低氢含量工业纯钛循环变形的微观结构Ⅰ.γ氢化物附近的晶体旋转及胞结构的形成

对均匀弥散分布着γ氢化物的低氢含量的工业纯钛进行循环疲劳试验．发现在氢化物碎化之前，位错可以穿过氢化物和基体的共格界面，从而使氢化物发生剪切变形，然而在氢化物碎化之后，位错则不能继续穿过界面，而是在界面处缠结．这被归结于由于氢化物尺寸发生变化导致氢化物内部应力降低，氢化物不能继续发生剪切变形所致．透射电镜观察表明，在氢化物的内部至少能激发3套滑移系统．为了协调氢化物和基体之间的不均匀变形，在氢化物和基体内部都发生了晶体旋转，并且氢化物和基体之间的取向关系遭到了破坏．对相应的晶体旋转的机制进行了讨论．     

氢化物对N18锆合金原位拉伸变形的影响

采用扫描电镜下原位拉伸方法,观察研究了电解渗氢后的N18锆合金中氢化物的变形过程和基体的滑移行为,分析了氢化物对拉伸性能的影响。研究发现,锆合金基体的塑性变形是由多滑移引起的,氢化物可随基体发生较大变形。稀疏分布的带状氢化物簇对滑移的阻碍小,滑移线能够穿过而不改变方向,但尺寸较大的氢化物簇会阻碍滑移带的穿过而改变滑移方向。氢化物使抗拉强度略有增加,伸长率显著下降,但氢含量达到623μg/g的N18锆合金的伸长率仍然达到了13.1%,具有较好的塑性。     

新型绿色电池——金属氢化物／镍电池

金属氢化物—镍电池是一种近年来得到迅速发展的高新技术产品。 与用途最广泛的镉—镍电池相比,金属氢化物—镍电池具有比能量高、无记忆效应、不污染环境、耐过充过放电等优良性能,故被誉为绿色电池。 金属氢化物—镍电池是以贮氢金属材料M作为一个电极,以氢氧化亚镍作为另一个电极,通常采用氢氧化钾水溶液作电解液的一种碱性可充电电池。在充电时,以M作阴极,此时,阴极表面由于水的电化学还原,生成吸附氢原子。吸附氢原子扩散进入阴极,并与贮氢金属材料反应,生成金属氢化物MH_x。在放电时,金属氢化物能释放出所吸收的氢原子,并使其氧化成水,电极反应可表示为:     

铝氢化物合成新工艺

日本原子能研发机构新近开发成功铝氢化物的一种合成新工艺，这种铝氢化物有可能成为新一代贮氢材料。一般在室温下吸收氢气要在1万个大气压的高压下进行，而且由于在铝表面形成氧化膜会妨碍吸氢反应，以致很难通过与氢气的直接反应来合成铝氢化物。然而新的合成法是氢气与铝的直接反应，     

金属氢化物在生产钕铁硼磁体掺合粉末中的应用

在微细粉末生产中广泛地采用了氢气,而在生产磁体时则使用了钕、镝、钒和铌,它们对氢的亲合力很高,并且导致产生脆化效应。与纯金属相比,金属氢化物有以下优点：第一,氢化时的晶格扩大使整体合金碎裂;第二,氢化物脆,易研磨;第三,稀土二氢化物粉末更稳定;第四,粉末吸氢后变得活泼,导致原位合金化;第五,氢的存在提高了固态扩散能力． 事实表明,在钦铁硼磁体生产中添加镝,不仅能够提高基体 Ｎｄ２Ｆｅ１４Ｂ（）的各向异性系数,而且可以增加商品磁体的矫顽磁力,尤其是在高温条件下．典型的稀土添加总量约为１０ａｔ％,这样…     

循环形变下纯钛中两种γ氢化物的不同变形行为

在含氢量（质量分数）为0.0077%的工业纯钛中，观察了两种具有同样结构的γ氢化物的变形行为。利用扫描电镜（SEM）和透射电镜（TEM）对循环载荷下滑移、孪生对两种γ氢化物的相互作用进行了观察。发现在循环形变I型氢化物能够通过滑移机制发生塑性变形，甚至完全碎化，而不会形成孔洞。而Ⅱ型氢化物则难以发生塑性变形。分析了氢化物塑性变形的晶体学机制。     

Zr-4合金中氢化物析出长大的透射电镜原位研究

用透射电子显微镜拉伸试样台原位研究了应力、电子束辐照以及第二相对Zr-4合金中氢化物析出和长大的影响。结果表明,在拉应力作用下,裂纹易于沿氢化物扩展,并在裂尖垂直于拉应力方向析出新的氢化物。氢化物在拉应力诱发下的析出、开裂、再析出·····过程,导致了氢致延迟开裂。在较强的会聚电子束辐照下,Zr-4合金中的氢化物会分解,新的氢化物会围绕着附近的Zr(Fe,Cr)2第二相粒子析出,新析出的氢化物为面心立方结构的δ相。     

单晶硅裂纹尖端的位错发射行为

利用透射电镜原位观察了单晶硅压痕裂纹尖端位错及位错偶沿滑移面的发射行为,考察了滑移面取向,外荷对发射位错及塑性区的影响,结果表明：在I型载荷作用下,滑移面与裂纹面夹角要影响从裂纹尖端发射的位错数量及塑性区,发射出的位错可沿最大切应力方向改变运动方向或交换滑移面运动,实验观察的位错宽度平均值为22．0nm,与Peierls位移框架模型计算的23．6nm相近。     

Cu单晶体驻留滑移带的形成与消失

在循环加载条件下，单滑移取向的Cu单晶体首先出现驻留滑移线(PSL)，然后随着循环周次的增加转变为驻留滑移带(PSB)．在不同温度、不同时间条件下对疲劳Cu单晶进行真空退火处理，观察PSB结构在热激活条件下的变化情况．结果表明，退火处理过程中由于空位浓度差异所产生的渗透力促使位错运动，并使PSB的某些部位逐步细化，以至消失．实现了PSB的分段相消．在退火过程中由于应变能的逐步释放，未观察到再结晶现象．     

氢致Fe-3％Si沿晶界解理断裂

沿晶断裂是氢致开裂的一个重要方式.有人在氢致沿晶断口上观察到大量塑性变形,因而认为氢促进沿晶断裂是氢促进局部塑性变形的结果.但也有人认为是由于氢降低了晶界原子问的结合力造成的。用高压电镜进行动态观察的结果表明,Fe 和 Ni 中氢致沿晶界断裂实际上是由于晶界附近高度塑性变形引起的沿晶界附近的滑移面开裂.我们的工作表明,氢能够促进位错的增殖和运动.对于 Fe-3%Si 单晶体,氢能够促进由于位错运动和反应引起的沿{001}面解理。     

Effect of Hydride and Hydrogen—Induced Martensite on Fracture Toughness of TiNi Alloy

TiNi形状记忆合金在充氢时形成的氢致马氏体和氢化物可使合金的KIC明显下降，相对损失高达96％，但其氢致马氏体对KIC相对损失的贡献仅约1．8％，而且不随氢浓度而改变．因此氢致KIC下降几乎全部归因于氢化物．氢化物引起的相对损失ΔKIC^TiNiH／KIC和氢化物的含量(质量分数，%)WTiNiH有关，即ΔKIC^TiNiH/KIC(％)=93(1-eWTiNiH/9.5)．当充氢电流i≥15mA／cm^2时，在氢化物处能产生微裂纹，但微裂纹不会使断裂韧性进一步下降．     

高氢量氢化的Ti—6Al—4V合金中氢化物的组织结构研究

研究了含氢最为0.16,0.58,0.87,1.49wt—%的Ti—6Al—4V—H合金中出现的各种氢化物,结果表明:氢超过0.58%时,合金中已有Ti_3Al相析出,同时,随着氢含量的增加,氢化物的形态逐渐由低氢的粗板条变到高氢的窄板条,后者组织明显细化,在含氢1.49%的试样中,还观察到四方点阵的氢化物和块状氢化物,并发现孪晶氢化物,根据孪晶氢化物的电子衍射花样的特点,可以简便地判别氢化物为立方或四方结构。     

STRUCTURE OF HYDRIDES IN HIGHLY HYDROGENATED Ti-6Al-4V ALLOY

The microstrueture and various hydrides precipitated in Ti-6A1-4V alloys containinghydrogen 0.16,0.58,0.87,1.49 wt-%,respectively,have been studied by means of TEM andX-ray diffraction.The Ti_3Al phase may precipitate when H over 0.58 wt-%.In the sametime,the morphology of hydrides gradually changed from rugged sheets to narrow laths asH contents increased.The microstructure of highly H-doped alloys is obviously fine.A mas-sive hydride and the hydride with tetragonal lattice were observed in the specimen containing1.49 wt-%H.The twin hydrides were found in the alloys with different H contents and theelectron diffraction patterns of the twin hydrides can be served as a simple criterion for distin-guishing the cubic and tetragonal structures.     

Elastic fields generated by a semi-spherical hydride particle on a free surface of a metal and their effect on its growth

The formation of a metal hydride is associated with a large increase of volume relative to the parent metal and therefore in large strain energies. Effects of elastic energy on the hydriding of metals are revealed in the microstructural evolution and kinetics of hydride growth on free surfaces. In the present work, we study in detail the elastic fields set up by a semi-spherical hydride particle growing at a free surface of metal with cubic symmetry, with and without an oxide layer. These systems combine geometric (structural) and material anisotropies.Three stages along the microstructural evolution on the surface of some hydride forming metals exposed to hydrogen at constant pressure were described experimentally. For these stages along hydride growth, correlations with the elastic fields are suggested as follows. (a) A hydride particle at the free surface generates regions of tensile and compressive hydrostatic stress in the surrounding matrix. This may induce a preferred nucleation of new hydrides and formation of clusters of hydrides precipitates, which is indeed observed experimentally. (b) Clustering, on the other hand, may contribute to the cease of growth due to competition on hydrogen. In addition, as the particle grows, changes in the stress fields may retard further diffusion from the surface and be another contribution to the cease of growth. (c) A growing hydride increases the stress in the oxide layer and may finely break it. Then the elastic energy per unit volume drops to its minimum value and the growth may accelerate. The formation of such “growth center” is favored for that hydride precipitate that grow alone and not in a cluster.     

Exploring Plastic Deformation Mechanism of Multilayered Cu/Ti Composites by Using Molecular Dynamics ModelingEI北大核心CSCD

Multilayered metallic composites have attracted great interest because of their excellent characteristics. In recent years, the mechanical behavior of Cu/Ti composites is described in terms of macroscopic or mesoscopic scales, but the micromechanism regarding dislocation slip, twinning and shear banding at heterogeneous interfaces remains unclear. In this work, the molecular dynamics method is used to study the uniaxial tensile and plane strain compression deformation of the Cu/Ti multilayered composites with characteristic initial crystal orientations. The simulation results show that under the tensile load, dislocations are preferentially nucleated at the heterogeneous interface between Cu and Ti, and then slip along {111} plane within the Cu layers. The corresponding mechanism is confined layer slip. With the multiplication of dislocations, dislocations interact with each other, and intrinsic stacking faults and deformation twins are formed in Cu layers. However, no dislocation slip or twinning is activated within the Ti layers at this stage of deformation. As the load increases, the stress concentration at the Cu/Ti interface leads to the fracture of the composites. For the composites under plane strain compression, the stress concentration at the Cu/Ti interface triggers the formation of shear bands in the Ti layer, and there are only very limited dislocations within the shear bands and their adjacent area. With the increase of applied strain, the common action of various deformation mechanisms causes the grains to rotate, and the disorder degree of complex atoms increases. In addition, the micro-plastic deformation mechanism and mechanical properties of Cu/Ti complex with different initial orientations and strain rates are significantly different. The results reveal the microscopic deformation mechanism of the laminated composites containing hcp metals.     

N18锆合金氢致裂纹延迟开裂临界温度研究

研究了N18锆合金(Zr-1Sn-0.3Nb-0.3Fe-0.1Cr)发生氢致延迟开裂(DHC)临界最大开裂温度(Tc)和临界最小止裂温度(Th)随氢含量的变化规律;同时对裂纹尖端偏聚氢含量及静水应力和发生DHC的临界氢含量进行了理论分析,建立理论模型对临界温度进行理论计算.结果表明:N18合金发生氢致延迟开裂的临界温度介于相同氢含量下溶解固溶温度与析出固溶温度之间,且最大开裂温度小于最小止裂温度,计算的临界温度值与实验值相当吻合,因此该理论模型能够真实反映N18锆合金的氢致延迟开裂的物理过程.     

钛催化氢化铝钠的贮氢性能

通过加入钛系、锆系催化剂以及碳等添加剂可以显著改善配位氢化物的吸放氢动力学性能,加入催化剂可以使配位氢化物的可逆贮氢量达3.1%~4.2%(质量分数)。采用机械合金化法在NaAlH4中加入钛的化合物作为催化剂,在很大程度上改进了其热力学和动力学性能,可逆吸氢量可达4.0%以上,可逆放氢量也能达3.0%以上。并对试样进行了X射线衍射、扫描电镜以及X射线光电子能谱分析,证明了可逆反应的发生,探讨反应的机理。     

Effect of Promoters on the Permeation of electrolytic hydrogen through steel

Measurements of the permeation rate of electrolytic hydrogen through steel membranes have shown that compounds of P, As, Sb, S, Se, and Te enhance the entry of hydrogen into the steel only under conditions resulting in the formation of hydrides of hydrides of these elements. It may be presumed that the hydrides which are dissociatively chemisorbed on the cathode are able to assit in the transmission of hydrogen atoms across the electrolyte metal interface, while adsorbed hydroxylions, may be presumed to interfere with the action of hydrides and thus to inhibit permeation.