and Al₂O₃ whiskers was investigated. For comparison, the FCG mechanisms of a cast MMC with Al₂O₃ whiskers and a cast Al alloy were also investigated. The results show that the FCG mechanism is observed in the near-threshold and stable-crack-growth regions. The hybrid MMC shows a higher threshold stress intensity factor range, ΔK_th, than the MMC with Al₂O₃ and Al alloy, indicating better resistance to crack growth in a lower stress intensity factor range, ΔK. In the near-threshold region with decreasing ΔK, the two composite materials exhibit similar FCG mechanism that is dominated by debonding of the reinforcement–matrix interface, and followed by void nucleation and coalescence in the Al matrix. At higher ΔK in the stable- or mid-crack-growth region, in addition to the debonding of the particle–matrix and whisker–matrix interface caused by cycle-by-cycle crack growth at the interface, the FCG is affected predominantly by striation formation in the Al matrix. Moreover, void nucleation and coalescence in the Al matrix and transgranular fracture of SiC particles and Al₂O₃ whiskers at high ΔK are also observed as the local unstable fracture mechanisms. However, the FCG of the monolithic Al alloy is dominated by void nucleation and coalescence at lower ΔK, whereas the FCG at higher ΔK is controlled mainly by striation formation in the Al grains, and followed by void nucleation and coalescence in the Si clusters.     

反应合成Ni-Al金属间化合物的组织及形成机理(英文)

以Ni粉和Al粉为原料,通过热爆反应合成制备Ni-Al系金属间化合物,研究了反应物摩尔比对生成物物相、组织结构和显微硬度的影响。结果表明:当Ni、Al摩尔比为1:1时,反应生成物为单一的NiAl相;当Ni、Al摩尔比为2:1时,生成物相组成为NiAl+Ni3Al相,因为非平衡冷却,NiAl含量多,呈不规则块状形态分布,Ni3Al相析出量少,主要沿初生NiAl晶界分布,当进一步提高Ni含量,且Ni、Al摩尔比为3:1时,生成物组织形态复杂,除枝晶状的β-NiAl、粗大块状和网状的γ-Ni3Al外,还有板条状和针片状的M-NiAl和不规则的块状或者尖条状的γ′-Ni3Al,这主要是由非平衡冷却和β-NiAl内的成分差异而引起的。     

电迁移诱发镀层锡须生长行为分析

分析了0.3×104 A/cm2恒定电流密度和四种不同加载时间（0,48,144和240 h）电迁移条件对6.5 μm厚镀锡层表面锡须生长行为的影响,以及不同电流密度对阴极裂纹宽度的影响.结果表明,电迁移加速了镀层表面锡须的形成与生长,随着电迁移时间的延长,锡须长度不断增加.此外,电迁移导致在阴极首先出现了圆形空洞,随后在两极均形成了圆形空洞,并且在阴极处还发现有微裂纹存在,随着电流密度增加,阴极裂纹宽度也随之增加,电流密度为0.5×104 A/cm2时,平均最大裂纹宽度约为9.2 μm.     

Microstructure and stopped growth mechanism of Y123 bulk fabricated by directional infiltration and growth

The infiltration-growth process was used as an alternative to conventional melt processing techniques for the preparation of bulk YBa2Cu3O7-x(Y123) with freely dispersed small size Y2BaCuO5(Y211) particles. Bulk YBCO superconductors with uniformly distributed particles of micron-sized Y211 were prepared by the directional infiltration and growth(DIG). The microstructure changes of the Y211 particles at various stages of processing were studied. About 70% of Y211 particles are under 1μn in the final sample. The different stopped growth mechanism of this material along the c axis and ab plane was discussed.Undercooling and viscosity lead to tanglesome thick boundary layer. So the Y123 growth along c axis is stopped. Yttrium lack in front of the ab plane is the main reason why the growth stops at this direction.     

Microstructure and strengthening mechanism of Ni3Al intermetallic compound

Structural studies have been performed on precipitation hardening found in Ni₃Al-base ordered alloys using transmission electron microscopy. The γ′ phase hardens appreciably by the fine precipitation of disordered γ. The strength of γ′ increases over the temperature range of experiment by the precipitation of fine γ particles. The peak temperature where a maximum strength was obtained shifted to higher temperature. Superlattice dislocations dissociate into fourfold Shockley partial dislocations in a uniform supersaturated solid solution of the γ′ phase. Dislocations are attracted into the disordered γ phase and dissociate further in the particles. At any stage of aging, dislocations cut through the particles and the Orowan bypassing process does not occur even in the overaged stage of this alloy system. When the applied stress is removed, the dislocations make cross slip into (010) plane, while those in γ precipitates remain on the (111) primary slip plane. The increase of high temperature strength in γ′ containing γ precipitates is due to the restraint of cross slip of dislocations from (111) to (010) by the dispersion of disordered γ particles. The orientation dependence of strength is decreased by the fine precipitation of a disordered γ phase.     

Sn-Zn-Ga-Pr钎料表面锡须的自发生长

结合扫描电镜与电子能谱分析了稀土元素对无铅钎料显微组织的影响.结果表明,当无铅钎料中的稀土添加过量,会诱发锡须在无铅合金表面的自发生长.在向Sn-9Zn-0.5Ga基体合金中添加0.7%(质量分数)的稀土元素镨(Pr)后,仅需室温时效12 h,合金组织中的稀土相表面即发生了锡须的自发生长.随着时效时间的延长,锡须会继续长大,其最终长度可达100μm.最后对过量稀土元素添加导致锡须生长的力学原因作了初步探讨,分析认为稀土相氧化所产生的微观压应力可能为锡须的生长提供了驱动力.     

外加载荷对镀锡层锡须生长行为的影响

首先研究了三种不同厚度镀锡层（3,5,13 μm）在相同试验条件（70℃时效24 h后室温放置60天）下的锡须生长情况,并在此基础上首次采用精密动态力学分析仪（DMA Q800）研究了精确控制相同载荷条件下拉、压两种外力对相同厚度镀锡层（3 μm）锡须生长行为的影响.结果表明,相同时效条件下,镀锡层越薄,锡须生长的可能性越大;相同的外加载荷和试验温度作用下,承受压力作用镀锡层,其表面锡须生长比承受拉力时生长更快,并且主要呈柱状生长.     

Microstructure variation and growth mechanism of hypoeutectic Al-Si alloy solidified under high pressure

The microstructure of hypoeutectic Al-9.21wt.%Si alloy solidified under 5.5 GPa was studied. The results show that the solidification microstructure is refined. The primary a phase is the extended solid solution.The solid solubility of Si in a phase is up to 8.26wt.%. The growth mode of the a phase is cellular, and this cellular growth mechanism is interpreted in terms of the decrease of the diffusivity and the extended solid solution under high pressure. By calculation, it can be known that the the diffusivity of solute in the liquid under normal pressure is as high as two hundred times that under high pressure. The microhardness of the hypoeutectic Al-Si alloy solidified under high pressure is higher than that of solidified under normal pressure. After annealing, Si precipitates from the solid solution, the microhardness of the alloy decrease, but, still higher than that of solidified under normal pressure.     

碱式氯化镁晶须的水热制备及热分解机理研究

采用水热法以氯化镁溶液、氢氧化钠为原料制备了碱式氯化镁晶须。通过SEM和SAED观察样品的显微形貌及晶体结构,晶须长度150μm以上,直径0.5~1μm,为单晶物质。通过XRD测定样品的晶相结构,产物为碱式氯化镁9Mg(OH)_2·MgCl_2·5H_2O。通过红外光谱考察了不同镁离子浓度产物官能团的不同。升温速率为2~5℃/min,高温程序煅烧前驱体碱式氯化镁,制备出氧化镁晶须,很好的保持了碱式氯化镁晶须的形貌,仍为单晶物质,并推测了其可能的热分解的机理过程。     

碳热还原合成Ti(C,N)晶须的相转变行为及生长机理

以TiO2和碳黑为主要原料,NaCl为卤化剂,NiCl2作为晶须生长的添加剂,在N2气氛下采用碳热还原法,在不同温度下合成Ti（C,N）晶须。采用X射线衍射研究合成样品的相组成及合成过程中原料的相转变行为,采用扫描电镜观察合成样品的形貌,探讨晶须的生长机理并建立生长模型。结果表明：在1 200℃合成时,主要发生TiO2与碳黑、氮气之间的直接还原反应,形成TiN;在温度为1 250-1 400℃时,NaCl分解产生的Cl原子起卤化作用,从NiCl2中分解出的Ni起催化作用,合成出Ti（C,N）晶须,晶须长度在10-30μm之间,直径大约1μm;合成的晶须表面光滑,顶端残留有催化剂颗粒,具有典型的气-液-固晶须生长机制特征。     

微/纳米氧化钨晶须的制备工艺及原理

采用溶胶-水热反应法，通过添加适量的硫化钠结晶体诱导制备了微／纳米氧化钨晶须。利用扫描电镜观察氧化钨样品的形貌特征，并对氧化钨晶须进行能谱测试，用X射线衍射仪对氧化钨样品进行物相分析和晶面测定，用透射电镜观察微／纳米氧化钨晶须／线的生长特征。结果表明：未添加硫酸钠时，在180℃水热反应12～36h只能得到氧化钨颗粒粉末，而添加适量硫化钠后，可制备出直径为0．2～0．3μm、长径比为5～50的氧化钨晶须和直径为10～30nm、长径比为50～200的氧化钨纳米线；氧化钨纳米线晶体结构良好，物相为六方晶系WO3；微／纳米氧化钨晶须／线主要沿〈200〉，〈002〉，〈202〉和〈100〉方向定向生长。     

锡晶须生长机理研究的现状与问题

介绍锡晶须的发现过程以及机制研究和预防策略,总结锡晶须生长过程中已经被一些研究人员发现的特点,如晶须形貌的多样性、生长过程的阶段性以及生长位置的不确定性等。回顾从最初发现锡晶须到现在所提出的用于解释锡晶须生长机理的理论模型,其中主要是位错机制、压应力机制、再结晶机制、氧化膜破裂机制以及活性锡原子机制。在对于这些理论模型的问题进行评述后,对如何进一步探索晶须的生长机理提出一些看法。     

Si_3N_4复合陶瓷材料的微观组织和断裂机制

使用AEM和HREM研究了添加纳米SiC颗粒和同时添加纳米SiC颗粒及SiC晶须的两种Si3N4 复合陶瓷材料的微观组织和断裂机制。结果表明 ,部分SiC颗粒分布在Si3N4 晶内 ,SiC晶须分布在Si3N4 晶粒之间 ,SiC颗粒和晶须与Si3N4 界面之间不存在第二相组织 ,非晶组织大多分布在Si3N4 三叉晶界。断裂裂纹主要沿晶界和相界面扩展 ,也可能穿过少数Si3N4 晶粒。当裂纹扩展遇到SiC颗粒和 /或SiC晶须时 ,会发生转弯 ,产生分枝裂纹或微裂纹并在Si3N4 晶内和Si3N4 晶粒的断裂表面引起晶格畸变 ,这降低了裂纹扩展能量 ,从而改善复合陶瓷材料的断裂强度和断裂韧性     

新型铸造锡青铜合金的微观组织和性能

利用真空熔炼离心工艺浇铸了ZCuSn10Zn2FeCo合金试样棒。利用SEM、TEM分析了新型铸造合金的微观组织。结果表明：和ZCuSn10Zn2合金相比,ZCuSn10Zn2FeCo合金的抗拉强度提高到了400～450 MPa,提高了70%～90%,伸长率保持在12%以上,没有明显下降。透射电镜下,铜基体中弥散分布着数量众多的细小析出相,直径在2～20 nm之间不等,直径大于100 nm的纳米析出相数量很少。纳米尺寸的析出相对位错的钉轧和阻碍作用明显,位错塞积可见。孪晶组织中存在着高密度的位错和数量众多的纳米析出相,是合金强度提高的重要原因之一。合金的断裂形式呈韧性断裂。