分类: 材料科学 >> 材料科学(综合) 提交时间: 2022-05-31
A novel hybrid laser additive manufacturing process based on laser shock modulation of molten pool was proposed in this work. The flow behavior residual stress, and microstructure of the molten pool were comprehensively characterized by a combination of experiments and simulations. The relationship between the convection behavior, evolution of microstructure, and enhancement of residual stress induced by laser shock modulation was established. Laser shock modulation assisted additive manufacturing process exhibits high efficiency in residual stress control. The hidden mechanism in microstructure evolution and residual stress enhancement was expected to be related to intensified molten pool convection, uniform solute distribution and improved cooling rate induced by shock wave. The hybrid additive manufacturing process strategy based on laser shock modulation provides a new approach for heat and mass modulation in hybrid manufacturing.
分类: 材料科学 >> 电子、光学、磁材料 分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2022-05-08
本文研究近紫外飞秒激光脉冲在聚甲基戊烯内部刻写的应用技术。我们发现该热塑材料具有偏振敏感性的特征。首先刻写实验使用数字孔径为0.05的透镜聚焦, 通过对超连续光谱的分析,测得稳定成丝刻写的激光脉冲功率在2.2MW - 9.2MW区间内,并由此推断该种材料的非线性折射率为n2387=2×10-16cm2W-1,推算三阶susceptibility χ(3)为 1.1×10-14esu。稳定成丝加工长度在300μm-1500μm。然后,实验使用数字孔径为0.4的组合物镜聚焦刻写厚度为~700μm,栅距为5μm的布拉格光栅。通过对光栅产品的衍射效率测试,推断最大折射率的变化为~0.01,这比文献中的记录数据,提高一个数量级。实验结果证明了激光脉冲峰值强度对于诱导非线性吸收的重要性,而双光子吸收为温和可控改性的物理机制。本工作为科研人员和光学器件设计和制作提供了最新的参考。
分类: 材料科学 >> 电子、光学、磁材料 提交时间: 2022-03-07
In this paper, we reported a method to modify the crystallization of CZTSSe films by changing the microstructures of the precursor films. Precursor films with different microstructures were prepared and their crystallization processes were analyzed. We find even tiny differences in microstructures of the precursor films can result in significant alteration of the crystallization processes and the properties of CZTSSe films. Moreover, we found the S-to-Se substitution can be delayed to higher temperature depending on the microstructure of the precursor. This process plays critical roles in enhanceing the crystallization of CZTSSe films and can be used to eliminate the multi-layer crystallization in CZTSSe films. The detailed analysis on the crystallization processes revealed that different mechanism may dominate the crystallization of the films, which can determine the properties of CZTSSe films and solar cells. Moreover, a hybrid structure for precursor film was proposed which has different microstructures in different part of the film. In such a precursor film, different crystallization mechanism can work synergically during the preparation of the film. As the results, the comprehensive properties of the films were improved and solar cells with efficiencies up to 12.6% was prepared.
分类: 材料科学 >> 复合材料 提交时间: 2021-08-13
摘要: In recent decades, carbon fiber reinforced thermoplastic from the wet-laid process (WL-CTP) appeals to attention for its simplicity and compatibility with recycled carbon fibers. However, there is still no constitutive model for the consolidation of WL-CTP. This study proposes a constitutive model based on the constitutive equation describing the compress behavior of the dry/impregnated CF network. Three deductions raised from the consolidation model were validated by the experiments investigating the effect of molding time, pressure, and temperature on the void volume fraction of the WL-CTP. Flexural testing further investigated the effect of molding time, pressure, and temperature on the flexural modulus and strength of the WL-CTP. It reveals that the molding pressure can be the only factor affecting the consolidation and flexural properties of the WL-CTP, which indicates that the WL-CTP with low void content and qualified mechanical properties can be produced under a relatively low temperature and high productivity.
分类: 材料科学 >> 纳米科学和纳米技术 提交时间: 2021-03-26
摘要: 太阳能蒸馏器由于其简单的结构和环保的能力,近年来引起了越来越多的关注。在本研究中,利用一种成熟的机器学习算法——随机森林,得到环境因子对蒸发效率的加权值。为了检验随机森林与数学数据分析之间的先进性,我们采用了两种传统的数据科学方法——配对图法和皮尔逊相关分析法进行比较。分析中使用的实验数据来自2014年以来的约100篇文章。结果表明,热设计是实现太阳能高效蒸发的最重要因素。这将促进太阳能蒸馏器蒸发效率的研究。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2020-08-12
摘要: Graphene has well demonstrated its unique properties and advantageous performances in lots of fields during the last 16 years. However, its industrial applications are still impeded by inefficient mass fabrication of high-quality graphene because of the great challenge in deep yet non-destructive graphite exfoliation. Herein, we demonstrated a delocalized electrochemical exfoliation (DEE) technique to efficiently fabricate high-quality graphene. Importantly, chemically transmitting the electric potentials was firstly proposed to spatially extend the exfoliation capability of electric potentials and electrochemically exfoliate every graphite particle dispersed in the electrolyte. The resulting graphene possesses ultralow defect density (ID/IG~0.07) and extremely high carbon-to-oxygen ratio (~28). Remarkably, high yields (~98.4%, 1-10 layers) and record high production rates (~72.7 g h?1) are realized in up-scaled batch of DEE. Further mechanism investigation revealed that the exfoliation capability of the electric potentials was transmitted to the whole electrolyte system by a dynamically favorable pathway. This pathway includes electrochemical oxidation, intercalation and interlayer bubble generation reactions, which makes deep and non-destructive exfoliation possible for every dispersed graphite particle in a scalable and reproducible manner. This way of using electric potentials differs from existing electrochemical methods and guarantees high throughput as well as high quality. The strategy of delocalized electrochemical exfoliation and the underlying concept of chemically transmitting the electric potentials would accelerate the commercialization of graphene and inspire more efficient fabrication of two-dimensional materials.
分类: 材料科学 >> 材料科学(综合) 分类: 材料科学 >> 金属与冶金 提交时间: 2020-01-07
摘要: Nano-crystalline metals (NCs) exhibit radiation-tolerance due to the sink of grain boundaries (GBs) for radiation-induced defects such as self-interstitial atoms (SIAs) and vacancies (Vs). However, the relevant mechanisms for the radiation damage accumulation and GB structural relaxation under high radiation field in NCs are still not well understood due to the lack of self-consistent across-scale techniques for simulating radiation-induced microstructures evolution. In this article, by combining coarse-grained and atomistic simulations, we proposed a coupling method to investigate the evolution of the microstructure and SIA/V-GB interaction under cumulative irradiation in NC iron. The SIA overloaded effect was revealed in iron GBs at a high radiation dose rate and/or low temperature. Two types of GB structural response were observed to cumulative irradiation. With the SIA accumulated at the GB, the new GB phase formed and then a critical concentration of the SIA at the GB transited to the small quantity of the V during the GB structural recovery, accompanied by the local GB motion. Consequently, the GB’s role for Vs nearby alternated between the trapping and annihilation center with radiation dose. Alternatively, GB developed to a disordered structure after trapping abundant SIAs. The GB response pattern to cumulative irradiation that is related to the SIA formation energy at the GB or the GB thermal stability is well manifested in the cumulative distribution function of the defects formation energy and its energy level density. The present work reveals the dynamic healing picture for radiation damage near the GB under cumulative irradiation.
分类: 材料科学 >> 电子、光学、磁材料 提交时间: 2019-04-30
摘要:我们成功合成了CsKNaLi(Li3SiO4)4:Eu2+ (CKNLLSO:Eu2+)作为UCr4C4型结构氧基家族的新成员。该荧光粉的基质化合物的晶体结构和能带结构分别通过Rieveld精修方法和密度泛函理论分析和计算。由于高度压缩和刚性的阴离子骨架,取代Cs格位的Eu2+在InGaN基紫外LED的激发下,发出了明亮的绿色荧光,半峰宽为55 nm.当温度升高到190℃时,CKNLLSO:Eu2+的稳定性仍然较好。采用浓度优化的CKNLLSO:4%Eu2+制成的LED器件发出的绿光的色坐标为(0.2320, 0.6016),相关色温为7314K。分析结果表明,这种荧光粉是一种很有前景的白光LED绿色荧光粉。
分类: 材料科学 >> 材料力学 提交时间: 2019-02-01
摘要:Magnetorheological (MR) materials are a type of magnetoactive smart materials, whose physical or mechanical properties can be altered by applying a magnetic field. In usual, MR materials can be prepared by mixing magnetic particles into non-magnetic matrices. In this work, the electromagnet-induced (or non-uniform magnetic field-induced) normal stress of MR materials is studied. It shows that the stress does not vary monotonically along with the enhancement of the applied magnetic field. There exists a field-dependent reversal effect of the variation of the stress. The reversal effect is thought resulting from that the ratio of interparticle repellent of parallel magnetic particles to the particle-electromagnet attraction gets enlarged along with the enhancement of the field.
分类: 材料科学 >> 金属与冶金 提交时间: 2018-09-14
摘要: 理解合金元素如何调制金属材料的弹性模量在固体物理理论及金属材料的机械性能的工程设计领域都很重要。本文采用第一性原理方法计在合金原子浓度在 0.4 到 1.85 at% 范围内 12 种铁基固溶体的弹性模量并研究合金元素对 bcc 铁基体弹性模量的机制。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2018-09-03
摘要: Silver orthophosphate (Ag3PO4) has aroused widespread interest since the discovery of visible-light-driven photocatalysis activity. However, its indirect bandgap nature at ambient becomes an obstacle to improve the photocatalysis efficiency and use in other application fields. In this study, the indirect-to-direct bandgap crossover was found during the pressure-induced phase transition from cubic to trigonal phase in Ag3PO4. The observed bandgap narrowing could be partially retained after pressure was released to ambient conditions, accelerating to efficiently utilize the solar spectrum. Moreover, Ag3PO4 was ductile like metals. Unexpectedly, this ion-conducting and ductile semiconductor photocatalyst further exhibited the negative linear compressibility (NLC) at pressure range of 7.5-25 GPa. This work, combining experimental and theoretical tools, provides an insight into the modulation mechanism of the electronic structure for silver-based semiconductors, and may broaden the applications of Ag3PO4.
分类: 材料科学 >> 材料化学 提交时间: 2018-01-27
摘要:生物矿化领域的研究者普遍接受珍珠层板片是由非晶质碳酸钙(ACC)纳米颗粒相变而成。然而,这些纳米颗粒在三维空间是如何排列的及如何相变的仍未清楚。本文首次报道了一种新类型不成熟板片,即“枝晶状板片”。这种板片发育在翡翠贻贝珍珠层中。通过与颗粒状板片形貌进行对比,我们发现ACC纳米颗粒通常自组装成垂直的团簇且相变成垂直定向的文石小晶体。这种小晶体与无机成因的文石晶体的平衡形状相同。最重要的是,我们首次发现文石板片与层间有机膜(ILM)呈高的接触角(99-126度)。这表明ILM对ACC纳米颗粒是非润湿的。这种非润湿性可能对珍珠层的形貌成因有重要影响。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-11-21 合作期刊: 《材料研究学报》
降低与金属之间的接触电阻是碳纳米管在微纳电子领域获得应用的前提,掺杂金纳米粒子可有效降低碳纳米管的接触电阻。本文采用高温焙烧在碳纳米管表面构造缺陷和亲水基团,然后将碳纳米管在氯金酸水溶液中超声浸泡以吸附氯金酸,再在氢气气氛下加热还原氯金酸为金。扫描电子显微(SEM)图片表明碳纳米管被成功地掺杂了金纳米粒子,X射线能量散射谱(EDS)和X射线光电子谱(XPS)表明金是唯一掺杂在碳纳米管上的粒子。掺杂后碳纳米管的拉曼光谱中G带波数降低说明对碳纳米管掺杂金为N型掺杂。N型掺杂剂将电子转移给邻近的碳原子,使碳纳米管中的电子数量增加,进而增强了碳纳米管的导电性。利用介电电泳法将碳纳米管组装到一对金电极之间,并使用精密电感电容电阻(LCR)测试仪实时测量。结果表明碳纳米管与金电极之间的接触电阻较掺杂前得到了有效改善,电阻值最大可降低近50%。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-11-21 合作期刊: 《材料研究学报》
以硅藻土为载体、以石蜡为相变材料,用溶剂蒸发法制备出石蜡/硅藻土定型相变材料(PA/D-PCMs),使用SEM、FT-IR、TGA、DSC等手段对其微观结构和热性能进行了表征。结果表明:硅藻土对石蜡的毛细管力及两者之间形成的氢键能阻碍液态石蜡的渗出,使PA/D-PCMs具有很高的热稳定性,硅藻土的二级孔洞限制了部分石蜡的结晶。硅藻土内部有许多互相连通的导热通道,增强了石蜡的导热效果并提高了蓄放热速率。随着石蜡含量的增大PA/D-PCMs的X、Y和Z轴传热通道上声子的散射作用更剧烈,使其导热系数降低,但是具有更高的结晶度和相变潜热。为了保证PA/D-PCMs的结构稳定和良好的热性能,石蜡的最佳质量分数为45%。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-11-21 合作期刊: 《材料研究学报》
以氧化铝、氢氧化铝、勃姆石为水不溶性金属源,用水热法合成了金属有机骨架MIL-53(Al)。使用SEM、XRD、氮气吸附和TGA表征了产物的形貌和结构,并与用传统水溶性硝酸铝合成的MIL-53(Al)对比。结果表明:使用三种水不溶性金属源都能合成典型的金属有机骨架材料MIL-53(Al)。用水热法制备的MIL-53(Al)产物的BET比表面积都在700~1000 m2/g。结果还表明,使用三种水不溶性金属源合成的MIL-53(Al)骨架的柔性(flexibility)与用常规铝硝酸盐合成的MIL-53(Al)不同。使用氧化铝合成的MIL-53(Al)常温下的孔道主要呈现大孔(lp)结构且骨架刚性较强。与使用其他铝源合成的MIL-53(Al)相比,用氧化铝合成的MIL-53(Al)对洛克沙胂有较好的吸附去除效果,吸附过程符合二级动力学模型。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-11-21 合作期刊: 《材料研究学报》
在聚氧化丙烯多元醇(PPG)和二苯基甲烷二异氰酸酯(MDI)组成的交联聚氨酯(CPU)体系的基础上添加聚醚改性MQ树脂(E-MQ),制备出E-MQ树脂增强的浇注型聚氨酯弹性体。结果表明:E-MQ树脂与CPU有良好的相容性,制备出的E-MQ增强弹性体具有良好的力学性能。当E-MQ树脂用量为8%(E-MQ树脂占聚氨酯弹性体总质量分数)时增强聚氨酯弹性体的拉伸强度可达20.8 MPa,比CPU基础样提高22.4%,撕裂强度为82 kNm-1,邵尔A硬度为82度。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-11-21 合作期刊: 《材料研究学报》
对11.5CrNbTi和15Cr0.5MoNbTi超纯铁素体不锈钢进行650℃应力控制循环蠕变实验,研究了最大外加应力处引入的保持时间对铁素体不锈钢的循环蠕变变形和断裂行为的影响。结果表明:保持时间的延长使这两种不锈钢的最小循环蠕变速率增大,循环蠕变寿命和循环断裂周次减少。在相同的条件下,15Cr0.5MoNbTi不锈钢的循环蠕变抗力优于11.5CrNbTi不锈钢。这两种不锈钢的循环蠕变断裂模式均为穿晶断裂,随着保持时间的延长断口表面的蠕变孔洞增多,蠕变损伤作用增强。这两种不锈钢循环蠕变后的微观组织均为亚晶,位错的滑移和交滑移是循环蠕变的主要变形机制。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-11-21 合作期刊: 《金属学报》
摘要:研究了溅射Al对Si3N4的润湿作用和Al及Al-Ni合金薄膜钎料对Si3N4陶瓷的钎焊。结果表明,高能量溅射Al粒子的直接撞击可以实现Al对Si3N4的“润湿”,使Al和Al-Ni合金薄膜熔化后即可对Si3N4陶瓷进行钎焊。所获得接头的钎缝致密饱满,与陶瓷形成无反应过渡层的良好冶金结合,纯Al钎焊接头的剪切强度为106 MPa,Al-1.0 at.% Ni亚共晶钎焊接头的强度提高到148 MPa,Al-3.0 at.% Ni接头的强度因钎缝形成共晶组织而略有降低,为132 MPa。相对于以上各接头的剪切断裂均产生于钎缝之中,当溅射Al粒子因Ni层阻挡不能直接撞击Si3N4表面时,Al-1.0 at.% Ni薄膜钎料熔化后不能润湿Si3N4,所得接头的剪切断裂发生在钎缝与陶瓷的界面,强度也降低为81 MPa。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-11-21 合作期刊: 《金属学报》
摘要:应用锌盐与氨水以及单氰胺水溶液间配体交换反应,制备了氰胺锌(ZnNCN)颗粒。并通过在前驱体盐溶液中共混银盐,利用相同的配体交换反应过程,制备了氰胺银(Ag2NCN)/ZnNCN复合颗粒。利用XRD、SEM、红外光谱(FT-IR)和紫外-可见(UV-Vis)吸收光谱对光催化剂的结构进行表征。结果表明,单一ZnNCN为花瓣状颗粒,宽禁带半导体材料(Eg=4.66 eV)。Ag2NCN/ZnNCN复合颗粒形貌与单一ZnNCN和Ag2NCN相比较有很大变化,两种金属氰胺化物以弱的物理作用力结合形成异质结构,复合颗粒的光谱响应范围扩展至可见光区,禁带宽度Eg=2.05 eV。以罗丹明B为光催化降解对象,研究了ZnNCN、Ag2NCN/ZnNCN复合颗粒在氙灯激发下的光催化活性。与单一ZnNCN以及Ag2NCN、ZnNCN机械混合物相比,Ag2NCN/ZnNCN复合颗粒表现出增强的光催化性能,表现为一级反应动力学特征。