SAM法研究银透过金镀层的表面富集

基底元素透过镀层于表面富集可使镀层失去作用和意义,导致元、器件失效。对银上镀金样品的SAM法研究结果表明,常温下这种富集主要是基底元素通过缺陷和晶界扩散穿透镀层再行表面扩散而遍及表面的;镀件的表面吸附与表面富集的发生密切相关。文中给出了随时间的推移,银于表面富集情况的清晰的俄歇相。已发展出新的工艺,可以明显地延缓基底元素透过镀层到表面的富集。     

合金化热镀锌无间隙原子钢板表面白色点状压印缺陷的产生原因

使用扫描电子显微镜、能谱仪、光学显微镜等设备，对合金化热镀锌无间隙原子钢板表面白色点状压印缺陷进行分析，查明了该缺陷的产生原因。结果表明：该缺陷表面合金化不充分，平整印较多，锌层局部偏厚，部分溶锌后发现有氧化铁皮；钢板表面氧化铁皮局部偏厚，酸洗时氧化铁皮未能被完全溶解，并压在钢板表面，镀锌合金化后呈白色点状压印形貌。采用降低卷取温度的方法，可有效减小钢板表面氧化铁皮的厚度，后续钢板未再发现该类缺陷。     

线路钢轨断裂分析

湘桂线发生一起PD3钢轨横向断裂。经对钢轨断口的宏观分析，以及用光学显微镜进行金相分析、电子显微镜的断口微观分析和能谱微区成分测定。结果表明，钢轨轨底下表面中部有一沿钢轨纵向长17mm、宽12mm、深约3mm的外伤凹坑缺陷，凹坑底部有一层厚度不均的、最厚约1．0mm的铜铁合金熔融层，再往里是厚度达1．0mm的马氏体组织层。凹坑缺陷及其凹坑底部的铜铁合金熔融层的产生，是由于钢轨进行接触焊时在电极板与钢轨底面之间接触不良所产生的电打火造成。裂纹就起源于铜铁合金熔融层，然后裂纹快速向轨腰和轨头方向扩展造成钢轨横向断梨．     

固相萃取微色谱柱富集测定水小的Cu^2＋

采用固本萃取微色谱柱富集水中痕量铜离子继分光光度法测定的方法,本文对溶液PH值、洗脱剂的用量等诸多影响柱效的因素进行了研究,建立了一种简便测定水样中痕量铜离子的方法。结果表明,样品浓度低时,经过微色谱柱流速低,色谱柱富集效率高。当样品溶液中铜离子浓度为0-0.2ng/ml时,回收率大于90%,相对标准偏差为2.61%。     

热镀铝锌板黑线缺陷原因分析

为了查找薄规格热镀铝锌板黑线缺陷产生原因,采用ZEISS Merlin Compact场发射扫描电镜及其附带的OXFORD X-max N型能谱仪等分析技术对热镀铝锌钢板黑线缺陷表面、截面以及腐蚀去掉镀层后的钢铁基板表面进行了微观形貌观察和化学成分分析。结果表明：热镀铝锌钢板上表面黑线缺陷是由于钢铁基板划伤致使钝化膜较厚所致;热镀铝锌钢板下表面黑线缺陷是由于下表面镀层发生凹陷微变形致使钝化膜较厚所致。热镀铝锌钢板表面划伤以及镀层凹陷造成与周围其他位置对光的反射不同,形成了视觉上的黑线缺陷。     

固相萃取微色谱柱富集测定水中的Cu2+

采用固本萃取微色谱柱富集水中痕量铜离子继分光光度法测定的方法,本文对溶液pH值、洗脱剂的用量等诸多影响柱效的因素进行了研究,建立了一种简便测定水样中痕量铜离子的方法.结果表明,样品浓度低时,经过微色谱柱流速低,色谱柱富集效率高.当样品溶液中铜离子浓度为0～0.2 μg/ml时,回收率大于90%,相对标准偏差为2.61%.     

钢板表面平整度测试仪设计分析

本文介绍了钢板表面平整度测试仪的工作原理、测量传感器及系统组成，该测试仪能在线测量钢板表面的缺陷，并取得较好的效果。     

槽钢轧制裂缝与掉块缺陷原因分析

采用低倍检验、金相检验、扫描电镜观察以及能谱分析等方法对某Q235槽钢中间坯腿部裂缝和掉块等缺陷的成因进行了分析。结果表明：由于用于轧制该槽钢的钢坯内部存在严重的中心裂纹和角部裂纹等缺陷,以及钢坯化学成分中的残余元素铜含量较高并在钢坯表面富集,是造成该槽钢中间坯腿部裂缝与掉块缺陷产生的主要原因。     

310S不锈钢中厚板表面裂纹缺陷形成原因

针对310S不锈钢中厚板表面出现裂纹缺陷的问题,对其连铸坯进行了低倍组织检测及表面渗透检测,再对产生裂纹缺陷的热轧钢板进行了扫描电镜分析及金相检验。结果表明：热轧钢板明显分成再结晶和未再结晶区域,裂纹均位于再结晶区域;由于再结晶和未再结晶区域组织的变形抗力不同,在钢板轧制过程中,变形抗力弱的区域开始出现裂纹,并扩展到钢板表面,这是产生表面裂纹缺陷的主要原因。     

压痕应变法测试车桥用钢的表面残余应力

采用压痕应变法分别对某车桥用钢在单矫和复矫(二次矫直)工艺条件下表面残余应力的分布情况进行了研究。结果表明:车桥用钢在剪切下料后出现的板形缺陷与钢板表面的残余应力大小和分布有直接关系,当表面残余应力或者正反面残余应力的差值较大时,钢板容易出现瓢曲等板形缺陷。这也说明了应用压痕应变法测试钢板表面的残余应力可以在剪板前有效地预测钢板变形情况,应用该技术可以有效地指导钢板轧制和矫直工艺的调整。     

Fast integration and weight function blending in the extended finite element method

Two issues in the extended finite element method (XFEM) are addressed: efficient numerical integration of the weak form when the enrichment function is self‐equilibrating and blending of the enrichment. The integration is based on transforming the domain integrals in the weak form into equivalent contour integrals. It is shown that the contour form is computationally more efficient than the domain form, especially when the enrichment function is singular and/or discontinuous. A method for alleviating the errors in the blending elements is also studied. In this method, the enrichment function is pre‐multiplied by a smooth weight function with compact support to allow for a completely smooth transition between enriched and unenriched subdomains. A method for blending step function enrichment with singular enrichments is described. It is also shown that if the enrichment is not shifted properly, the weighted enrichment is equivalent to the standard enrichment. An edge dislocation and a crack problem are used to benchmark the technique; the influence of the variables that parameterize the weight function is analyzed. The resulting method shows both improved accuracy and optimum convergence rates and is easily implemented into existing XFEM codes. Copyright © 2008 John Wiley & Sons, Ltd.     

Defect studies of ZnSe nanowires

During the synthesis of ZnSe nanowires various point and extended defects can form, leading to observed stacking faults and twinning defects, and strong defect related emission in photoluminescence spectra. In this paper, we report on the development of a simple thermodynamic model for estimating the defect concentration in ZnSe nanowires grown under varying Se vapour pressure and for explaining the results of our experimental findings. Positron annihilation spectroscopy was used successfully for the first time for nanowires and the results support predictions from the defect model as well as agreeing well with our structural and optical characterization results. Under very high Se vapour pressure, Se nodules were observed to form on the sidewalls of the nanowire, indicating that beyond a limit, excess Se will begin to precipitate out of the liquid alloy droplet in the vapour-liquid-solid growth of nanowires.     

Centreline defects in strips produced through thin slab casting and rolling

Segregation in conventional slabs has been the topic of multiple researches; the centreline segregation in thin slabs has not been explicitly reported in published literature. However, a centreline band (defect) is invariably observed on macroetching high-manganese (>1?wt-%) strips from thin slab casting and rolling route of TATA Steel, Jamshedpur. A study was conducted to establish the exact nature of centreline defects and correlate with observation in the corresponding slab. Presence of second phases at the centreline due to heavy manganese enrichment was observed to be the source of defect band. In summary, this paper establishes a direct correlation between defects in hot-rolled strips and macrosegregation in thin slabs and highlights countermeasures taken to address the defect.     

Mg共掺杂Gd3(Al,Ga)5O12:Ce晶体快发光的作用机理

Gd₃(Al,Ga)₅O₁₂:Ce (GAGG:Ce)闪烁体综合性能优异, 应用前景广阔。为加快GAGG的发光衰减速度, 本研究通过提拉法生长了Mg共掺的Gd₃(Al,Ga)₅O₁₂:Ce单晶。测试结果显示, 随着Mg²⁺掺杂浓度增加, 晶体的闪烁衰减速度加快, 光输出降低。传统解释认为, Mg²⁺通过电荷补偿作用将部分Ce³⁺转换成Ce⁴⁺, 后者的发光速度更快。本研究尝试从缺陷的形成与抑制的角度来讨论Mg改善GAGG:Ce晶体闪烁性能的作用机理。由于Ce的离子半径比Gd大, Ce离子掺入将导致发光中心Ce_Gd附近的晶格发生畸变。畸变结果为近邻的八面体格位空间变大, 反位缺陷将更容易在这些变大的八面体格位形成。最终每个发光中心Ce_Gd被四个反位缺陷Gd_Al包裹, 后者捕获载流子, 延缓从基体到发光中心的能量传递, 导致发光速度变慢。由于Mg的离子半径介于Gd和Al之间, Mg_Al将更容易在上述畸变的八面体格位形成, 这会抑制反位缺陷Gd_Al在发光中心Ce_Gd附近形成(或富集), 最终降低(甚至消除)反位缺陷对发光中心的不良影响。XEL测试结果显示, 随着Mg掺杂量增大, 与反位缺陷相关的发射峰强度变弱, 这可以证明Mg对反位缺陷有抑制作用。     

α-β两相钛合金棒材常见偏析缺陷分析

对α-β两相钛合金棒材中发现的偏析缺陷进行了分析,并提出了减少或消除偏析缺陷的解决措施。结果表明:α-β两相钛合金棒材中的偏析缺陷一般以亮斑形式存在;偏析可分为间隙元素偏析和主合金化学成分偏析两大类,主合金化学成分偏析又可以分为合金元素贫化、α相稳定元素(主要是铝)富化和β相稳定元素富化3种;棒材中偏析缺陷的产生一般与合金熔炼有关,为了减少或消除偏析,应加强配料过程中间合金选择、电极制备(混布料)、合金熔炼等工艺的控制,并注重各工序间的质量检验。     

Iron(III) as a defect in diantimony tetroxide

Defect structures for Fe(III) in both alpha- and beta-diantimony tetroxide are explored using computer modelling techniques. A new favourable interstitial position for Fe(III) is identified, but the most energetically favourable defect reaction incorporating Fe(III) in diantimony tetroxide was found to be that in which the transition metal ion replaced an Sb(III) ion. The most favourable intrinsic defect in diantimony tetroxide is found to be an oxide ion Frenkel defect. This is considerably more favourable for the alpha form due to the asymmetric structure of this form. Incorporation of iron close to such a defect makes substitution on the Sb(III) site more favourable for the beta form.     

Investigations on the extrusion defect – Axial hole or funnel

Axial hole or funnel is a common extrusion defect observed during a direct extrusion process. Though a common defect, the parameters that influence the nature and formation of this defect have not been studied and reported. Further, the die design requirement to avoid the defect has also been not yet established. In this regard, finite element analysis has been carried out to investigate the effect of important extrusion parameters such as extrusion ratio (R), extrusion die angle (θ), deformation zone height (h), friction (μ) and constitutive material behaviour on the defect formation and its characteristic. The conditions under which the defect can be avoided have been established. Physical modeling experiments using plasticine were carried out to validate the numerical modeling results.     

Defect properties in a VTaCrW equiatomic high entropy alloy(HEA)with the body centered cubic(bcc) structure

We report first-principles results of the point defect properties in a V-Ta-Cr-W high-entropy alloy(HEA)with the body-centered cubic(bcc) structure. Different from the widely-investigated face-centered cubic(fcc) HEAs, the local lattice distortion is more pronounced in bcc ones, which has a strong influence on the defect properties and defect evolution under irradiation. Due to the large size of Ta, the exchange between vacancies and Ta exhibits lower energy barriers. On the other hand, interstitial dumbbells containing V and Cr possess lower formation energies. These defect energetics predicts an enrichment of V and Cr and a depletion of Ta and W in the vicinity of defect sinks. Besides, we find that interstitial dumbbells favor the [110] orientation in the HEA, instead of [111] direction in most nonmagnetic bcc metals,which helps to slow down interstitial diffusion significantly. Consequently, the distribution of migration energies for vacancies and interstitials exhibit much larger overlap regions in the bcc HEA compared to fcc HEAs, leading to the good irradiation resistance by enhancing defect recombination. Our results suggest that HEAs with the bcc structure may bear excellent irradiation tolerance due to the particular defect properties.     

Singularity enrichment for complete sliding contact using the partition of unity finite element method

In this paper, the numerical modelling of complete sliding contact and its associated singularity is carried out using the partition of unity finite element method. Sliding interfaces in engineering components lead to crack nucleation and growth in the vicinity of the contact zone. To accurately capture the singular stress field at the contact corner, we use the partition of unity framework to enrich the standard displacement‐based finite element approximation by additional (enriched) functions. These enriched functions are derived from the analytical expression of the asymptotic displacement field in the vicinity of the contact corner. To characterize the intensity of the singularity, a domain integral formulation is adopted to compute the generalized stress intensity factor (GSIF). Numerical results on benchmark problems are presented to demonstrate the improved accuracy and benefits of this technique. We conduct an investigation on issues pertaining to the extent of enrichment, accurate numerical integration of weak‐form integrals and the rate of convergence in energy. The use of partition of unity enrichment leads to accurate estimations of the GSIFs on relatively coarse meshes, which is particularly beneficial for modelling non‐linear sliding contacts. Copyright © 2008 John Wiley & Sons, Ltd.     

RTM成型复合材料中微观缺陷表征及分析

通过对RTM成型复合材料制件及其预成型体进行解剖,并采用光学显微镜及扫描电镜对制件缺陷及预成型体表征,结果显示预成型体中定型剂富集的铺层与缺陷位置一致;并分析了缺陷表观形貌,阐述了缺陷形成原因。